Bio

Bio


Professor Dai’s research spans chemistry, physics, and materials and biomedical sciences, leading to materials with properties useful in electronics, energy storage and biomedicine. Recent developments include near-infrared-II fluorescence imaging, ultra-sensitive diagnostic assays, a fast-charging aluminum battery and inexpensive electrocatalysts that split water into oxygen and hydrogen fuels.

Born in 1966 in Shaoyang, China, Hongjie Dai began his formal studies in physics at Tsinghua U. in Beijing (B.S. 1989) and applied sciences at Columbia U. (M.S. 1991). His doctoral work under Dr. Charles Lieber at Harvard U. (Ph.D. 1994) focused on charge-density waves and superconductivity. During postdoctoral research at Rice U. with Dr. Richard Smalley, he developed carbon nanotube probes for atomic force microscopy. He joined the Stanford faculty in 1997, and in 2007 was named Jackson–Wood Professor of Chemistry. Among many awards, he has been recognized with the ACS Pure Chemistry Award, APS McGroddy Prize for New Materials, Julius Springer Prize for Applied Physics and Materials Research Society Mid-Career Award. He has been elected to the American Academy of Arts and Sciences, AAAS and National Academy of Sciences.

The Dai Laboratory has advanced the synthesis and basic understanding of carbon nanomaterials and applications in nanoelectronics, nanomedicine, energy storage and electrocatalysis.

Nanomaterials
The Dai Lab pioneered some of the now-widespread uses of chemical vapor deposition for carbon nanotube (CNT) growth, including vertically aligned nanotubes and patterned growth of single-walled CNTs on wafer substrates, facilitating fundamental studies of their intrinsic properties. The group developed the synthesis of graphene nanoribbons, and of nanocrystals and nanoparticles on CNTs and graphene with controlled degrees of oxidation, producing a class of strongly coupled hybrid materials with advanced properties for electrochemistry, electrocatalysis and photocatalysis. The lab’s synthesis of a novel plasmonic gold film has enhanced near-infrared fluorescence up to 100-fold, enabling ultra-sensitive assays of disease biomarkers.

Nanoscale Physics and Electronics
High quality nanotubes from his group’s synthesis are widely used to investigate the electrical, mechanical, optical, electro-mechanical and thermal properties of quasi-one-dimensional systems. Lab members have studied ballistic electron transport in nanotubes and demonstrated nanotube-based nanosensors, Pd ohmic contacts and ballistic field effect transistors with integrated high-kappa dielectrics.

Nanomedicine and NIR-II Imaging
Advancing biological research with CNTs and nano-graphene, group members have developed π–π stacking non-covalent functionalization chemistry, molecular cellular delivery (drugs, proteins and siRNA), in vivo anti-cancer drug delivery and in vivo photothermal ablation of cancer. Using nanotubes as novel contrast agents, lab collaborations have developed in vitro and in vivo Raman, photoacoustic and fluorescence imaging. Lab members have exploited the physics of reduced light scattering in the near-infrared-II (1000-1700nm) window and pioneered NIR-II fluorescence imaging to increase tissue penetration depth in vivo. Video-rate NIR-II imaging can measure blood flow in single vessels in real time. The lab has developed novel NIR-II fluorescence agents, including CNTs, quantum dots, conjugated polymers and small organic dyes with promise for clinical translation.

Electrocatalysis and Batteries
The Dai group’s nanocarbon–inorganic particle hybrid materials have opened new directions in energy research. Advances include electrocatalysts for oxygen reduction and water splitting catalysts including NiFe layered-double-hydroxide for oxygen evolution. Recently, the group also demonstrated an aluminum ion battery with graphite cathodes and ionic liquid electrolytes, a substantial breakthrough in battery science.

Honors & Awards


  • Member, National Academy of Sciences (2016)
  • Mid-Career Researcher Award, Materials Research Society (2016)
  • Honorary Chair Professor, National Taiwan University of Science and Technology (2015)
  • Fellow, American Association for the Advancement of Sciences (2010)
  • Fellow, American Academy of Arts and Sciences (2009)
  • The Ramabrahmam and Balamani Guthikonda Award, Columbia University (2009)
  • James McGroddy Prize for New Materials, American Physical Society (2006)
  • Julius Springer Prize of Applied Physics, Editors of Applied Physics A and Applied Physics B, Springer (2004)
  • Camille Dreyfus Teacher-Scholar Award, Camille & Henry Dreyfus Foundation (2002)
  • Pure Chemistry Award, American Chemical Society (2002)
  • Alfred P. Sloan Research Fellow, Alfred P. Sloan Foundation (2001)
  • Packard Fellowship for Science and Engineering, David & Lucile Packard Foundation (1999)
  • Terman Fellowship, Stanford University (1998)
  • Young Microscopist of the Year Award, Molecular Imaging Co. (1998)
  • Camille and Henry Dreyfus New Faculty Award, Rice University (1997)

Boards, Advisory Committees, Professional Organizations


  • Scientific Advisor and Co-founder, Nirmidas Biotech, Inc.
  • Editor-in-Chief, Nano Research, Springer
  • Editorial Board Member, Nano Letters, American Chemical Society
  • Editorial Board Member, Nano Research, Springer and Tsinghua University Press
  • Editorial Board Member, Advanced Functional Materials, Wiley-VCH Verlag GmbH.
  • Editorial Board Member, International Journal of Nanoscience, World Scientific, Singapore
  • Editorial Board Member, Chemical Physics Letters
  • Editorial Board Member, Nanotechnology, Institute of Physics, England
  • Editorial Board Member, Small, Wiley-VCH Verlag
  • Editorial Board Member, Applied Physics A, Springer

Professional Education


  • Postdoc, Harvard University, Charge density waves/Superconductor (1997)
  • Postdoc, Rice University, Carbon nanotubes for AFM (1995)
  • PhD, Harvard University, Applied Physics/Physical Chemistry (1994)
  • MS, Columbia University, Applied Sciences (1991)
  • BS, TsingHua University, Physics (1989)

Teaching

2016-17 Courses


Stanford Advisees


Publications

All Publications


  • Visible to Near-Infrared Fluorescence Enhanced Cellular Imaging on Plasmonic Gold Chips SMALL Koh, B., Li, X., Zhang, B., Yuan, B., Lin, Y., Antaris, A. L., Wan, H., Gong, M., Yang, J., Zhang, X., Liang, Y., Dai, H. 2016; 12 (4): 457-465

    Abstract

    Rapid and sensitive detections of a variety of surface and intracellular proteins, nucleic acids, and other cellular biomarkers are important to elucidating biological signaling pathways and to devising disease diagnostics and therapeutics. Here, sensitive imaging and detection of cellular proteins on fluorescence-enhancing, nanostructured plasmonic gold (pGold) chips is presented. Imaging of fluorescently labeled cellular biomarkers on pGold is enhanced by 2-30-fold in the visible to near infrared (NIR) range of ≈500-900 nm. The high fluorescence enhancement of >700 nm significantly improves the dynamic range and signal/background ratios of NIR imaging, allowing high-performance multicolor imaging in the visible-NIR range using high quantum yield (QY) visible dyes and lower QY NIR fluorophores. Further, multiple cellular proteins of single cells of various cell types can be detected through microarraying of cells, useful for potentially hundreds and thousands different types of cells assayed on a single chip down to small cell numbers. This work suggests a simple, high throughput, high sensitivity, and multiplexed single-cell analysis method on fluorescence enhancing plasmonic substrates in the entire visible to NIR window.

    View details for DOI 10.1002/smll.201502182

    View details for Web of Science ID 000368840500006

    View details for PubMedID 26663862

  • A mini review on nickel-based electrocatalysts for alkaline hydrogen evolution reaction NANO RESEARCH Gong, M., Wang, D., Chen, C., Hwang, B., Dai, H. 2016; 9 (1): 28-46
  • Energy Migration Engineering of Bright Rare-Earth Upconversion Nanoparticles for Excitation by Light-Emitting Diodes ADVANCED MATERIALS Zhong, Y., Rostami, I., Wang, Z., Dai, H., Hu, Z. 2015; 27 (41): 6418-?
  • Blending Cr2O3 into a NiO-Ni Electrocatalyst for Sustained Water Splitting ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Gong, M., Zhou, W., Kenney, M. J., Kapusta, R., Cowley, S., Wu, Y., Lu, B., Lin, M., Wang, D., Yang, J., Hwang, B., Dai, H. 2015; 54 (41): 11989-11993

    Abstract

    The rising H2 economy demands active and durable electrocatalysts based on low-cost, earth-abundant materials for water electrolysis/photolysis. Here we report nanoscale Ni metal cores over-coated by a Cr2 O3 -blended NiO layer synthesized on metallic foam substrates. The Ni@NiO/Cr2 O3 triphase material exhibits superior activity and stability similar to Pt for the hydrogen-evolution reaction in basic solutions. The chemically stable Cr2 O3 is crucial for preventing oxidation of the Ni core, maintaining abundant NiO/Ni interfaces as catalytically active sites in the heterostructure and thus imparting high stability to the hydrogen-evolution catalyst. The highly active and stable electrocatalyst enables an alkaline electrolyzer operating at 20 mA cm(-2) at a voltage lower than 1.5 V, lasting longer than 3 weeks without decay. The non-precious metal catalysts afford a high efficiency of about 15 % for light-driven water splitting using GaAs solar cells.

    View details for DOI 10.1002/anie.201504815

    View details for Web of Science ID 000363396000015

    View details for PubMedID 26307213

  • Biological imaging without autofluorescence in the second near-infrared region NANO RESEARCH Diao, S., Hong, G., Antaris, A. L., Blackburn, J. L., Cheng, K., Cheng, Z., Dai, H. 2015; 8 (9): 3027-3034
  • Cytokine detection and simultaneous assessment of rheumatoid factor interference in human serum and synovial fluid using high-sensitivity protein arrays on plasmonic gold chips BMC BIOTECHNOLOGY Valentina, M., Jan, F., Peder, N. L., Bo, Z., Dai Hongjie, H. J., Pernille, K. 2015; 15

    Abstract

    Fluorescence-enhancing microarray on plasmonic gold film is an attractive alternative to traditional enzyme-linked immunosorbent assay (ELISA) for cytokine detection because of the increased sensitivity. The assay chemistry is similar to an ELISA sandwich assay, but owing to the gold substrate, cytokine measurements are 10 to 100 times more sensitive and can be multiplexed. Plasmonic protein microarrays are, as other immunoassays, affected by the presence of heterophilic antibodies and rheumatoid factor may lead to analytical errors with serious implications for patient care. Here, we present a plasmonic gold substrate protein microarray for high-sensitivity detection of cytokines with simultaneous assessment of rheumatoid factor interference on a single chip.Paired serum and synovial fluid samples from patients with rheumatoid arthritis (n = 18), osteoarthritis (n = 9) or healthy controls (n = 10) were arrayed on near-infrared fluorescence enhancing plasmonic gold chips spotted with cytokine-specific capture antibody and isotype control antibody. Possible rheumatoid factor interference was visualised by a non-specific signal from the isotype control antibody, and pre-treatment of samples with heat-aggregated animal IgG eliminated this background contamination. The platform was optimised using the cytokine IL-20. The protein microarray platform allowed for the detection of human IL-20 at levels <1 pg/ml with reliable IL-20 quantification over a 5-log dynamic range. Samples for which rheumatoid factor caused artefacts were identified and a method for eliminating rheumatoid factor interference was developed and validated. IL-20 protein levels were significantly higher in synovial fluid samples from patients with rheumatoid arthritis compared to osteoarthritis (p < 0.001), while serum levels of IL-20 did not differ between patients with rheumatoid arthritis, osteoarthritis or healthy controls.Using novel plasmonic gold chips, we developed a highly sensitive and accurate assay platform to detect lowly expressed cytokines in biological fluids, allowing for the elimination of rheumatoid factor interference in as little as 5 μl sample volume. The detection limit was below 1 pg/ml for IL-20 and linearity was achieved over a 5-log dynamic range. This technology is highly advantageous for cytokines where sensitivity or sample volume is critical or where assessment of rheumatoid factor interference needs addressed and eliminated.

    View details for DOI 10.1186/s12896-015-0186-0

    View details for Web of Science ID 000359337200002

    View details for PubMedID 26268325

  • Aligned-Braided Nanofibrillar Scaffold with Endothelial Cells Enhances Arteriogenesis. ACS nano Nakayama, K. H., Hong, G., Lee, J. C., Patel, J., Edwards, B., Zaitseva, T. S., Paukshto, M. V., Dai, H., Cooke, J. P., Woo, Y. J., Huang, N. F. 2015; 9 (7): 6900-6908

    Abstract

    The objective of this study was to enhance the angiogenic capacity of endothelial cells (ECs) using nanoscale signaling cues from aligned nanofibrillar scaffolds in the setting of tissue ischemia. Thread-like nanofibrillar scaffolds with porous structure were fabricated from aligned-braided membranes generated under shear from liquid crystal collagen solution. Human ECs showed greater outgrowth from aligned scaffolds than from nonpatterned scaffolds. Integrin α1 was in part responsible for the enhanced cellular outgrowth on aligned nanofibrillar scaffolds, as the effect was abrogated by integrin α1 inhibition. To test the efficacy of EC-seeded aligned nanofibrillar scaffolds in improving neovascularization in vivo, the ischemic limbs of mice were treated with EC-seeded aligned nanofibrillar scaffold; EC-seeded nonpatterned scaffold; ECs in saline; aligned nanofibrillar scaffold alone; or no treatment. After 14 days, laser Doppler blood spectroscopy demonstrated significant improvement in blood perfusion recovery when treated with EC-seeded aligned nanofibrillar scaffolds, in comparison to ECs in saline or no treatment. In ischemic hindlimbs treated with scaffolds seeded with human ECs derived from induced pluripotent stem cells (iPSC-ECs), single-walled carbon nanotube (SWNT) fluorophores were systemically delivered to quantify microvascular density after 28 days. Near infrared-II (NIR-II, 1000-1700 nm) imaging of SWNT fluorophores demonstrated that iPSC-EC-seeded aligned scaffolds group showed significantly higher microvascular density than the saline or cells groups. These data suggest that treatment with EC-seeded aligned nanofibrillar scaffolds improved blood perfusion and arteriogenesis, when compared to treatment with cells alone or scaffold alone, and have important implications in the design of therapeutic cell delivery strategies.

    View details for DOI 10.1021/acsnano.5b00545

    View details for PubMedID 26061869

  • Diketopyrrolopyrrole (DPP)-Based Donor-Acceptor Polymers for Selective Dispersion of Large-Diameter Semiconducting Carbon Nanotubes SMALL Lei, T., Lai, Y., Hong, G., Wang, H., Hayoz, P., Weitz, R. T., Chen, C., Dai, H., Bao, Z. 2015; 11 (24): 2946-2954

    Abstract

    Low-bandgap diketopyrrolopyrrole (DPP)-based polymers are used for the selective dispersion of semiconducting single-walled carbon nanotubes (s-SWCNTs). Through rational molecular design to tune the polymer-SWCNT interactions, highly selective dispersions of s-SWCNTs with diameters mainly around 1.5 nm are achieved. The influences of the polymer alkyl side-chain substitution (i.e., branched vs linear side chains) on the dispersing yield and selectivity of s-SWCNTs are investigated. Introducing linear alkyl side chains allows increased polymer-SWCNT interactions through close π-π stacking and improved C-H-π interactions. This work demonstrates that polymer side-chain engineering is an effective method to modulate the polymer-SWCNT interactions and thereby affecting both critical parameters in dispersing yield and selectivity. Using these sorted s-SWCNTs, high-performance SWCNT network thin-film transistors are fabricated. The solution-deposited s-SWCNT transistors yield simultaneously high mobilities of 41.2 cm(2) V(-1) s(-1) and high on/off ratios of greater than 10(4) . In summary, low-bandgap DPP donor-acceptor polymers are a promising class of polymers for selective dispersion of large-diameter s-SWCNTs.

    View details for DOI 10.1002/smll.201403761

    View details for Web of Science ID 000356444600014

  • Nickel-coated silicon photocathode for water splitting in alkaline electrolytes NANO RESEARCH Feng, J., Gong, M., Kenney, M. J., Wu, J. Z., Zhang, B., Li, Y., Dai, H. 2015; 8 (5): 1577-1583
  • An ultrafast rechargeable aluminium-ion battery. Nature Lin, M., Gong, M., Lu, B., Wu, Y., Wang, D., Guan, M., Angell, M., Chen, C., Yang, J., Hwang, B., Dai, H. 2015; 520 (7547): 325-328

    Abstract

    The development of new rechargeable battery systems could fuel various energy applications, from personal electronics to grid storage. Rechargeable aluminium-based batteries offer the possibilities of low cost and low flammability, together with three-electron-redox properties leading to high capacity. However, research efforts over the past 30 years have encountered numerous problems, such as cathode material disintegration, low cell discharge voltage (about 0.55 volts; ref. 5), capacitive behaviour without discharge voltage plateaus (1.1-0.2 volts or 1.8-0.8 volts) and insufficient cycle life (less than 100 cycles) with rapid capacity decay (by 26-85 per cent over 100 cycles). Here we present a rechargeable aluminium battery with high-rate capability that uses an aluminium metal anode and a three-dimensional graphitic-foam cathode. The battery operates through the electrochemical deposition and dissolution of aluminium at the anode, and intercalation/de-intercalation of chloroaluminate anions in the graphite, using a non-flammable ionic liquid electrolyte. The cell exhibits well-defined discharge voltage plateaus near 2 volts, a specific capacity of about 70 mA h g(-1) and a Coulombic efficiency of approximately 98 per cent. The cathode was found to enable fast anion diffusion and intercalation, affording charging times of around one minute with a current density of ~4,000 mA g(-1) (equivalent to ~3,000 W kg(-1)), and to withstand more than 7,500 cycles without capacity decay.

    View details for DOI 10.1038/nature14340

    View details for PubMedID 25849777

  • Highly Active and Stable Hybrid Catalyst of Cobalt-Doped FeS2 Nanosheets-Carbon Nanotubes for Hydrogen Evolution Reaction JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Wang, D., Gong, M., Chou, H., Pan, C., Chen, H., Wu, Y., Lin, M., Guan, M., Yang, J., Chen, C., Wang, Y., Hwang, B., Chen, C., Dai, H. 2015; 137 (4): 1587-1592

    Abstract

    Hydrogen evolution reaction (HER) from water through electrocatalysis using cost-effective materials to replace precious Pt catalysts holds great promise for clean energy technologies. In this work we developed a highly active and stable catalyst containing Co doped earth abundant iron pyrite FeS2 nanosheets hybridized with carbon nanotubes (Fe1-xCoxS2/CNT hybrid catalysts) for HER in acidic solutions. The pyrite phase of Fe1-xCoxS2/CNT was characterized by powder X-ray diffraction and absorption spectroscopy. Electrochemical measurements showed a low overpotential of ∼0.12 V at 20 mA/cm(2), small Tafel slope of ∼46 mV/decade, and long-term durability over 40 h of HER operation using bulk quantities of Fe0.9Co0.1S2/CNT hybrid catalysts at high loadings (∼7 mg/cm(2)). Density functional theory calculation revealed that the origin of high catalytic activity stemmed from a large reduction of the kinetic energy barrier of H atom adsorption on FeS2 surface upon Co doping in the iron pyrite structure. It is also found that the high HER catalytic activity of Fe0.9Co0.1S2 hinges on the hybridization with CNTs to impart strong heteroatomic interactions between CNT and Fe0.9Co0.1S2. This work produces the most active HER catalyst based on iron pyrite, suggesting a scalable, low cost, and highly efficient catalyst for hydrogen generation.

    View details for DOI 10.1021/ja511572q

    View details for Web of Science ID 000349138600034

  • Graphene Nanoribbons Under Mechanical Strain ADVANCED MATERIALS Chen, C., Wu, J. Z., Lam, K. T., Hong, G., Gong, M., Zhang, B., Lu, Y., Antaris, A. L., Diao, S., Guo, J., Dai, H. 2015; 27 (2): 303-309

    Abstract

    Uniaxial strains are introduced into individual graphene nanoribbons (GNRs) with highly smooth edges to investigate the strain effects on Raman spectroscopic and electrical properties of GNRs. It is found that uniaxial strain downshifts the Raman G-band frequency of GNRs linearly and tunes their bandgap significantly in a non-monotonic manner. The strain engineering of GNRs is promising for potential electronics and photonics applications.

    View details for DOI 10.1002/adma.201403750

    View details for Web of Science ID 000347698300018

    View details for PubMedID 25355690

  • A mini review of NiFe-based materials as highly active oxygen evolution reaction electrocatalysts NANO RESEARCH Gong, M., Dai, H. 2015; 8 (1): 23-39
  • Top-Down Patterning and Self-Assembly for Regular Arrays of Semiconducting Single-Walled Carbon Nanotubes ADVANCED MATERIALS Wu, J., Antaris, A., Gong, M., Dai, H. 2014; 26 (35): 6151-?
  • Through-skull fluorescence imaging of the brain in a new near-infrared window NATURE PHOTONICS Hong, G., Diao, S., Chang, J., Antaris, A. L., Chen, C., Zhang, B., Zhao, S., Atochin, D. N., Huang, P. L., Andreasson, K. I., Kuo, C. J., Dai, H. 2014; 8 (9): 723-730
  • Tumor Metastasis Inhibition by Imaging-Guided Photothermal Therapy with Single-Walled Carbon Nanotubes ADVANCED MATERIALS Liang, C., Diao, S., Wang, C., Gong, H., Liu, T., Hong, G., Shi, X., Dai, H., Liu, Z. 2014; 26 (32): 5646-?

    Abstract

    Multi-modal imaging guided photothermal therapy with single-walled carbon nanotubes affords effective destruction of primary tumors together with cancer cells in sentinel lymph nodes. This results in remarkably prolonged mouse survival compared to mice treated by elimination of only the primary tumor by either surgery or conventional photothermal therapy.

    View details for DOI 10.1002/adma.201401825

    View details for Web of Science ID 000340900800007

    View details for PubMedID 24924258

  • Recent advances in zinc-air batteries CHEMICAL SOCIETY REVIEWS Li, Y., Dai, H. 2014; 43 (15): 5257-5275

    Abstract

    Zinc-air is a century-old battery technology but has attracted revived interest recently. With larger storage capacity at a fraction of the cost compared to lithium-ion, zinc-air batteries clearly represent one of the most viable future options to powering electric vehicles. However, some technical problems associated with them have yet to be resolved. In this review, we present the fundamentals, challenges and latest exciting advances related to zinc-air research. Detailed discussion will be organized around the individual components of the system - from zinc electrodes, electrolytes, and separators to air electrodes and oxygen electrocatalysts in sequential order for both primary and electrically/mechanically rechargeable types. The detrimental effect of CO2 on battery performance is also emphasized, and possible solutions summarized. Finally, other metal-air batteries are briefly overviewed and compared in favor of zinc-air.

    View details for DOI 10.1039/c4cs00015c

    View details for Web of Science ID 000339306800009

    View details for PubMedID 24926965

  • A plasmonic chip for biomarker discovery and diagnosis of type 1 diabetes NATURE MEDICINE Zhang, B., Kumar, R. B., Dai, H., Feldman, B. J. 2014; 20 (8): 948-953

    Abstract

    Type 1 diabetes (T1D) is an autoimmune disease, whereas type 2 diabetes (T2D) results from insulin resistance and beta cell dysfunction. Previously, the onset of these two separate diseases was easily distinguished, with children being most at risk for T1D and T2D occurring in overweight adults. However, the dramatic rise in obesity, coupled with the notable increase in T1D, has created a large overlap in these previously discrete patient populations. Delayed diagnosis of T1D can result in severe illness or death, and rapid diagnosis of T1D is critical for the efficacy of emerging therapies. However, attempts to apply next-generation platforms have been unsuccessful for detecting diabetes biomarkers. Here we describe the development of a plasmonic gold chip for near-infrared fluorescence-enhanced (NIR-FE) detection of islet cell-targeting autoantibodies. We demonstrate that this platform has high sensitivity and specificity for the diagnosis of T1D and can be used to discover previously unknown biomarkers of T1D.

    View details for DOI 10.1038/nm.3619

    View details for Web of Science ID 000340074600028

    View details for PubMedID 25038825

  • Nanoscale nickel oxide/nickel heterostructures for active hydrogen evolution electrocatalysis NATURE COMMUNICATIONS Gong, M., Zhou, W., Tsai, M., Zhou, J., Guan, M., Lin, M., Zhang, B., Hu, Y., Wang, D., Yang, J., Pennycook, S. J., Hwang, B., Dai, H. 2014; 5

    View details for DOI 10.1038/ncomms5695

    View details for Web of Science ID 000341078500001

  • Ultrathin WS2 Nanoflakes as a High-Performance Electrocatalyst for the Hydrogen Evolution Reaction ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Cheng, L., Huang, W., Gong, Q., Liu, C., Liu, Z., Li, Y., Dai, H. 2014; 53 (30): 7860-7863

    Abstract

    Much has been done to search for highly efficient and inexpensive electrocatalysts for the hydrogen evolution reaction (HER), which is critical to a range of electrochemical and photoelectrochemical processes. A new, high-temperature solution-phase method for the synthesis of ultrathin WS2 nanoflakes is now reported. The resulting product possesses monolayer thickness with dimensions in the nanometer range and abundant edges. These favorable structural features render the WS2 nanoflakes highly active and durable catalysts for the HER in acids. The catalyst exhibits a small HER overpotential of approximately 100 mV and a Tafel slope of 48 mV/decade. These ultrathin WS2 nanoflakes represent an attractive alternative to the precious platinum benchmark catalyst and rival MoS2 materials that have recently been heavily scrutinized for the electrocatalytic HER.

    View details for DOI 10.1002/anie.201402315

    View details for Web of Science ID 000339562400030

    View details for PubMedID 24838978

  • Ultrafast fluorescence imaging in vivo with conjugated polymer fluorophores in the second near-infrared window NATURE COMMUNICATIONS Hong, G., Zou, Y., Antaris, A. L., Diao, S., Wu, D., Cheng, K., Zhang, X., Chen, C., Liu, B., He, Y., Wu, J. Z., Yuan, J., Zhang, B., Tao, Z., Fukunaga, C., Dai, H. 2014; 5

    View details for DOI 10.1038/ncomms5206

    View details for Web of Science ID 000338839100002

  • Ultrafast high-capacity NiZn battery with NiAlCo-layered double hydroxide ENERGY & ENVIRONMENTAL SCIENCE Gong, M., Li, Y., Zhang, H., Zhang, B., Zhou, W., Feng, J., Wang, H., Liang, Y., Fan, Z., Liu, J., Dai, H. 2014; 7 (6): 2025-2032

    View details for DOI 10.1039/c4ee00317a

    View details for Web of Science ID 000336831700026

  • Ly108 expression distinguishes subsets of invariant NKT cells that help autoantibody production and secrete IL-21 from those that secrete IL-17 in lupus prone NZB/W mice JOURNAL OF AUTOIMMUNITY Tang, X., Zhang, B., Jarrell, J. A., Price, J. V., Dai, H., Utz, P. J., Strober, S. 2014; 50: 87-98

    Abstract

    Lupus is a systemic autoimmune disease characterized by anti-nuclear antibodies in humans and genetically susceptible NZB/W mice that can cause immune complex glomerulonephritis. T cells contribute to lupus pathogenesis by secreting pro-inflammatory cytokines such as IL-17, and by interacting with B cells and secreting helper factors such as IL-21 that promote production of IgG autoantibodies. In the current study, we determined whether purified NKT cells or far more numerous conventional non-NKT cells in the spleen of NZB/W female mice secrete IL-17 and/or IL-21 after TCR activation in vitro, and provide help for spontaneous IgG autoantibody production by purified splenic CD19(+) B cells. Whereas invariant NKT cells secreted large amounts of IL-17 and IL-21, and helped B cells, non-NKT cells did not. The subset of IL-17 secreting NZB/W NKT cells expressed the Ly108(lo)CD4(-)NK1.1(-) phenotype, whereas the IL-21 secreting subset expressed the Ly108(hi)CD4(+)NK1.1(-) phenotype and helped B cells secrete a variety of IgG anti-nuclear antibodies. α-galactocylceramide enhanced the helper activity of NZB/W and B6.Sle1b NKT cells for IgG autoantibody secretion by syngeneic B cells. In conclusion, different subsets of iNKT cells from mice with genetic susceptibility to lupus can contribute to pathogenesis by secreting pro-inflammatory cytokines and helping autoantibody production.

    View details for DOI 10.1016/j.jaut.2014.01.002

    View details for Web of Science ID 000336114600012

    View details for PubMedID 24508410

  • Near-infrared II fluorescence for imaging hindlimb vessel regeneration with dynamic tissue perfusion measurement. Circulation. Cardiovascular imaging Hong, G., Lee, J. C., Jha, A., Diao, S., Nakayama, K. H., Hou, L., Doyle, T. C., Robinson, J. T., Antaris, A. L., Dai, H., Cooke, J. P., Huang, N. F. 2014; 7 (3): 517-525

    Abstract

    Real-time vascular imaging that provides both anatomic and hemodynamic information could greatly facilitate the diagnosis of vascular diseases and provide accurate assessment of therapeutic effects. Here, we have developed a novel fluorescence-based all-optical method, named near-infrared II (NIR-II) fluorescence imaging, to image murine hindlimb vasculature and blood flow in an experimental model of peripheral arterial disease, by exploiting fluorescence in the NIR-II region (1000-1400 nm) of photon wavelengths.Because of the reduced photon scattering of NIR-II fluorescence compared with traditional NIR fluorescence imaging and thus much deeper penetration depth into the body, we demonstrated that the mouse hindlimb vasculature could be imaged with higher spatial resolution than in vivo microscopic computed tomography. Furthermore, imaging during 26 days revealed a significant increase in hindlimb microvascular density in response to experimentally induced ischemia within the first 8 days of the surgery (P<0.005), which was confirmed by histological analysis of microvascular density. Moreover, the tissue perfusion in the ischemic hindlimb could be quantitatively measured by the dynamic NIR-II method, revealing the temporal kinetics of blood flow recovery that resembled microbead-based blood flowmetry and laser Doppler blood spectroscopy.The penetration depth of millimeters, high spatial resolution, and fast acquisition rate of NIR-II imaging make it a useful imaging tool for murine models of vascular disease.

    View details for DOI 10.1161/CIRCIMAGING.113.000305

    View details for PubMedID 24657826

  • Near-Infrared II Fluorescence for Imaging Hindlimb Vessel Regeneration With Dynamic Tissue Perfusion Measurement CIRCULATION-CARDIOVASCULAR IMAGING Hong, G., Lee, J. C., Jha, A., Diao, S., Nakayama, K. H., Hou, L., Doyle, T. C., Robinson, J. T., Antaris, A. L., Dai, H., Cooke, J. P., Huang, N. F. 2014; 7 (3): 517-U150
  • Graphite Oxide Nanoparticles with Diameter Greater than 20 nm Are Biocompatible with Mouse Embryonic Stem Cells and Can Be Used in a Tissue Engineering System SMALL Wang, I. E., Robinson, J. T., Do, G., Hong, G., Gould, D. R., Dai, H., Yang, P. C. 2014; 10 (8): 1479-1484

    Abstract

    Graphite oxide sheets demonstrate size-dependent uptake and toxicity towards embryonic stem cells. Graphite oxide sheets larger than 20 nm are biocompatible and can be safely used with mouse embryonic stem cells, while graphite oxide sheets smaller than 20 nm in diameter reduced cell proliferation and increased cell toxicity.

    View details for DOI 10.1002/smll.201303133

    View details for Web of Science ID 000334280500005

    View details for PubMedID 24376186

  • Dependence of the Absorption and Optical Surface Plasmon Scattering of MoS2 Nanoparticles on Aspect Ratio, Size, and Media ACS NANO Yadgarov, L., Choi, C. L., Sedova, A., Cohen, A., Rosentsveig, R., Bar-Elli, O., Oron, D., Dai, H., Tenne, R. 2014; 8 (4): 3575-3583

    Abstract

    The optical and electronic properties of suspensions of inorganic fullerene-like nanoparticles of MoS2 are studied through light absorption and zeta-potential measurements and compared to those of the corresponding microscopic platelets. The total extinction measurements show that, in addition to excitonic peaks and the indirect band gap transition, a new peak is observed at 700-800 nm. This spectral peak has not been reported previously for MoS2. Comparison of the total extinction and decoupled absorption spectrum indicates that this peak largely originates from scattering. Furthermore, the dependence of this peak on nanoparticle size, shape, and surface charge, as well as solvent refractive index, suggests that this transition arises from a plasmon resonance.

    View details for DOI 10.1021/nn5000354

    View details for Web of Science ID 000334990600049

    View details for PubMedID 24669749

  • Fe-N bonding in a carbon nanotube-graphene complex for oxygen reduction: an XAS study PHYSICAL CHEMISTRY CHEMICAL PHYSICS Zhou, J., Duchesne, P. N., Hu, Y., Wang, J., Zhang, P., Li, Y., Regier, T., Dai, H. 2014; 16 (30): 15787-15791

    Abstract

    The electronic structure study of carbon nanotube-graphene complexes has been performed using comprehensive X-ray absorption spectroscopy (XAS) at Fe L- and K-edges, along with C, N and O K-edges. The results obtained from the study of an iron-containing carbon nanotube-graphene complex (NT-G) have been compared in great detail with those of an iron-free carbon nanotube-graphene complex (pNT-G) and iron phthalocyanine (FePc). It has been confirmed that complex-like Fe(3+) in a high spin state is the major iron component in NT-G. The C and N K-edge XANES further confirmed that Fe is very likely to be bonded to N in NT-G. This Fe-N species should be the active site for enhanced oxygen reduction reaction (ORR) activity in NT-G. A unique O K-edge X-ray absorption spectroscopic feature has been observed in NT-G, which might be caused by chemisorbed O2 on the Fe-N site. Such knowledge is important for the understanding of this specific complex, and the knowledge should benefit the rational design of other carbon/metal/nitrogen-containing ORR catalysts with further improved performance.

    View details for DOI 10.1039/c4cp01455c

    View details for Web of Science ID 000339628400006

    View details for PubMedID 24963799

  • Ultrafast fluorescence imaging in vivo with conjugated polymer fluorophores in the second near-infrared window. Nature communications Hong, G., Zou, Y., Antaris, A. L., Diao, S., Wu, D., Cheng, K., Zhang, X., Chen, C., Liu, B., He, Y., Wu, J. Z., Yuan, J., Zhang, B., Tao, Z., Fukunaga, C., Dai, H. 2014; 5: 4206-?

    Abstract

    In vivo fluorescence imaging in the second near-infrared window (1.0-1.7 μm) can afford deep tissue penetration and high spatial resolution, owing to the reduced scattering of long-wavelength photons. Here we synthesize a series of low-bandgap donor/acceptor copolymers with tunable emission wavelengths of 1,050-1,350 nm in this window. Non-covalent functionalization with phospholipid-polyethylene glycol results in water-soluble and biocompatible polymeric nanoparticles, allowing for live cell molecular imaging at >1,000 nm with polymer fluorophores for the first time. Importantly, the high quantum yield of the polymer allows for in vivo, deep-tissue and ultrafast imaging of mouse arterial blood flow with an unprecedented frame rate of >25 frames per second. The high time-resolution results in spatially and time resolved imaging of the blood flow pattern in cardiogram waveform over a single cardiac cycle (~200 ms) of a mouse, which has not been observed with fluorescence imaging in this window before.

    View details for DOI 10.1038/ncomms5206

    View details for PubMedID 24947309

  • Nanoscale nickel oxide/nickel heterostructures for active hydrogen evolution electrocatalysis. Nature communications Gong, M., Zhou, W., Tsai, M., Zhou, J., Guan, M., Lin, M., Zhang, B., Hu, Y., Wang, D., Yang, J., Pennycook, S. J., Hwang, B., Dai, H. 2014; 5: 4695-?

    Abstract

    Active, stable and cost-effective electrocatalysts are a key to water splitting for hydrogen production through electrolysis or photoelectrochemistry. Here we report nanoscale nickel oxide/nickel heterostructures formed on carbon nanotube sidewalls as highly effective electrocatalysts for hydrogen evolution reaction with activity similar to platinum. Partially reduced nickel interfaced with nickel oxide results from thermal decomposition of nickel hydroxide precursors bonded to carbon nanotube sidewalls. The metal ion-carbon nanotube interactions impede complete reduction and Ostwald ripening of nickel species into the less hydrogen evolution reaction active pure nickel phase. A water electrolyzer that achieves ~20 mA cm(-2) at a voltage of 1.5 V, and which may be operated by a single-cell alkaline battery, is fabricated using cheap, non-precious metal-based electrocatalysts.

    View details for DOI 10.1038/ncomms5695

    View details for PubMedID 25146255

  • Plasmonic micro-beads for fluorescence enhanced, multiplexed protein detection with flow cytometry CHEMICAL SCIENCE Zhang, B., Yang, J., Zou, Y., Gong, M., Chen, H., Hong, G., Antaris, A. L., Li, X., Liu, C., Chen, C., Dai, H. 2014; 5 (10): 4070-4075

    View details for DOI 10.1039/c4sc01206b

    View details for Web of Science ID 000341195100048

  • Self-Assembly of Semiconducting Single-Walled Carbon Nanotubes into Dense, Aligned Rafts SMALL Wu, J., Jiao, L., Antaris, A., Choi, C. L., Xie, L., Wu, Y., Diao, S., Chen, C., Chen, Y., Dai, H. 2013; 9 (24): 4142-4148

    Abstract

    Highly pure semiconducting single-walled carbon nanotubes (SWNTs) are separated from bulk materials and self-assembled into densely aligned rafts. Microscopy and spectroscopy reveals ∼100 SWNTs per micrometer within the rafts. Short channel field-effect transistors (FETs) from tens of purely semiconducting SWNTs within a submicrometer channel width achieve unprecedented on-currents (up to 121 μA) with high on/off ratios. The results demonstrate densely aligned semiconducting SWNTs for high-performance nanoelectronics.

    View details for DOI 10.1002/smll.201301547

    View details for Web of Science ID 000328453300008

    View details for PubMedID 23843273

  • Biological Imaging Using Nanoparticles of Small Organic Molecules with Fluorescence Emission at Wavelengths Longer than 1000 nm ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Tao, Z., Hong, G., Shinji, C., Chen, C., Diao, S., Antaris, A. L., Zhang, B., Zou, Y., Dai, H. 2013; 52 (49): 13002-13006

    Abstract

    Embedded in a polymer: A hydrophobic organic molecule that fluoresces in the near-infrared II (NIR-II) region was made water-soluble and biocompatible by its embedment in a polymer nanoparticle, which was then coated with hydrophilic poly(ethylene glycol) chains. The resulting nanoparticles exhibit bright fluorescence in the NIR-II window and high photostability in aqueous media and were used for in vivo imaging in mice.

    View details for DOI 10.1002/anie.201307346

    View details for Web of Science ID 000327410300044

  • WS2 nanoflakes from nanotubes for electrocatalysis NANO RESEARCH Choi, C. L., Feng, J., Li, Y., Wu, J., Zak, A., Tenne, R., Dai, H. 2013; 6 (12): 921-928
  • High-Performance Silicon Photoanodes Passivated with Ultrathin Nickel Films for Water Oxidation SCIENCE Kenney, M. J., Gong, M., Li, Y., Wu, J. Z., Feng, J., Lanza, M., Dai, H. 2013; 342 (6160): 836-840

    Abstract

    Silicon's sensitivity to corrosion has hindered its use in photoanode applications. We found that deposition of a ~2-nanometer nickel film on n-type silicon (n-Si) with its native oxide affords a high-performance metal-insulator-semiconductor photoanode for photoelectrochemical (PEC) water oxidation in both aqueous potassium hydroxide (KOH, pH = 14) and aqueous borate buffer (pH = 9.5) solutions. The Ni film acted as a surface protection layer against corrosion and as a nonprecious metal electrocatalyst for oxygen evolution. In 1 M aqueous KOH, the Ni/n-Si photoanodes exhibited high PEC activity with a low onset potential (~1.07 volts versus reversible hydrogen electrode), high photocurrent density, and durability. The electrode showed no sign of decay after ~80 hours of continuous PEC water oxidation in a mixed lithium borate-potassium borate electrolyte. The high photovoltage was attributed to a high built-in potential in a metal-insulator-semiconductor-like device with an ultrathin, incomplete screening Ni/NiO(x) layer from the electrolyte.

    View details for DOI 10.1126/science.1241327

    View details for Web of Science ID 000326923000032

    View details for PubMedID 24233719

  • HREM analysis of graphite-encapsulated metallic nanoparticles for possible medical applications ULTRAMICROSCOPY Sinclair, R., Li, H., Madsen, S., Dai, H. 2013; 134: 167-174

    Abstract

    High resolution electron microscopy has been applied to study the structure of metallic nanoparticles. These have sparked considerable interest as contrast agents in the field of biological imaging, including in magnetic resonance imaging (MRI) and computed tomography (CT). Here, we describe a method of synthesizing sub-10nm superparamagnetic metal and alloy nanoparticles by reduction of metallic salts. Annealing at 900°C in a methane/hydrogen environment forms a thin graphitic-carbon shell which is expected to improve stability, biocompatibility, and functionalization. Subsequent high resolution electron microscopy verifies graphitization and allows for crystallographic analysis. Most particles consist of single crystals in the phase predicted for the bulk material at the annealing temperature. Electron energy loss spectroscopy, energy dispersive X-ray spectroscopy and lattice constant measurements show large variation in composition for alloy nanoparticles from a single synthesis. The magnetization relaxation time (T2) measurements demonstrate that Fe and AuFe nanoparticles compete with commercially available iron oxide MRI contrast agents. X-ray attenuation measurements of an AuFe alloy nanoparticle solution gave a relative radiodensity of 280 Hounsfield Units, demonstrating promise as a dual-purpose contrast agent in CT and MRI. Long term stability in an atmospheric environment was also tested, with no signs of corrosion or oxidation after several years of storage.

    View details for DOI 10.1016/j.ultramic.2013.05.006

    View details for Web of Science ID 000324474900022

  • An Integrated Peptide-Antigen Microarray on Plasmonic Gold Films for Sensitive Human Antibody Profiling PLOS ONE Zhang, B., Jarrell, J. A., Price, J. V., Tabakman, S. M., Li, Y., Gong, M., Hong, G., Feng, J., Utz, P. J., Dai, H. 2013; 8 (7)
  • An Advanced Ni-Fe Layered Double Hydroxide Electrocatalyst for Water Oxidation JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Gong, M., Li, Y., Wang, H., Liang, Y., Wu, J. Z., Zhou, J., Wang, J., Regier, T., Wei, F., Dai, H. 2013; 135 (23): 8452-8455

    Abstract

    Highly active, durable, and cost-effective electrocatalysts for water oxidation to evolve oxygen gas hold a key to a range of renewable energy solutions, including water-splitting and rechargeable metal-air batteries. Here, we report the synthesis of ultrathin nickel-iron layered double hydroxide (NiFe-LDH) nanoplates on mildly oxidized multiwalled carbon nanotubes (CNTs). Incorporation of Fe into the nickel hydroxide induced the formation of NiFe-LDH. The crystalline NiFe-LDH phase in nanoplate form is found to be highly active for oxygen evolution reaction in alkaline solutions. For NiFe-LDH grown on a network of CNTs, the resulting NiFe-LDH/CNT complex exhibits higher electrocatalytic activity and stability for oxygen evolution than commercial precious metal Ir catalysts.

    View details for DOI 10.1021/ja4027715

    View details for Web of Science ID 000320483900006

    View details for PubMedID 23701670

  • Biodistribution, pharmacokinetics and toxicology of Ag2S near-infrared quantum dots in mice BIOMATERIALS Zhang, Y., Zhang, Y., Hong, G., He, W., Zhou, K., Yang, K., Li, F., Chen, G., Liu, Z., Dai, H., Wang, Q. 2013; 34 (14): 3639-3646

    Abstract

    Ag2S quantum dots (QDs) have been demonstrated as a promising near-infrared II (NIR-II, 1.0-1.4 ?m) emitting nanoprobe for in vivo imaging and detection. In this work, we carefully study the long-term in vivo biodistribution of Ag2S QDs functionalized with polyethylene glycol (PEG) and systematically examine the potential toxicity of Ag2S QDs over time. Our results show that PEGylated-Ag2S QDs are mainly accumulated in the reticuloendothelial system (RES) including liver and spleen after intravenous administration and can be gradually cleared, mostly by fecal excretion. PEGylated-Ag2S QDs do not cause appreciable toxicity at our tested doses (15 and 30 mg/kg) to the treated mice over a period of 2 months as evidenced by blood biochemistry, hematological analysis and histological examinations. Our work lays a solid foundation for further biomedical applications of Ag2S QDs as an important in vivo imaging agent in the NIR-II region.

    View details for DOI 10.1016/j.biomaterials.2013.01.089

    View details for Web of Science ID 000317534200010

    View details for PubMedID 23415643

  • Advanced zinc-air batteries based on high-performance hybrid electrocatalysts NATURE COMMUNICATIONS Li, Y., Gong, M., Liang, Y., Feng, J., Kim, J., Wang, H., Hong, G., Zhang, B., Dai, H. 2013; 4

    View details for DOI 10.1038/ncomms2812

    View details for Web of Science ID 000320589900001

  • High-resolution, serial intravital microscopic imaging of nanoparticle delivery and targeting in a small animal tumor model NANO TODAY Smith, B. R., Zavaleta, C., Rosenberg, J., Tong, R., Ramunas, J., Liu, Z., Dai, H., Gambhir, S. S. 2013; 8 (2): 126-137
  • Ultra-Low Doses of Chirality Sorted (6,5) Carbon Nanotubes for Simultaneous Tumor Imaging and Photothermal Therapy ACS NANO Antaris, A. L., Robinson, J. T., Yaghi, O. K., Hong, G., Diao, S., Luong, R., Dai, H. 2013; 7 (4): 3644-3652

    Abstract

    Single-walled carbon nanotubes (SWCNTs) exhibit intrinsic fluorescence and strong optical absorption in the near-infrared (NIR) biological window (0.7-1.4 μm), rendering them ideal for in vivo imaging and photothermal therapy. Advances in SWCNT sorting have led to improved nanoelectronics and are promising for nanomedicine. To date, SWCNTs used in vivo consist of heterogeneous mixtures of nanotubes and only a small subset of chirality nanotubes fluoresces or heats under a NIR laser. Here, we demonstrate that separated (6,5) SWCNTs exchanged into a biocompatible surfactant, C18-PMH-mPEG, are more than 6-fold brighter in photoluminescence on the per mass basis, afford clear tumor imaging, and reach requisite photothermal tumor ablation temperatures with a >10-fold lower injected dose than as-synthesized SWCNT mixtures while exhibiting relatively low (6,5) accumulation in the reticuloendothelial system. The intravenous injection of ∼4 μg of (6,5) SWCNTs per mouse (0.254 mg/kg) for dual imaging/photothermal therapy is, by far, the lowest reported dose for nanoparticle-based in vivo therapeutics.

    View details for DOI 10.1021/nn4006472

    View details for Web of Science ID 000318143300081

    View details for PubMedID 23521224

  • Strongly Coupled lnorganic/Nanocarbon Hybrid Materials for Advanced Electrocatalysis JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Liang, Y., Li, Y., Wang, H., Dai, H. 2013; 135 (6): 2013-2036

    Abstract

    Electrochemical systems, such as fuel cell and water splitting devices, represent some of the most efficient and environmentally friendly technologies for energy conversion and storage. Electrocatalysts play key roles in the chemical processes but often limit the performance of the entire systems due to insufficient activity, lifetime, or high cost. It has been a long-standing challenge to develop efficient and durable electrocatalysts at low cost. In this Perspective, we present our recent efforts in developing strongly coupled inorganic/nanocarbon hybrid materials to improve the electrocatalytic activities and stability of inorganic metal oxides, hydroxides, sulfides, and metal-nitrogen complexes. The hybrid materials are synthesized by direct nucleation, growth, and anchoring of inorganic nanomaterials on the functional groups of oxidized nanocarbon substrates including graphene and carbon nanotubes. This approach affords strong chemical attachment and electrical coupling between the electrocatalytic nanoparticles and nanocarbon, leading to nonprecious metal-based electrocatalysts with improved activity and durability for the oxygen reduction reaction for fuel cells and chlor-alkali catalysis, oxygen evolution reaction, and hydrogen evolution reaction. X-ray absorption near-edge structure and scanning transmission electron microscopy are employed to characterize the hybrids materials and reveal the coupling effects between inorganic nanomaterials and nanocarbon substrates. Z-contrast imaging and electron energy loss spectroscopy at single atom level are performed to investigate the nature of catalytic sites on ultrathin graphene sheets. Nanocarbon-based hybrid materials may present new opportunities for the development of electrocatalysts meeting the requirements of activity, durability, and cost for large-scale electrochemical applications.

    View details for DOI 10.1021/ja3089923

    View details for Web of Science ID 000315080100001

    View details for PubMedID 23339685

  • Multiplexed cytokine detection on plasmonic gold substrates with enhanced near-infrared fluorescence NANO RESEARCH Zhang, B., Price, J., Hong, G., Tabakman, S. M., Wang, H., Jarrell, J. A., Feng, J., Utz, P. J., Dai, H. 2013; 6 (2): 113-120
  • Single-Walled Carbon Nanotube Surface Control of Complement Recognition and Activation ACS NANO Andersen, A. J., Robinson, J. T., Dai, H., Hunter, A. C., Andresen, T. L., Moghimi, S. M. 2013; 7 (2): 1108-1119

    Abstract

    Carbon nanotubes (CNTs) are receiving considerable attention in site-specific drug and nucleic acid delivery, photodynamic therapy, and photoacoustic molecular imaging. Despite these advances, nanotubes may activate the complement system (an integral part of innate immunity), which can induce clinically significant anaphylaxis. We demonstrate that single-walled CNTs coated with human serum albumin activate the complement system through C1q-mediated classical and the alternative pathways. Surface coating with methoxypoly(ethylene glycol)-based amphiphiles, which confers solubility and prolongs circulation profiles of CNTs, activates the complement system differently, depending on the amphiphile structure. CNTs with linear poly(ethylene glycol) amphiphiles trigger the lectin pathway of the complement through both L-ficolin and mannan-binding lectin recognition. The lectin pathway activation, however, did not trigger the amplification loop of the alternative pathway. An amphiphile with branched poly(ethylene glycol) architecture also activated the lectin pathway but only through L-ficolin recognition. Importantly, this mode of activation neither generated anaphylatoxins nor induced triggering of the effector arm of the complement system. These observations provide a major step toward nanomaterial surface modification with polymers that have the properties to significantly improve innate immunocompatibility by limiting the formation of complement C3 and C5 convertases.

    View details for DOI 10.1021/nn3055175

    View details for Web of Science ID 000315618700027

    View details for PubMedID 23301860

  • Advanced zinc-air batteries based on high-performance hybrid electrocatalysts. Nature communications Li, Y., Gong, M., Liang, Y., Feng, J., Kim, J., Wang, H., Hong, G., Zhang, B., Dai, H. 2013; 4: 1805-?

    Abstract

    Primary and rechargeable Zn-air batteries could be ideal energy storage devices with high energy and power density, high safety and economic viability. Active and durable electrocatalysts on the cathode side are required to catalyse oxygen reduction reaction during discharge and oxygen evolution reaction during charge for rechargeable batteries. Here we developed advanced primary and rechargeable Zn-air batteries with novel CoO/carbon nanotube hybrid oxygen reduction catalyst and Ni-Fe-layered double hydroxide oxygen evolution catalyst for the cathode. These catalysts exhibited higher catalytic activity and durability in concentrated alkaline electrolytes than precious metal Pt and Ir catalysts. The resulting primary Zn-air battery showed high discharge peak power density ~265 mW cm(-2), current density ~200 mA cm(-2) at 1 V and energy density >700 Wh kg(-1). Rechargeable Zn-air batteries in a tri-electrode configuration exhibited an unprecedented small charge-discharge voltage polarization of ~0.70 V at 20 mA cm(-2), high reversibility and stability over long charge and discharge cycles.

    View details for DOI 10.1038/ncomms2812

    View details for PubMedID 23651993

  • Imaging state of charge and its correlation to interaction variation in an LiMn0.75Fe0.25PO4 nanorods-graphene hybrid CHEMICAL COMMUNICATIONS Zhou, J., Wang, J., Hu, Y., Regier, T., Wang, H., Yang, Y., Cui, Y., Dai, H. 2013; 49 (17): 1765-1767

    Abstract

    Visualization of the state of charge (SOC) in an LiMn(0.75)Fe(0.25)PO(4) nanorods-graphene hybrid nanostructure (LMFP-C) is realized by chemical mapping of the Fe valance state using scanning transmission X-ray microscopy (STXM). The LMFP-graphene interaction strength variation studied by C K-edge STXM has been correlated to SOC variation, i.e. a stronger interaction was observed for sample regions with a higher SOC in LMFP. Such structure-performance correlation opens new perspectives for a rational design of a better performance olivine cathode for lithium ion batteries.

    View details for DOI 10.1039/c3cc39015b

    View details for Web of Science ID 000314424700025

    View details for PubMedID 23340608

  • Experimentally Engineering the Edge Termination of Graphene Nanoribbons ACS NANO Zhang, X., Yazyev, O. V., Feng, J., Xie, L., Tao, C., Chen, Y., Jiao, L., Pedramrazi, Z., Zettl, A., Louie, S. G., Dai, H., Crommie, M. F. 2013; 7 (1): 198-202

    Abstract

    The edges of graphene nanoribbons (GNRs) have attracted much interest due to their potentially strong influence on GNR electronic and magnetic properties. Here we report the ability to engineer the microscopic edge termination of high-quality GNRs via hydrogen plasma etching. Using a combination of high-resolution scanning tunneling microscopy and first-principles calculations, we have determined the exact atomic structure of plasma-etched GNR edges and established the chemical nature of terminating functional groups for zigzag, armchair, and chiral edge orientations. We find that the edges of hydrogen-plasma-etched GNRs are generally flat, free of structural reconstructions, and terminated by hydrogen atoms with no rehybridization of the outermost carbon edge atoms. Both zigzag and chiral edges show the presence of edge states.

    View details for DOI 10.1021/nn303730v

    View details for Web of Science ID 000314082800024

    View details for PubMedID 23194280

  • An integrated peptide-antigen microarray on plasmonic gold films for sensitive human antibody profiling. PloS one Zhang, B., Jarrell, J. A., Price, J. V., Tabakman, S. M., Li, Y., Gong, M., Hong, G., Feng, J., Utz, P. J., Dai, H. 2013; 8 (7)

    Abstract

    High-throughput screening for interactions of peptides with a variety of antibody targets could greatly facilitate proteomic analysis for epitope mapping, enzyme profiling, drug discovery and biomarker identification. Peptide microarrays are suited for such undertaking because of their high-throughput capability. However, existing peptide microarrays lack the sensitivity needed for detecting low abundance proteins or low affinity peptide-protein interactions. This work presents a new peptide microarray platform constructed on nanostructured plasmonic gold substrates capable of metal enhanced NIR fluorescence enhancement (NIR-FE) by hundreds of folds for screening peptide-antibody interactions with ultrahigh sensitivity. Further, an integrated histone peptide and whole antigen array is developed on the same plasmonic gold chip for profiling human antibodies in the sera of systemic lupus erythematosus (SLE) patients, revealing that collectively a panel of biomarkers against unmodified and post-translationally modified histone peptides and several whole antigens allow more accurate differentiation of SLE patients from healthy individuals than profiling biomarkers against peptides or whole antigens alone.

    View details for DOI 10.1371/journal.pone.0071043

    View details for PubMedID 23923050

  • Strongly coupled inorganic-nano-carbon hybrid materials for energy storage CHEMICAL SOCIETY REVIEWS Wang, H., Dai, H. 2013; 42 (7): 3088-3113

    Abstract

    The global shift of energy production from fossil fuels to renewable energy sources requires more efficient and reliable electrochemical energy storage devices. In particular, the development of electric or hydrogen powered vehicles calls for much-higher-performance batteries, supercapacitors and fuel cells than are currently available. In this review, we present an approach to synthesize electrochemical energy storage materials to form strongly coupled hybrids (SC-hybrids) of inorganic nanomaterials and novel graphitic nano-carbon materials such as carbon nanotubes and graphene, through nucleation and growth of nanoparticles at the functional groups of oxidized graphitic nano-carbon. We show that the inorganic-nano-carbon hybrid materials represent a new approach to synthesize electrode materials with higher electrochemical performance than traditional counterparts made by simple physical mixtures of electrochemically active inorganic particles and conducting carbon materials. The inorganic-nano-carbon hybrid materials are novel due to possible chemical bonding between inorganic nanoparticles and oxidized carbon, affording enhanced charge transport and increased rate capability of electrochemical materials without sacrificing specific capacity. Nano-carbon with various degrees of oxidation provides a novel substrate for nanoparticle nucleation and growth. The interactions between inorganic precursors and oxidized-carbon substrates provide a degree of control over the morphology, size and structure of the resulting inorganic nanoparticles. This paper reviews the recent development of inorganic-nano-carbon hybrid materials for electrochemical energy storage and conversion, including the preparation and functionalization of graphene sheets and carbon nanotubes to impart oxygen containing groups and defects, and methods of synthesis of nanoparticles of various morphologies on oxidized graphene and carbon nanotubes. We then review the applications of the SC-hybrid materials for high performance lithium ion batteries, rechargeable Li-S and Li-O2 batteries, supercapacitors and ultrafast Ni-Fe batteries, and new electrocatalysts for oxygen reduction, oxygen evolution and hydrogen evolution reactions.

    View details for DOI 10.1039/c2cs35307e

    View details for Web of Science ID 000316869500026

    View details for PubMedID 23361617

  • Multifunctional in vivo vascular imaging using near-infrared II fluorescence NATURE MEDICINE Hong, G., Lee, J. C., Robinson, J. T., Raaz, U., Xie, L., Huang, N. F., Cooke, J. P., Dai, H. 2012; 18 (12): 1841-?

    Abstract

    In vivo real-time epifluorescence imaging of mouse hind limb vasculatures in the second near-infrared region (NIR-II) is performed using single-walled carbon nanotubes as fluorophores. Both high spatial (?30 ?m) and temporal (<200 ms per frame) resolution for small-vessel imaging are achieved at 1-3 mm deep in the hind limb owing to the beneficial NIR-II optical window that affords deep anatomical penetration and low scattering. This spatial resolution is unattainable by traditional NIR imaging (NIR-I) or microscopic computed tomography, and the temporal resolution far exceeds scanning microscopic imaging techniques. Arterial and venous vessels are unambiguously differentiated using a dynamic contrast-enhanced NIR-II imaging technique on the basis of their distinct hemodynamics. Further, the deep tissue penetration and high spatial and temporal resolution of NIR-II imaging allow for precise quantifications of blood velocity in both normal and ischemic femoral arteries, which are beyond the capabilities of ultrasonography at lower blood velocities.

    View details for DOI 10.1038/nm.2995

    View details for Web of Science ID 000311999800033

    View details for PubMedID 23160236

  • Near infrared imaging and photothermal ablation of vascular inflammation using single-walled carbon nanotubes. Journal of the American Heart Association Kosuge, H., Sherlock, S. P., Kitagawa, T., Dash, R., Robinson, J. T., Dai, H., McConnell, M. V. 2012; 1 (6)

    Abstract

    Macrophages are critical contributors to atherosclerosis. Single-walled carbon nanotubes (SWNTs) show promising properties for cellular imaging and thermal therapy, which may have application to vascular macrophages.In vitro uptake and photothermal destruction of mouse macrophage cells (RAW264.7) were performed with SWNTs (14.7 nmol/L) exposed to an 808-nm light source. SWNTs were taken up by 94 ± 6% of macrophages, and light exposure induced 93 ± 3% cell death. In vivo vascular macrophage uptake and ablation were then investigated in carotid-ligated FVB mice (n=33) after induction of hyperlipidemia and diabetes. Two weeks postligation, near-infrared fluorescence (NIRF) carotid imaging (n=12) was performed with SWNT-Cy5.5 (8 nmol of Cy5.5) given via the tail vein. Photothermal heating and macrophage apoptosis were evaluated on freshly excised carotid arteries (n=21). NIRF of SWNTs showed higher signal intensity in ligated carotids compared with sham, confirmed by both in situ and ex vivo NIRF imaging (P<0.05, ligation versus sham). Immunofluorescence staining showed colocalization of SWNT-Cy5.5 and macrophages in atherosclerotic lesions. Light (808 nm) exposure of freshly excised carotids showed heating and induction of macrophage apoptosis in ligated left carotid arteries with SWNTs, but not in control groups without SWNTs or without light exposure.Carbon nanotubes accumulate in atherosclerotic macrophages in vivo and provide a multifunctional platform for imaging and photothermal therapy of vascular inflammation.

    View details for DOI 10.1161/JAHA.112.002568

    View details for PubMedID 23316318

  • Chirality Enriched (12,1) and (11,3) Single-Walled Carbon Nanotubes for Biological Imaging JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Diao, S., Hong, G., Robinson, J. T., Jiao, L., Antaris, A. L., Wu, J. Z., Choi, C. L., Dai, H. 2012; 134 (41): 16971-16974

    Abstract

    The intrinsic band gap photoluminescence of semiconducting single-walled carbon nanotubes (SWNTs) makes them promising biological imaging probes in the second near-infrared (NIR-II, 1.0-1.4 ?m) window. Thus far, SWNTs used for biological applications have been a complex mixture of metallic and semiconducting species with random chiralities, preventing simultaneous resonant excitation of all semiconducting nanotubes and emission at a single well-defined wavelength. Here, we developed a simple gel filtration method to enrich semiconducting (12,1) and (11,3) SWNTs with identical resonance absorption at ~808 nm and emission near ~1200 nm. The chirality sorted SWNTs showed ~5-fold higher photoluminescence intensity under resonant excitation of 808 nm than unsorted SWNTs on a per-mass basis. Real-time in vivo video imaging of whole mouse body and tumor vessels was achieved using a ~6-fold lower injected dose of (12,1) and (11,3) SWNTs (~3 ?g per mouse or ~0.16 mg/kg of body weight vs 1.0 mg/kg for unsorted SWNTs) than a previous heterogeneous mixture, demonstrating the first resonantly excited and chirality separated SWNTs for biological imaging.

    View details for DOI 10.1021/ja307966u

    View details for Web of Science ID 000309854700014

    View details for PubMedID 23033937

  • Engineering manganese oxide/nanocarbon hybrid materials for oxygen reduction electrocatalysis NANO RESEARCH Feng, J., Liang, Y., Wang, H., Li, Y., Zhang, B., Zhou, J., Wang, J., Regier, T., Dai, H. 2012; 5 (10): 718-725
  • Oxygen Reduction Electrocatalyst Based on Strongly Coupled Cobalt Oxide Nanocrystals and Carbon Nanotubes JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Liang, Y., Wang, H., Diao, P., Chang, W., Hong, G., Li, Y., Gong, M., Xie, L., Zhou, J., Wang, J., Regier, T. Z., Wei, F., Dai, H. 2012; 134 (38): 15849-15857

    Abstract

    Electrocatalyst for oxygen reduction reaction (ORR) is crucial for a variety of renewable energy applications and energy-intensive industries. The design and synthesis of highly active ORR catalysts with strong durability at low cost is extremely desirable but remains challenging. Here, we used a simple two-step method to synthesize cobalt oxide/carbon nanotube (CNT) strongly coupled hybrid as efficient ORR catalyst by directly growing nanocrystals on oxidized multiwalled CNTs. The mildly oxidized CNTs provided functional groups on the outer walls to nucleate and anchor nanocrystals, while retaining intact inner walls for highly conducting network. Cobalt oxide was in the form of CoO due to a gas-phase annealing step in NH(3). The resulting CoO/nitrogen-doped CNT (NCNT) hybrid showed high ORR current density that outperformed Co(3)O(4)/graphene hybrid and commercial Pt/C catalyst at medium overpotential, mainly through a 4e reduction pathway. The metal oxide/carbon nanotube hybrid was found to be advantageous over the graphene counterpart in terms of active sites and charge transport. Last, the CoO/NCNT hybrid showed high ORR activity and stability under a highly corrosive condition of 10 M NaOH at 80 °C, demonstrating the potential of strongly coupled inorganic/nanocarbon hybrid as a novel catalyst system in oxygen depolarized cathode for chlor-alkali electrolysis.

    View details for DOI 10.1021/ja305623m

    View details for Web of Science ID 000309099700042

    View details for PubMedID 22957510

  • Shape Matters: Intravital Microscopy Reveals Surprising Geometrical Dependence for Nanoparticles in Tumor Models of Extravasation NANO LETTERS Smith, B. R., Kempen, P., Bouley, D., Xu, A., Liu, Z., Melosh, N., Dai, H., Sinclair, R., Gambhir, S. S. 2012; 12 (7): 3369-3377

    Abstract

    Delivery is one of the most critical obstacles confronting nanoparticle use in cancer diagnosis and therapy. For most oncological applications, nanoparticles must extravasate in order to reach tumor cells and perform their designated task. However, little understanding exists regarding the effect of nanoparticle shape on extravasation. Herein we use real-time intravital microscopic imaging to meticulously examine how two different nanoparticles behave across three different murine tumor models. The study quantitatively demonstrates that high-aspect ratio single-walled carbon nanotubes (SWNTs) display extravasational behavior surprisingly different from, and counterintuitive to, spherical nanoparticles although the nanoparticles have similar surface coatings, area, and charge. This work quantitatively indicates that nanoscale extravasational competence is highly dependent on nanoparticle geometry and is heterogeneous.

    View details for DOI 10.1021/nl204175t

    View details for Web of Science ID 000306296200004

    View details for PubMedID 22650417

  • Rechargeable Li-O-2 batteries with a covalently coupled MnCo2O4-graphene hybrid as an oxygen cathode catalyst ENERGY & ENVIRONMENTAL SCIENCE Wang, H., Yang, Y., Liang, Y., Zheng, G., Li, Y., Cui, Y., Dai, H. 2012; 5 (7): 7931-7935

    View details for DOI 10.1039/c2ee21746e

    View details for Web of Science ID 000305530900032

  • In Vivo Fluorescence Imaging in the Second Near-Infrared Window with Long Circulating Carbon Nanotubes Capable of Ultrahigh Tumor Uptake JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Robinson, J. T., Hong, G., Liang, Y., Zhang, B., Yaghi, O. K., Dai, H. 2012; 134 (25): 10664-10669

    Abstract

    Cancer imaging requires selective high accumulation of contrast agents in the tumor region and correspondingly low uptake in healthy tissues. Here, by making use of a novel synthetic polymer to solubilize single-walled carbon nanotubes (SWNTs), we prepared a well-functionalized SWNT formulation with long blood circulation (half-life of ?30 h) in vivo to achieve ultrahigh accumulation of ?30% injected dose (ID)/g in 4T1 murine breast tumors in Balb/c mice. Functionalization dependent blood circulation and tumor uptake were investigated through comparisons with phospholipid-PEG solubilized SWNTs. For the first time, we performed video-rate imaging of tumors based on the intrinsic fluorescence of SWNTs in the second near-infrared (NIR-II, 1.1-1.4 ?m) window. We carried out dynamic contrast imaging through principal component analysis (PCA) to immediately pinpoint the tumor within ?20 s after injection. Imaging over time revealed increasing tumor contrast up to 72 h after injection, allowing for its unambiguous identification. The 3D reconstruction of the SWNTs distribution based on their stable photoluminescence inside the tumor revealed a high degree of colocalization of SWNTs and blood vessels, suggesting enhanced permeability and retention (EPR) effect as the main cause of high passive tumor uptake of the nanotubes.

    View details for DOI 10.1021/ja303737a

    View details for Web of Science ID 000305716700052

    View details for PubMedID 22667448

  • Family of Enhanced Photoacoustic Imaging Agents for High-Sensitivity and Multiplexing Studies in Living Mice ACS NANO de la Zerda, A., Bodapati, S., Teed, R., May, S. Y., Tabakman, S. M., Liu, Z., Khuri-Yakub, B. T., Chen, X., Dai, H., Gambhir, S. S. 2012; 6 (6): 4694-4701

    Abstract

    Photoacoustic imaging is a unique modality that overcomes to a great extent the resolution and depth limitations of optical imaging while maintaining relatively high contrast. However, since many diseases will not manifest an endogenous photoacoustic contrast, it is essential to develop exogenous photoacoustic contrast agents that can target diseased tissue(s). Here we present a family of novel photoacoustic contrast agents that are based on the binding of small optical dyes to single-walled carbon nanotubes (SWNT-dye). We synthesized five different SWNT-dye contrast agents using different optical dyes, creating five "flavors" of SWNT-dye nanoparticles. In particular, SWNTs that were coated with either QSY(21) (SWNT-QSY) or indocyanine green (SWNT-ICG) exhibited over 100-times higher photoacoustic contrast in living animals compared to plain SWNTs, leading to subnanomolar sensitivities. We then conjugated the SWNT-dye conjugates with cyclic Arg-Gly-Asp peptides to molecularly target the ?(v)?(3) integrin, which is associated with tumor angiogenesis. Intravenous administration of these tumor-targeted imaging agents to tumor-bearing mice showed significantly higher photoacoustic signal in the tumor than in mice injected with the untargeted contrast agent. Finally, we were able to spectrally separate the photoacoustic signals of SWNT-QSY and SWNT-ICG in living animals injected subcutaneously with both particles in the same location, opening the possibility for multiplexing in vivo studies.

    View details for DOI 10.1021/nn204352r

    View details for Web of Science ID 000305661300017

    View details for PubMedID 22607191

  • An oxygen reduction electrocatalyst based on carbon nanotube-graphene complexes NATURE NANOTECHNOLOGY Li, Y., Zhou, W., Wang, H., Xie, L., Liang, Y., Wei, F., Idrobo, J., Pennycook, S. J., Dai, H. 2012; 7 (6): 394-400

    Abstract

    Oxygen reduction reaction catalysts based on precious metals such as platinum or its alloys are routinely used in fuel cells because of their high activity. Carbon-supported materials containing metals such as iron or cobalt as well as nitrogen impurities have been proposed to increase scalability and reduce costs, but these alternatives usually suffer from low activity and/or gradual deactivation during use. Here, we show that few-walled carbon nanotubes, following outer wall exfoliation via oxidation and high-temperature reaction with ammonia, can act as an oxygen reduction reaction electrocatalyst in both acidic and alkaline solutions. Under a unique oxidation condition, the outer walls of the few-walled carbon nanotubes are partially unzipped, creating nanoscale sheets of graphene attached to the inner tubes. The graphene sheets contain extremely small amounts of irons originated from nanotube growth seeds, and nitrogen impurities, which facilitate the formation of catalytic sites and boost the activity of the catalyst, as revealed by atomic-scale microscopy and electron energy loss spectroscopy. Whereas the graphene sheets formed from the unzipped part of the outer wall of the nanotubes are responsible for the catalytic activity, the inner walls remain intact and retain their electrical conductivity, which facilitates charge transport during electrocatalysis.

    View details for DOI 10.1038/NNANO.2012.72

    View details for Web of Science ID 000305008200014

    View details for PubMedID 22635099

  • Short channel field-effect transistors from highly enriched semiconducting carbon nanotubes NANO RESEARCH Wu, J., Xie, L., Hong, G., Lim, H. E., Thendie, B., Miyata, Y., Shinohara, H., Dai, H. 2012; 5 (6): 388-394
  • An ultrafast nickel-iron battery from strongly coupled inorganic nanoparticle/nanocarbon hybrid materials NATURE COMMUNICATIONS Wang, H., Liang, Y., Gong, M., Li, Y., Chang, W., Mefford, T., Zhou, J., Wang, J., Regier, T., Wei, F., Dai, H. 2012; 3

    Abstract

    Ultrafast rechargeable batteries made from low-cost and abundant electrode materials operating in safe aqueous electrolytes could be attractive for electrochemical energy storage. If both high specific power and energy are achieved, such batteries would be useful for power quality applications such as to assist propelling electric vehicles that require fast acceleration and intense braking. Here we develop a new type of Ni-Fe battery by employing novel inorganic nanoparticle/graphitic nanocarbon (carbon nanotubes and graphene) hybrid materials as electrode materials. We successfully increase the charging and discharging rates by nearly 1,000-fold over traditional Ni-Fe batteries while attaining high energy density. The ultrafast Ni-Fe battery can be charged in ~2 min and discharged within 30 s to deliver a specific energy of 120 Wh kg(-1) and a specific power of 15 kW kg(-1). These features suggest a new generation of Ni-Fe batteries as novel devices for electrochemical energy storage.

    View details for DOI 10.1038/ncomms1921

    View details for Web of Science ID 000306099900044

    View details for PubMedID 22735445

  • Ag2S Quantum Dot: A Bright and Biocompatible Fluorescent Nanoprobe in the Second Near-Infrared Window ACS NANO Zhang, Y., Hong, G., Zhang, Y., Chen, G., Li, F., Dai, H., Wang, Q. 2012; 6 (5): 3695-3702

    Abstract

    Ag(2)S quantum dots (QDs) emitting in the second near-infrared region (NIR-II, 1.0-1.4 ?m) are demonstrated as a promising fluorescent probe with both bright photoluminescence and high biocompatibility for the first time. Highly selective in vitro targeting and imaging of different cell lines are achieved using biocompatible NIR-II Ag(2)S QDs with different targeting ligands. The cytotoxicity study illustrates the Ag(2)S QDs with negligible effects in altering cell proliferation, triggering apoptosis and necrosis, generating reactive oxygen species, and causing DNA damage. Our results have opened up the possibilities of using these biocompatible Ag(2)S QDs for in vivo anatomical imaging and early stage tumor diagnosis with deep tissue penetration, high sensitivity, and elevated spatial and temporal resolution owing to their high emission efficiency in the unique NIR-II imaging window.

    View details for DOI 10.1021/nn301218z

    View details for Web of Science ID 000304231700007

    View details for PubMedID 22515909

  • In Operando X-ray Diffraction and Transmission X-ray Microscopy of Lithium Sulfur Batteries JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Nelson, J., Misra, S., Yang, Y., Jackson, A., Liu, Y., Wang, H., Dai, H., Andrews, J. C., Cui, Y., Toney, M. F. 2012; 134 (14): 6337-6343

    Abstract

    Rechargeable lithium-sulfur (Li-S) batteries hold great potential for high-performance energy storage systems because they have a high theoretical specific energy, low cost, and are eco-friendly. However, the structural and morphological changes during electrochemical reactions are still not well understood. In this Article, these changes in Li-S batteries are studied in operando by X-ray diffraction and transmission X-ray microscopy. We show recrystallization of sulfur by the end of the charge cycle is dependent on the preparation technique of the sulfur cathode. On the other hand, it was found that crystalline Li(2)S does not form at the end of discharge for all sulfur cathodes studied. Furthermore, during cycling the bulk of soluble polysulfides remains trapped within the cathode matrix. Our results differ from previous ex situ results. This highlights the importance of in operando studies and suggests possible strategies to improve cycle life.

    View details for DOI 10.1021/ja2121926

    View details for Web of Science ID 000302524800043

    View details for PubMedID 22432568

  • Densely aligned graphene nanoribbons at similar to 35 nm pitch NANO RESEARCH Jiao, L., Xie, L., Dai, H. 2012; 5 (4): 292-296
  • Covalent Hybrid of Spinel Manganese-Cobalt Oxide and Graphene as Advanced Oxygen Reduction Electrocatalysts JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Liang, Y., Wang, H., Zhou, J., Li, Y., Wang, J., Regier, T., Dai, H. 2012; 134 (7): 3517-3523

    Abstract

    Through direct nanoparticle nucleation and growth on nitrogen doped, reduced graphene oxide sheets and cation substitution of spinel Co(3)O(4) nanoparticles, a manganese-cobalt spinel MnCo(2)O(4)/graphene hybrid was developed as a highly efficient electrocatalyst for oxygen reduction reaction (ORR) in alkaline conditions. Electrochemical and X-ray near-edge structure (XANES) investigations revealed that the nucleation and growth method for forming inorganic-nanocarbon hybrids results in covalent coupling between spinel oxide nanoparticles and N-doped reduced graphene oxide (N-rmGO) sheets. Carbon K-edge and nitrogen K-edge XANES showed strongly perturbed C-O and C-N bonding in the N-rmGO sheet, suggesting the formation of C-O-metal and C-N-metal bonds between N-doped graphene oxide and spinel oxide nanoparticles. Co L-edge and Mn L-edge XANES suggested substitution of Co(3+) sites by Mn(3+), which increased the activity of the catalytic sites in the hybrid materials, further boosting the ORR activity compared with the pure cobalt oxide hybrid. The covalently bonded hybrid afforded much greater activity and durability than the physical mixture of nanoparticles and carbon materials including N-rmGO. At the same mass loading, the MnCo(2)O(4)/N-graphene hybrid can outperform Pt/C in ORR current density at medium overpotentials with stability superior to Pt/C in alkaline solutions.

    View details for DOI 10.1021/ja210924t

    View details for Web of Science ID 000301084700027

    View details for PubMedID 22280461

  • Graphite-Coated Magnetic Nanoparticle Microarray for Few-Cells Enrichment and Detection ACS NANO Chen, Z., Hong, G., Wang, H., Welsher, K., Tabakman, S. M., Sherlock, S. P., Robinson, J. T., Liang, Y., Dai, H. 2012; 6 (2): 1094-1101

    Abstract

    Graphite-coated, highly magnetic FeCo core-shell nanoparticles were synthesized by a chemical vapor deposition method and solubilized in aqueous solution through a unique polymer mixture modification, which significantly improved the biocompatibility and stability of the magnetic nanoparticles (MNPs). Such functionalized MNPs were proven to be very stable in different conditions which would be significant for biological applications. Cell staining, manipulation, enrichment, and detection were developed with these MNPs. Under external magnetic manipulation, the MNP-stained cells exhibited directed motions. Moreover, MNPs were printed on substrates to modulate the magnetic field distribution on the surface. Capture and detection of sparse populations of cancer cells spiked into whole blood has been explored in a microarray fashion. Cancer cells from hundreds down to only two were able to be simply and efficiently detected from 1 mL of whole blood on the MNP microarray chips. Interestingly, the cells captured through the MNP microarray still showed viability and adhered to the MNP spots after incubation, which could be utilized for cancer cell detection, localized growth, and proliferation.

    View details for DOI 10.1021/nn2034692

    View details for Web of Science ID 000300757900013

    View details for PubMedID 22229344

  • Three-dimensional imaging of single nanotube molecule endocytosis on plasmonic substrates NATURE COMMUNICATIONS Hong, G., Wu, J. Z., Robinson, J. T., Wang, H., Zhang, B., Dai, H. 2012; 3

    Abstract

    Investigating the cellular internalization pathways of single molecules or single nano objects is important to understanding cell-matter interactions, and to applications in drug delivery and discovery. Imaging and tracking the motion of single molecules on cell plasma membranes require high spatial resolution in three dimensions. Fluorescence imaging along the axial dimension with nanometre resolution has been highly challenging, but critical to revealing displacements in transmembrane events. Here, utilizing a plasmonic ruler based on the sensitive distance dependence of near-infrared fluorescence enhancement of carbon nanotubes on a gold plasmonic substrate, we probe ~10 nm scale transmembrane displacements through changes in nanotube fluorescence intensity, enabling observations of single nanotube endocytosis in three dimensions. Cellular uptake and transmembrane displacements show clear dependences to temperature and clathrin assembly on cell membrane, suggesting that the cellular entry mechanism for a nanotube molecule is via clathrin-dependent endocytosis through the formation of clathrin-coated pits on the cell membrane.

    View details for DOI 10.1038/ncomms1698

    View details for Web of Science ID 000302060100041

    View details for PubMedID 22426221

  • Spectroscopic understanding of ultra-high rate performance for LiMn0.75Fe0.25PO4 nanorods-graphene hybrid in lithium ion battery PHYSICAL CHEMISTRY CHEMICAL PHYSICS Zhou, J., Wang, J., Zuin, L., Regier, T., Hu, Y., Wang, H., Liang, Y., Maley, J., Sammynaiken, R., Dai, H. 2012; 14 (27): 9578-9581

    Abstract

    Comprehensive X-ray absorption near-edge structure spectroscopy at the C, O and Li K-edges and the Mn, Fe, and P L-edges of LiMn(0.75)Fe(0.25)PO(4) nanorods-graphene has been reported in great detail. Compared to that of free standing graphene and LiMn(0.75)Fe(0.25)PO(4), the intimate interaction between the nanorods and graphene via charge redistribution has been unambiguously confirmed. This interaction not only anchors the nanorods onto the graphene but also modifies its surface chemistry, both of which afford the nanorods-graphene hybrid an ultra-high rate performance in lithium ion batteries. Such knowledge is important for the understanding of hybrid nanomaterials for lithium ion batteries and allows rational design for further improvements in performance.

    View details for DOI 10.1039/c2cp41012e

    View details for Web of Science ID 000305581500005

    View details for PubMedID 22678419

  • In Vivo Fluorescence Imaging with Ag2S Quantum Dots in the Second Near-Infrared Region ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Hong, G., Robinson, J. T., Zhang, Y., Diao, S., Antaris, A. L., Wang, Q., Dai, H. 2012; 51 (39): 9818-9821

    Abstract

    Hits the dot: Ag(2)S quantum dots (QDs) with bright near-infrared-II fluorescence emission (around 1200 nm) and six-arm branched PEG surface coating were synthesized for in vivo small-animal imaging. The 6PEG-Ag(2)S QDs afforded a tumor uptake of approximately 10 % injected dose/gram, owing to a long circulation half-life of approximately 4 h. Clearance of the injected 6PEG-Ag(2)S QDs occurs mainly through the biliary pathway in mice.

    View details for DOI 10.1002/anie.201206059

    View details for Web of Science ID 000308886800018

    View details for PubMedID 22951900

  • Controlled Chlorine Plasma Reaction for Noninvasive Graphene Doping JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Wu, J., Xie, L., Li, Y., Wang, H., Ouyang, Y., Guo, J., Dai, H. 2011; 133 (49): 19668-19671

    Abstract

    We investigated the chlorine plasma reaction with graphene and graphene nanoribbons and compared it with the hydrogen and fluorine plasma reactions. Unlike the rapid destruction of graphene by hydrogen and fluorine plasmas, much slower reaction kinetics between the chlorine plasma and graphene were observed, allowing for controlled chlorination. Electrical measurements on graphene sheets, graphene nanoribbons, and large graphene films grown by chemical vapor deposition showed p-type doping accompanied by a conductance increase, suggesting nondestructive doping via chlorination. Ab initio simulations were performed to rationalize the differences in fluorine, hydrogen, and chlorine functionalization of graphene.

    View details for DOI 10.1021/ja2091068

    View details for Web of Science ID 000298719800027

    View details for PubMedID 22082226

  • Multifunctional FeCo-graphitic carbon nanocrystals for combined imaging, drug delivery and tumor-specific photothermal therapy in mice NANO RESEARCH Sherlock, S. P., Dai, H. 2011; 4 (12): 1248-1260
  • Co3O4 nanocrystals on graphene as a synergistic catalyst for oxygen reduction reaction NATURE MATERIALS Liang, Y., Li, Y., Wang, H., Zhou, J., Wang, J., Regier, T., Dai, H. 2011; 10 (10): 780-786

    Abstract

    Catalysts for oxygen reduction and evolution reactions are at the heart of key renewable-energy technologies including fuel cells and water splitting. Despite tremendous efforts, developing oxygen electrode catalysts with high activity at low cost remains a great challenge. Here, we report a hybrid material consisting of Co?O? nanocrystals grown on reduced graphene oxide as a high-performance bi-functional catalyst for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Although Co?O? or graphene oxide alone has little catalytic activity, their hybrid exhibits an unexpected, surprisingly high ORR activity that is further enhanced by nitrogen doping of graphene. The Co?O?/N-doped graphene hybrid exhibits similar catalytic activity but superior stability to Pt in alkaline solutions. The same hybrid is also highly active for OER, making it a high-performance non-precious metal-based bi-catalyst for both ORR and OER. The unusual catalytic activity arises from synergetic chemical coupling effects between Co?O? and graphene.

    View details for DOI 10.1038/NMAT3087

    View details for Web of Science ID 000295155200015

    View details for PubMedID 21822263

  • Graphene nanoribbons with smooth edges behave as quantum wires NATURE NANOTECHNOLOGY Wang, X., Ouyang, Y., Jiao, L., Wang, H., Xie, L., Wu, J., Guo, J., Dai, H. 2011; 6 (9): 563-567

    Abstract

    Graphene nanoribbons with perfect edges are predicted to exhibit interesting electronic and spintronic properties, notably quantum-confined bandgaps and magnetic edge states. However, so far, graphene nanoribbons produced by lithography have had rough edges, as well as low-temperature transport characteristics dominated by defects (mainly variable range hopping between localized states in a transport gap near the Dirac point). Here, we report that one- and two-layer nanoribbon quantum dots made by unzipping carbon nanotubes exhibit well-defined quantum transport phenomena, including Coulomb blockade, the Kondo effect, clear excited states up to ?20 meV, and inelastic co-tunnelling. Together with the signatures of intrinsic quantum-confined bandgaps and high conductivities, our data indicate that the nanoribbons behave as clean quantum wires at low temperatures, and are not dominated by defects.

    View details for DOI 10.1038/NNANO.2011.138

    View details for Web of Science ID 000294550000012

    View details for PubMedID 21873992

  • Plasmonic substrates for multiplexed protein microarrays with femtomolar sensitivity and broad dynamic range NATURE COMMUNICATIONS Tabakman, S. M., Lau, L., Robinson, J. T., Price, J., Sherlock, S. P., Wang, H., Zhang, B., Chen, Z., Tangsombatvisit, S., Jarrell, J. A., Utz, P. J., Dai, H. 2011; 2

    Abstract

    Protein chips are widely used for high-throughput proteomic analysis, but to date, the low sensitivity and narrow dynamic range have limited their capabilities in diagnostics and proteomics. Here we present protein microarrays on a novel nanostructured, plasmonic gold film with near-infrared fluorescence enhancement of up to 100-fold, extending the dynamic range of protein detection by three orders of magnitude towards the fM regime. We employ plasmonic protein microarrays for the early detection of a cancer biomarker, carcinoembryonic antigen, in the sera of mice bearing a xenograft tumour model. Further, we demonstrate a multiplexed autoantigen array for human autoantibodies implicated in a range of autoimmune diseases with superior signal-to-noise ratios and broader dynamic range compared with commercial nitrocellulose and glass substrates. The high sensitivity, broad dynamic range and easy adaptability of plasmonic protein chips presents new opportunities in proteomic research and diagnostics applications.

    View details for DOI 10.1038/ncomms1477

    View details for Web of Science ID 000294807200008

    View details for PubMedID 21915108

  • Advanced asymmetrical supercapacitors based on graphene hybrid materials NANO RESEARCH Wang, H., Liang, Y., Mirfakhrai, T., Chen, Z., Casalongue, H. S., Dai, H. 2011; 4 (8): 729-736
  • Spatially resolving edge states of chiral graphene nanoribbons NATURE PHYSICS Tao, C., Jiao, L., Yazyev, O. V., Chen, Y., Feng, J., Zhang, X., Capaz, R. B., Tour, J. M., Zettl, A., Louie, S. G., Dai, H., Crommie, M. F. 2011; 7 (8): 616-620

    View details for DOI 10.1038/NPHYS1991

    View details for Web of Science ID 000293354000013

  • Graphene Nanoribbons from Unzipped Carbon Nanotubes: Atomic Structures, Raman Spectroscopy, and Electrical Properties JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Xie, L., Wang, H., Jin, C., Wang, X., Jiao, L., Suenaga, K., Dai, H. 2011; 133 (27): 10394-10397

    Abstract

    We investigated the atomic structures, Raman spectroscopic and electrical transport properties of individual graphene nanoribbons (GNRs, widths ~10-30 nm) derived from sonochemical unzipping of multiwalled carbon nanotubes (MWNTs). Aberration-corrected transmission electron microscopy (TEM) revealed a high percentage of two-layer (2 L) GNRs and some single-layer ribbons. The layer-layer stacking angles ranged from 0° to 30° including average chiral angles near 30° (armchair orientation) or 0° (zigzag orientation). A large fraction of GNRs with bent and smooth edges was observed, while the rest showed flat and less smooth edges (roughness ?1 nm). Polarized Raman spectroscopy probed individual GNRs to reveal D/G ratios and ratios of D band intensities at parallel and perpendicular laser excitation polarization (D(?)/D(?)). The observed spectroscopic trends were used to infer the average chiral angles and edge smoothness of GNRs. Electrical transport and Raman measurements were carried out for individual ribbons to correlate spectroscopic and electrical properties of GNRs.

    View details for DOI 10.1021/ja203860a

    View details for Web of Science ID 000293149800019

    View details for PubMedID 21678963

  • Graphene-Wrapped Sulfur Particles as a Rechargeable Lithium-Sulfur Battery Cathode Material with High Capacity and Cycling Stability NANO LETTERS Wang, H., Yang, Y., Liang, Y., Robinson, J. T., Li, Y., Jackson, A., Cui, Y., Dai, H. 2011; 11 (7): 2644-2647

    Abstract

    We report the synthesis of a graphene-sulfur composite material by wrapping poly(ethylene glycol) (PEG) coated submicrometer sulfur particles with mildly oxidized graphene oxide sheets decorated by carbon black nanoparticles. The PEG and graphene coating layers are important to accommodating volume expansion of the coated sulfur particles during discharge, trapping soluble polysulfide intermediates, and rendering the sulfur particles electrically conducting. The resulting graphene-sulfur composite showed high and stable specific capacities up to ?600 mAh/g over more than 100 cycles, representing a promising cathode material for rechargeable lithium batteries with high energy density.

    View details for DOI 10.1021/nl200658a

    View details for Web of Science ID 000292849400013

    View details for PubMedID 21699259

  • Carbon materials for drug delivery & cancer therapy MATERIALS TODAY Liu, Z., Robinson, J. T., Tabakman, S. M., Yang, K., Dai, H. 2011; 14 (7-8): 316-323
  • Thermally Limited Current Carrying Ability of Graphene Nanoribbons PHYSICAL REVIEW LETTERS Liao, A. D., Wu, J. Z., Wang, X., Tahy, K., Jena, D., Dai, H., Pop, E. 2011; 106 (25)

    Abstract

    We investigate high-field transport in graphene nanoribbons (GNRs) on SiO(2), up to breakdown. The maximum current density is limited by self-heating, but can reach >3 mA/?m for GNRs ~15 nm wide. Comparison with larger, micron-sized graphene devices reveals that narrow GNRs benefit from 3D heat spreading into the SiO(2), which enables their higher current density. GNRs also benefit from lateral heat flow to the contacts in short devices (<~0.3 ?m), which allows extraction of a median GNR thermal conductivity (TC), ~80 W m(-1)K(-1) at 20 °C across our samples, dominated by phonons. The TC of GNRs is an order of magnitude lower than that of micron-sized graphene on SiO(2), suggesting strong roles of edge and defect scattering, and the importance of thermal dissipation in small GNR devices.

    View details for DOI 10.1103/PhysRevLett.106.256801

    View details for Web of Science ID 000291801900010

    View details for PubMedID 21770659

  • Deep-tissue anatomical imaging of mice using carbon nanotube fluorophores in the second near-infrared window PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Welsher, K., Sherlock, S. P., Dai, H. 2011; 108 (22): 8943-8948

    Abstract

    Fluorescent imaging in the second near-infrared window (NIR II, 1-1.4 ?m) holds much promise due to minimal autofluorescence and tissue scattering. Here, using well-functionalized biocompatible single-walled carbon nanotubes (SWNTs) as NIR II fluorescent imaging agents, we performed high-frame-rate video imaging of mice during intravenous injection of SWNTs and investigated the path of SWNTs through the mouse anatomy. We observed in real-time SWNT circulation through the lungs and kidneys several seconds postinjection, and spleen and liver at slightly later time points. Dynamic contrast-enhanced imaging through principal component analysis (PCA) was performed and found to greatly increase the anatomical resolution of organs as a function of time postinjection. Importantly, PCA was able to discriminate organs such as the pancreas, which could not be resolved from real-time raw images. Tissue phantom studies were performed to compare imaging in the NIR II region to the traditional NIR I biological transparency window (700-900 nm). Examination of the feature sizes of a common NIR I dye (indocyanine green) showed a more rapid loss of feature contrast and integrity with increasing feature depth as compared to SWNTs in the NIR II region. The effects of increased scattering in the NIR I versus NIR II region were confirmed by Monte Carlo simulation. In vivo fluorescence imaging in the NIR II region combined with PCA analysis may represent a powerful approach to high-resolution optical imaging through deep tissues, useful for a wide range of applications from biomedical research to disease diagnostics.

    View details for DOI 10.1073/pnas.1014501108

    View details for Web of Science ID 000291106200015

    View details for PubMedID 21576494

  • MoS2 Nanoparticles Grown on Graphene: An Advanced Catalyst for the Hydrogen Evolution Reaction JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Li, Y., Wang, H., Xie, L., Liang, Y., Hong, G., Dai, H. 2011; 133 (19): 7296-7299

    Abstract

    Advanced materials for electrocatalytic and photoelectrochemical water splitting are central to the area of renewable energy. In this work, we developed a selective solvothermal synthesis of MoS(2) nanoparticles on reduced graphene oxide (RGO) sheets suspended in solution. The resulting MoS(2)/RGO hybrid material possessed nanoscopic few-layer MoS(2) structures with an abundance of exposed edges stacked onto graphene, in strong contrast to large aggregated MoS(2) particles grown freely in solution without GO. The MoS(2)/RGO hybrid exhibited superior electrocatalytic activity in the hydrogen evolution reaction (HER) relative to other MoS(2) catalysts. A Tafel slope of ?41 mV/decade was measured for MoS(2) catalysts in the HER for the first time; this exceeds by far the activity of previous MoS(2) catalysts and results from the abundance of catalytic edge sites on the MoS(2) nanoparticles and the excellent electrical coupling to the underlying graphene network. The ?41 mV/decade Tafel slope suggested the Volmer-Heyrovsky mechanism for the MoS(2)-catalyzed HER, with electrochemical desorption of hydrogen as the rate-limiting step.

    View details for DOI 10.1021/ja201269b

    View details for Web of Science ID 000290782200016

    View details for PubMedID 21510646

  • Ultrasmall Reduced Graphene Oxide with High Near-Infrared Absorbance for Photothermal Therapy JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Robinson, J. T., Tabakman, S. M., Liang, Y., Wang, H., Casalongue, H. S., Daniel Vinh, D., Dai, H. 2011; 133 (17): 6825-6831

    Abstract

    We developed nanosized, reduced graphene oxide (nano-rGO) sheets with high near-infrared (NIR) light absorbance and biocompatibility for potential photothermal therapy. The single-layered nano-rGO sheets were ?20 nm in average lateral dimension, functionalized noncovalently by amphiphilic PEGylated polymer chains to render stability in biological solutions and exhibited 6-fold higher NIR absorption than nonreduced, covalently PEGylated nano-GO. Attaching a targeting peptide bearing the Arg-Gly-Asp (RGD) motif to nano-rGO afforded selective cellular uptake in U87MG cancer cells and highly effective photoablation of cells in vitro. In the absence of any NIR irradiation, nano-rGO exhibited little toxicity in vitro at concentrations well above the doses needed for photothermal heating. This work established nano-rGO as a novel photothermal agent due to its small size, high photothermal efficiency, and low cost as compared to other NIR photothermal agents including gold nanomaterials and carbon nanotubes.

    View details for DOI 10.1021/ja2010175

    View details for Web of Science ID 000290363400051

    View details for PubMedID 21476500

  • Hydrogen Spillover in Pt-Single-Walled Carbon Nanotube Composites: Formation of Stable C-H Bonds JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Bhowmick, R., Rajasekaran, S., Friebel, D., Beasley, C., Jiao, L., Ogasawara, H., Dai, H., Clemens, B., Nilsson, A. 2011; 133 (14): 5580-5586

    Abstract

    Using in situ electrical conductivity and ex situ X-ray photoelectron spectroscopy (XPS) measurements, we have examined how the hydrogen uptake of single-walled carbon nanotubes (SWNTs) is influenced by the addition of Pt nanoparticles. The conductivity of platinum-sputtered single-walled carbon nanotubes (Pt-SWNTs) during molecular hydrogen exposure decreased more rapidly than that of the corresponding pure SWNTs, which supports a hydrogenation mechanism facilitated by "spillover" of dissociated hydrogen from the Pt nanoparticles. C 1s XPS spectra indicate that the Pt-SWNTs store hydrogen by means of chemisorption, that is, covalent C-H bond formation: molecular hydrogen charging at elevated pressure (8.27 bar) and room temperature yielded Pt-SWNTs with up to 16 ± 1.5 at. % sp(3)-hybridized carbon atoms, which corresponds to a hydrogen-storage capacity of 1.2 wt % (excluding the weight of Pt nanoparticles). Pt-SWNTs prepared by the Langmuir-Blodgett (LB) technique exhibited the highest Pt/SWNT ratio and also the best hydrogen uptake.

    View details for DOI 10.1021/ja200403m

    View details for Web of Science ID 000289829100060

    View details for PubMedID 21428292

  • Room-Temperature Edge Functionalization and Doping of Graphene by Mild Plasma SMALL Kato, T., Jiao, L., Wang, X., Wang, H., Li, X., Zhang, L., Hatakeyama, R., Dai, H. 2011; 7 (5): 574-577

    View details for DOI 10.1002/smll.201002146

    View details for Web of Science ID 000288081900004

    View details for PubMedID 21370457

  • A New Approach to Solution-Phase Gold Seeding for SERS Substrates SMALL Tabakman, S. M., Chen, Z., Casalongue, H. S., Wang, H., Dai, H. 2011; 7 (4): 499-505

    Abstract

    Surface-enhanced Raman scattering (SERS) vastly improves signal-to-noise ratios as compared to traditional Raman scattering, making sensitive assays based upon Raman scattering a reality. However, preparation of highly stable SERS-active gold substrates requires complicated and expensive methodologies and instrumentation. Here, a general and completely solution-phase, seed-based approach is introduced, which is capable of producing gold films for SERS applications on a variety of substrates, not requiring surface modification or functionalization. SERS enhancement factors of ?10(7) were observed. Moreover, solution-phase gold film deposition on highly complex surfaces, such as protein-coated bioassays, is demonstrated for the first time. Protein bioassays coated with such SERS-active gold films are combined with bioconjugated single-walled carbon nanotube Raman labels, affording highly sensitive detection of the cancer biomarker, carcinoembryonic antigen in serum, with a limit of detection of ?5 fM (1 pg mL(-1) ).

    View details for DOI 10.1002/smll.201001836

    View details for Web of Science ID 000288080400011

    View details for PubMedID 21360809

  • Photothermally Enhanced Drug Delivery by Ultrasmall Multifunctional FeCo/Graphitic Shell Nanocrystals ACS NANO Sherlock, S. P., Tabakman, S. M., Xie, L., Dai, H. 2011; 5 (2): 1505-1512

    Abstract

    FeCo/graphitic carbon shell (FeCo/GC) nanocrystals (?4-5 nm in diameter) with ultrahigh magnetization are synthesized, functionalized, and developed into multifunctional biocompatible materials. We demonstrate the ability of this material to serve as an integrated system for combined drug delivery, near-infrared (NIR) photothermal therapy, and magnetic resonance imaging (MRI) in vitro. We show highly efficient loading of doxorubicin (DOX) by ?-stacking on the graphitic shell to afford FeCo/GC-DOX complexes and pH sensitive DOX release from the particles. We observe enhanced intracellular drug delivery by FeCo/GC-DOX under 20 min of NIR laser (808 nm) induced hyperthermia to 43 °C, resulting in a significant increase of FeCo/GC-DOX toxicity toward breast cancer cells. The synergistic cancer cell killing by FeCo/GC-DOX drug delivery under photothermal heating is due to a ?two-fold enhancement of cancer cell uptake of FeCo/GC-DOX complex and the increased DOX toxicity under the 43 °C hyperthermic condition. The combination of synergistic NIR photothermally enhanced drug delivery and MRI with the FeCo/GC nanocrystals could lead to a powerful multimodal system for biomedical detection and therapy.

    View details for DOI 10.1021/nn103415x

    View details for Web of Science ID 000287553800094

    View details for PubMedID 21284398

  • FeCo/Graphite Nanocrystals for Multi-Modality Imaging of Experimental Vascular Inflammation PLOS ONE Kosuge, H., Sherlock, S. P., Kitagawa, T., Terashima, M., Barral, J. K., Nishimura, D. G., Dai, H., McConnell, M. V. 2011; 6 (1)

    Abstract

    FeCo/graphitic-carbon nanocrystals (FeCo/GC) are biocompatible, high-relaxivity, multi-functional nanoparticles. Macrophages represent important cellular imaging targets for assessing vascular inflammation. We evaluated FeCo/GC for vascular macrophage uptake and imaging in vivo using fluorescence and MRI.Hyperlipidemic and diabetic mice underwent carotid ligation to produce a macrophage-rich vascular lesion. In situ and ex vivo fluorescence imaging were performed at 48 hours after intravenous injection of FeCo/GC conjugated to Cy5.5 (n?=?8, 8 nmol of Cy5.5/mouse). Significant fluorescence signal from FeCo/GC-Cy5.5 was present in the ligated left carotid arteries, but not in the control (non-ligated) right carotid arteries or sham-operated carotid arteries (p?=?0.03 for ligated vs. non-ligated). Serial in vivo 3T MRI was performed at 48 and 72 hours after intravenous FeCo/GC (n?=?6, 270 µg Fe/mouse). Significant T2* signal loss from FeCo/GC was seen in ligated left carotid arteries, not in non-ligated controls (p?=?0.03). Immunofluorescence staining showed colocalization of FeCo/GC and macrophages in ligated carotid arteries.FeCo/GC accumulates in vascular macrophages in vivo, allowing fluorescence and MR imaging. This multi-functional high-relaxivity nanoparticle platform provides a promising approach for cellular imaging of vascular inflammation.

    View details for DOI 10.1371/journal.pone.0014523

    View details for Web of Science ID 000286516500005

    View details for PubMedID 21264237

  • LiMn1-xFexPO4 Nanorods Grown on Graphene Sheets for Ultrahigh-Rate-Performance Lithium Ion Batteries ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Wang, H., Yang, Y., Liang, Y., Cui, L., Casalongue, H. S., Li, Y., Hong, G., Cui, Y., Dai, H. 2011; 50 (32): 7364-7368

    View details for DOI 10.1002/anie.201103163

    View details for Web of Science ID 000293840400030

    View details for PubMedID 21710671

  • Near-Infrared-Fluorescence-Enhanced Molecular Imaging of Live Cells on Gold Substrates ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Hong, G., Tabakman, S. M., Welsher, K., Chen, Z., Robinson, J. T., Wang, H., Zhang, B., Dai, H. 2011; 50 (20): 4644-4648

    View details for DOI 10.1002/anie.201100934

    View details for Web of Science ID 000290663600016

    View details for PubMedID 21506225

  • Co1-xS-Graphene Hybrid: A High-Performance Metal Chalcogenide Electrocatalyst for Oxygen Reduction ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Wang, H., Liang, Y., Li, Y., Dai, H. 2011; 50 (46): 10969-10972

    View details for DOI 10.1002/anie.201104004

    View details for Web of Science ID 000297312600042

    View details for PubMedID 21954126

  • A Dual Platform for Selective Analyte Enrichment and Ionization in Mass Spectrometry Using Aptamer-Conjugated Graphene Oxide JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Gulbakan, B., Yasun, E., Shukoor, M. I., Zhu, Z., You, M., Tan, X., Sanchez, H., Powell, D. H., Dai, H., Tan, W. 2010; 132 (49): 17408-17410

    Abstract

    This study demonstrates the use of aptamer-conjugated graphene oxide as an affinity extraction and detection platform for analytes from complex biological media. We have shown that cocaine and adenosine can be selectively enriched from plasma samples and that direct mass spectrometric readouts can be obtained without a matrix and with greatly improved signal-to-noise ratios. Aptamer-conjugated graphene oxide has clear advantages in target enrichment and in generating highly efficient ionization of target molecules for mass spectrometry. These results demonstrate the utility of the approach for analysis of small molecules in real biological samples.

    View details for DOI 10.1021/ja109042w

    View details for Web of Science ID 000285328800024

    View details for PubMedID 21090719

  • Optical Properties of Single-Walled Carbon Nanotubes Separated in a Density Gradient: Length, Bundling, and Aromatic Stacking Effects JOURNAL OF PHYSICAL CHEMISTRY C Tabakman, S. M., Welsher, K., Hong, G., Dai, H. 2010; 114 (46): 19569-19575

    Abstract

    Single-walled carbon nanotubes (SWNTs) are promising materials for in vitro and in vivo biological applications due to their high surface area and inherent near infrared photoluminescence and Raman scattering properties. Here, we use density gradient centrifugation to separate SWNTs by length and degree of bundling. Following separation, we observe a peak in photoluminescence quantum yield (PL QY) and Raman scattering intensity where SWNT length is maximized and bundling is minimized. Individualized SWNTs are found to exhibit high PL QY and high resonance-enhanced Raman scattering intensity. Fractions containing long, individual SWNTs exhibit the highest PL QY and Raman scattering intensities, compared to fractions containing single, short SWNTs or SWNT bundles. Intensity gains of approximately ~1.7 and 4-fold, respectively, are obtained compared with the starting material. Spectroscopic analysis reveals that SWNT fractions at higher displacement contain increasing proportions of SWNT bundles, which causes reduced optical transition energies and broadening of absorption features in the UV-Vis-NIR spectra, and reduced PL QY and Raman scattering intensity. Finally, we adsorb small aromatic species on "bright," individualized SWNT sidewalls and compare the resulting absorption, PL and Raman scattering effects to that of SWNT bundles. We observe similar effects in both cases, suggesting aromatic stacking affects the optical properties of SWNTs in an analogous way to SWNT bundles, likely due to electronic structure perturbations, charge transfer, and dielectric screening effects, resulting in reduction of the excitonic optical transition energies and exciton lifetimes.

    View details for DOI 10.1021/jp106453v

    View details for Web of Science ID 000284287900003

  • Metal-Enhanced Fluorescence of Carbon Nanotubes JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Hong, G., Tabakman, S. M., Welsher, K., Wang, H., Wang, X., Dai, H. 2010; 132 (45): 15920-15923

    Abstract

    The photoluminescence (PL) quantum yield of single-walled carbon nanotubes (SWNTs) is relatively low, with various quenching effects by metallic species reported in the literature. Here, we report the first case of metal enhanced fluorescence (MEF) of surfactant-coated carbon nanotubes on nanostructured gold substrates. The photoluminescence quantum yield of SWNTs is observed to be enhanced more than 10-fold. The dependence of fluorescence enhancement on metal-nanotube distance and on the surface plasmon resonance (SPR) of the gold substrate for various SWNT chiralities is measured to reveal the mechanism of enhancement. Surfactant-coated SWNTs in direct contact with metal exhibit strong MEF without quenching, suggesting a small quenching distance for SWNTs on the order of the van der Waals distance, beyond which the intrinsically fast nonradiative decay rate in nanotubes is little enhanced by metal. The metal enhanced fluorescence of SWNTs is attributed to radiative lifetime shortening through resonance coupling of SWNT emission to the reradiating dipolar plasmonic modes in the metal.

    View details for DOI 10.1021/ja1087997

    View details for Web of Science ID 000284202200029

    View details for PubMedID 20979398

  • High Performance In Vivo Near-IR (> 1 mu m) Imaging and Photothermal Cancer Therapy with Carbon Nanotubes NANO RESEARCH Robinson, J. T., Welsher, K., Tabakman, S. M., Sherlock, S. P., Wang, H., Luong, R., Dai, H. 2010; 3 (11): 779-793

    Abstract

    Short single-walled carbon nanotubes (SWNTs) functionalized by PEGylated phospholipids are biologically non-toxic and long-circulating nanomaterials with intrinsic near infrared photoluminescence (NIR PL), characteristic Raman spectra, and strong optical absorbance in the near infrared (NIR). This work demonstrates the first dual application of intravenously injected SWNTs as photoluminescent agents for in vivo tumor imaging in the 1.0-1.4 μm emission region and as NIR absorbers and heaters at 808 nm for photothermal tumor elimination at the lowest injected dose (70 μg of SWNT/mouse, equivalent to 3.6 mg/kg) and laser irradiation power (0.6 W/cm(2)) reported to date. Ex vivo resonance Raman imaging revealed the SWNT distribution within tumors at a high spatial resolution. Complete tumor elimination was achieved for large numbers of photothermally treated mice without any toxic side effects after more than six months post-treatment. Further, side-by-side experiments were carried out to compare the performance of SWNTs and gold nanorods (AuNRs) at an injected dose of 700 μg of AuNR/mouse (equivalent to 35 mg/kg) in NIR photothermal ablation of tumors in vivo. Highly effective tumor elimination with SWNTs was achieved at 10 times lower injected doses and lower irradiation powers than for AuNRs. These results suggest there are significant benefits of utilizing the intrinsic properties of biocompatible SWNTs for combined cancer imaging and therapy.

    View details for DOI 10.1007/s12274-010-0045-1

    View details for Web of Science ID 000284158700003

  • Selective Etching of Graphene Edges by Hydrogen Plasma JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Xie, L., Jiao, L., Dai, H. 2010; 132 (42): 14751-14753

    Abstract

    We devised a controlled hydrogen plasma reaction at 300 °C to etch graphene and graphene nanoribbons (GNRs) selectively at the edges over the basal plane. Atomic force microscope imaging showed that the etching rates for single-layer and few-layer (?2 layers) graphene are 0.27 ± 0.05 nm/min and 0.10 ± 0.03 nm/min, respectively. Meanwhile, Raman spectroscopic mapping revealed no D band in the planes of single-layer or few-layer graphene after the plasma reaction, suggesting selective etching at the graphene edges without introducing defects in the basal plane. We found that hydrogen plasma at lower temperature (room temperature) or a higher temperature (500 °C) could hydrogenate the basal plane or introduce defects in the basal plane. Using the hydrogen plasma reaction at the intermediate temperature (300 °C), we obtained narrow, presumably hydrogen terminated GNRs (sub-5 nm) by etching of wide GNRs derived from unzipping of multiwalled carbon nanotubes. Such GNRs exhibited semiconducting characteristics with high on/off ratios (?1000) in GNR field effect transistor devices at room temperature.

    View details for DOI 10.1021/ja107071g

    View details for Web of Science ID 000283403200021

    View details for PubMedID 20923144

  • Mn3O4-Graphene Hybrid as a High-Capacity Anode Material for Lithium Ion Batteries JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Wang, H., Cui, L., Yang, Y., Casalongue, H. S., Robinson, J. T., Liang, Y., Cui, Y., Dai, H. 2010; 132 (40): 13978-13980

    Abstract

    We developed two-step solution-phase reactions to form hybrid materials of Mn(3)O(4) nanoparticles on reduced graphene oxide (RGO) sheets for lithium ion battery applications. Selective growth of Mn(3)O(4) nanoparticles on RGO sheets, in contrast to free particle growth in solution, allowed for the electrically insulating Mn(3)O(4) nanoparticles to be wired up to a current collector through the underlying conducting graphene network. The Mn(3)O(4) nanoparticles formed on RGO show a high specific capacity up to ?900 mAh/g, near their theoretical capacity, with good rate capability and cycling stability, owing to the intimate interactions between the graphene substrates and the Mn(3)O(4) nanoparticles grown atop. The Mn(3)O(4)/RGO hybrid could be a promising candidate material for a high-capacity, low-cost, and environmentally friendly anode for lithium ion batteries. Our growth-on-graphene approach should offer a new technique for the design and synthesis of battery electrodes based on highly insulating materials.

    View details for DOI 10.1021/ja105296a

    View details for Web of Science ID 000282660100010

    View details for PubMedID 20853844

  • TiO2 Nanocrystals Grown on Graphene as Advanced Photocatalytic Hybrid Materials NANO RESEARCH Liang, Y., Wang, H., Casalongue, H. S., Chen, Z., Dai, H. 2010; 3 (10): 701-705
  • Etching and narrowing of graphene from the edges NATURE CHEMISTRY Wang, X., Dai, H. 2010; 2 (8): 661-665

    Abstract

    Large-scale graphene electronics requires lithographic patterning of narrow graphene nanoribbons for device integration. However, conventional lithography can only reliably pattern approximately 20-nm-wide GNR arrays limited by lithography resolution, while sub-5-nm GNRs are desirable for high on/off ratio field-effect transistors at room temperature. Here, we devised a gas phase chemical approach to etch graphene from the edges without damaging its basal plane. The reaction involved high temperature oxidation of graphene in a slightly reducing environment in the presence of ammonia to afford controlled etch rate (less than or approximately 1 nm min(-1)). We fabricated approximately 20-30-nm-wide graphene nanoribbon arrays lithographically, and used the gas phase etching chemistry to narrow the ribbons down to <10 nm. For the first time, a high on/off ratio up to approximately 10(4) was achieved at room temperature for field-effect transistors built with sub-5-nm-wide graphene nanoribbon semiconductors derived from lithographic patterning and narrowing. Our controlled etching method opens up a chemical way to control the size of various graphene nano-structures beyond the capability of top-down lithography.

    View details for DOI 10.1038/NCHEM.719

    View details for Web of Science ID 000280199500017

    View details for PubMedID 20651729

  • Edge magnetotransport fingerprints in disordered graphene nanoribbons PHYSICAL REVIEW B Poumirol, J., Cresti, A., Roche, S., Escoffier, W., Goiran, M., Wang, X., Li, X., Dai, H., Raquet, B. 2010; 82 (4)
  • Ni(OH)(2) Nanoplates Grown on Graphene as Advanced Electrochemical Pseudocapacitor Materials JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Wang, H., Casalongue, H. S., Liang, Y., Dai, H. 2010; 132 (21): 7472-7477

    Abstract

    Ni(OH)(2) nanocrystals grown on graphene sheets with various degrees of oxidation are investigated as electrochemical pseudocapacitor materials for potential energy storage applications. Single-crystalline Ni(OH)(2) hexagonal nanoplates directly grown on lightly oxidized, electrically conducting graphene sheets (GS) exhibit a high specific capacitance of approximately 1335 F/g at a charge and discharge current density of 2.8 A/g and approximately 953 F/g at 45.7 A/g with excellent cycling ability. The high specific capacitance and remarkable rate capability are promising for applications in supercapacitors with both high energy and power densities. A simple physical mixture of pre-synthesized Ni(OH)(2) nanoplates and graphene sheets shows lower specific capacitance, highlighting the importance of direct growth of nanomaterials on graphene to impart intimate interactions and efficient charge transport between the active nanomaterials and the conducting graphene network. Single-crystalline Ni(OH)(2) nanoplates directly grown on graphene sheets also significantly outperform small Ni(OH)(2) nanoparticles grown on heavily oxidized, electrically insulating graphite oxide (GO), suggesting that the electrochemical performance of these composites is dependent on the quality of graphene substrates and the morphology and crystallinity of the nanomaterials grown on top. These results suggest the importance of rational design and synthesis of graphene-based nanocomposite materials for high-performance energy applications.

    View details for DOI 10.1021/ja102267j

    View details for Web of Science ID 000278190600049

    View details for PubMedID 20443559

  • Aligned graphene nanoribbons and crossbars from unzipped carbon nanotubes NANO RESEARCH Jiao, L., Zhang, L., Ding, L., Liu, J., Dai, H. 2010; 3 (6): 387-394
  • Ultrahigh Sensitivity Carbon Nanotube Agents for Photoacoustic Molecular Imaging in Living Mice NANO LETTERS de la Zerda, A., Liu, Z., Bodapati, S., Teed, R., Vaithilingam, S., Khuri-Yakub, B. T., Chen, X., Dai, H., Gambhir, S. S. 2010; 10 (6): 2168-2172

    Abstract

    Photoacoustic imaging is an emerging modality that overcomes to a great extent the resolution and depth limitations of optical imaging while maintaining relatively high-contrast. However, since many diseases will not manifest an endogenous photoacoustic contrast, it is essential to develop exogenous photoacoustic contrast agents that can target diseased tissue(s). Here we present a novel photoacoustic contrast agent, Indocyanine Green dye-enhanced single walled carbon nanotube (SWNT-ICG). We conjugated this contrast agent with cyclic Arg-Gly-Asp (RGD) peptides to molecularly target the alpha(v)beta(3) integrins, which are associated with tumor angiogenesis. Intravenous administration of this tumor-targeted contrast agent to tumor-bearing mice showed significantly higher photoacoustic signal in the tumor than in mice injected with the untargeted contrast agent. The new contrast agent gave a markedly 300 times higher photoacoustic contrast in living tissues than previously reported SWNTs, leading to subnanomolar sensitivities. Finally, we show that the new contrast agent can detect approximately 20 times fewer cancer cells than previously reported SWNTs.

    View details for DOI 10.1021/nl100890d

    View details for Web of Science ID 000278449200033

    View details for PubMedID 20499887

  • Facile synthesis of high-quality graphene nanoribbons NATURE NANOTECHNOLOGY Jiao, L., Wang, X., Diankov, G., Wang, H., Dai, H. 2010; 5 (5): 321-325

    Abstract

    Graphene nanoribbons have attracted attention because of their novel electronic and spin transport properties, and also because nanoribbons less than 10 nm wide have a bandgap that can be used to make field-effect transistors. However, producing nanoribbons of very high quality, or in high volumes, remains a challenge. Here, we show that pristine few-layer nanoribbons can be produced by unzipping mildly gas-phase oxidized multiwalled carbon nanotubes using mechanical sonication in an organic solvent. The nanoribbons are of very high quality, with smooth edges (as seen by high-resolution transmission electron microscopy), low ratios of disorder to graphitic Raman bands, and the highest electrical conductance and mobility reported so far (up to 5e(2)/h and 1,500 cm(2) V(-1) s(-1) for ribbons 10-20 nm in width). Furthermore, at low temperatures, the nanoribbons show phase-coherent transport and Fabry-Perot interference, suggesting minimal defects and edge roughness. The yield of nanoribbons is approximately 2% of the starting raw nanotube soot material, significantly higher than previous methods capable of producing high-quality narrow nanoribbons. The relatively high-yield synthesis of pristine graphene nanoribbons will make these materials easily accessible for a wide range of fundamental and practical applications.

    View details for DOI 10.1038/NNANO.2010.54

    View details for Web of Science ID 000278264300008

    View details for PubMedID 20364133

  • Nanocrystal Growth on Graphene with Various Degrees of Oxidation JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Wang, H., Robinson, J. T., Diankov, G., Dai, H. 2010; 132 (10): 3270-?

    Abstract

    We show a general two-step method for growing hydroxide and oxide nanocrystals of the iron family elements (Ni, Co, Fe) on graphene with two degrees of oxidation. Drastically different nanocrystal growth behaviors were observed on low-oxidation graphene sheets (GS) and highly oxidized graphite oxide (GO) in hydrothermal reactions. Small particles precoated on GS with few oxygen-containing surface groups diffused and recrystallized into single-crystalline Ni(OH)(2) hexagonal nanoplates or Fe(2)O(3) nanorods with well-defined morphologies. In contrast, particles precoated on GO were pinned by the high-concentration oxygen groups and defects on GO without recrystallization into well-defined shapes. Adjusting the reaction temperature can be included to further control materials grown on graphene. For materials with weak interactions with graphene, increasing the reaction temperature can lead to diffusion and recrystallization of surface species into larger crystals, even on highly oxidized and defective GO. Our results suggest an interesting new approach for controlling the morphology of nanomaterials grown on graphene by tuning the surface chemistry of graphene substrates used for crystal nucleation and growth.

    View details for DOI 10.1021/ja100329d

    View details for Web of Science ID 000275660600020

    View details for PubMedID 20166667

  • Multiplexed Five-Color Molecular Imaging of Cancer Cells and Tumor Tissues with Carbon Nanotube Raman Tags in the Near-Infrared NANO RESEARCH Liu, Z., Tabakman, S., Sherlock, S., Li, X., Chen, Z., Jiang, K., Fan, S., Dai, H. 2010; 3 (3): 222-233
  • Projected Performance Advantage of Multilayer Graphene Nanoribbons as a Transistor Channel Material NANO RESEARCH Ouyang, Y., Dai, H., Guo, J. 2010; 3 (1): 8-15
  • High-Contrast In Vivo Visualization of Microvessels Using Novel FeCo/GC Magnetic Nanocrystals MAGNETIC RESONANCE IN MEDICINE Lee, J. H., Sherlock, S. P., Terashima, M., Kosuge, H., Suzuki, Y., Goodwin, A., Robinson, J., Seo, W. S., Liu, Z., Luong, R., McConnell, M. V., Nishimura, D. G., Dai, H. 2009; 62 (6): 1497-1509

    Abstract

    FeCo-graphitic carbon shell nanocrystals are a novel MRI contrast agent with unprecedented high per-metal-atom-basis relaxivity (r(1) = 97 mM(-1) sec(-1), r(2) = 400 mM(-1) sec(-1)) and multifunctional capabilities. While the conventional gadolinium-based contrast-enhanced angiographic magnetic MRI has proven useful for diagnosis of vascular diseases, its short circulation time and relatively low sensitivity render high-resolution MRI of morphologically small vascular structures such as those involved in collateral, arteriogenic, and angiogenic vessel formation challenging. Here, by combining FeCo-graphitic carbon shell nanocrystals with high-resolution MRI technique, we demonstrate that such microvessels down to approximately 100 mum can be monitored in high contrast and noninvasively using a conventional 1.5-T clinical MRI system, achieving a diagnostic imaging standard approximating that of the more invasive X-ray angiography. Preliminary in vitro and in vivo toxicity study results also show no sign of toxicity.

    View details for DOI 10.1002/mrm.22132

    View details for Web of Science ID 000272067600017

    View details for PubMedID 19859938

  • Simultaneous Nitrogen Doping and Reduction of Graphene Oxide JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Li, X., Wang, H., Robinson, J. T., Sanchez, H., Diankov, G., Dai, H. 2009; 131 (43): 15939-15944

    Abstract

    We developed a simple chemical method to obtain bulk quantities of N-doped, reduced graphene oxide (GO) sheets through thermal annealing of GO in ammonia. X-ray photoelectron spectroscopy (XPS) study of GO sheets annealed at various reaction temperatures reveals that N-doping occurs at a temperature as low as 300 degrees C, while the highest doping level of approximately 5% N is achieved at 500 degrees C. N-doping is accompanied by the reduction of GO with decreases in oxygen levels from approximately 28% in as-made GO down to approximately 2% in 1100 degrees C NH(3) reacted GO. XPS analysis of the N binding configurations of doped GO finds pyridinic N in the doped samples, with increased quaternary N (N that replaced the carbon atoms in the graphene plane) in GO annealed at higher temperatures (> or = 900 degrees C). Oxygen groups in GO were found responsible for reactions with NH(3) and C-N bond formation. Prereduced GO with fewer oxygen groups by thermal annealing in H(2) exhibits greatly reduced reactivity with NH(3) and a lower N-doping level. Electrical measurements of individual GO sheet devices demonstrate that GO annealed in NH(3) exhibits higher conductivity than those annealed in H(2), suggesting more effective reduction of GO by annealing in NH(3) than in H(2), consistent with XPS data. The N-doped reduced GO shows clearly n-type electron doping behavior with the Dirac point (DP) at negative gate voltages in three terminal devices. Our method could lead to the synthesis of bulk amounts of N-doped, reduced GO sheets useful for various practical applications.

    View details for DOI 10.1021/ja907098f

    View details for Web of Science ID 000271513600067

    View details for PubMedID 19817436

  • A route to brightly fluorescent carbon nanotubes for near-infrared imaging in mice NATURE NANOTECHNOLOGY Welsher, K., Liu, Z., Sherlock, S. P., Robinson, J. T., Chen, Z., Daranciang, D., Dai, H. 2009; 4 (11): 773-780

    Abstract

    The near-infrared photoluminescence intrinsic to semiconducting single-walled carbon nanotubes is ideal for biological imaging owing to the low autofluorescence and deep tissue penetration in the near-infrared region beyond 1 microm. However, biocompatible single-walled carbon nanotubes with high quantum yield have been elusive. Here, we show that sonicating single-walled carbon nanotubes with sodium cholate, followed by surfactant exchange to form phospholipid-polyethylene glycol coated nanotubes, produces in vivo imaging agents that are both bright and biocompatible. The exchange procedure is better than directly sonicating the tubes with the phospholipid-polyethylene glycol, because it results in less damage to the nanotubes and improves the quantum yield. We show whole-animal in vivo imaging using an InGaAs camera in the 1-1.7 microm spectral range by detecting the intrinsic near-infrared photoluminescence of the 'exchange' single-walled carbon nanotubes at a low dose (17 mg l(-1) injected dose). The deep tissue penetration and low autofluorescence background allowed high-resolution intravital microscopy imaging of tumour vessels beneath thick skin.

    View details for DOI 10.1038/NNANO.2009.294

    View details for Web of Science ID 000272413500022

    View details for PubMedID 19893526

  • Hierarchy of Electronic Properties of Chemically Derived and Pristine Graphene Probed by Microwave Imaging NANO LETTERS Kundhikanjana, W., Lai, K., Wang, H., Dai, H., Kelly, M. A., Shen, Z. 2009; 9 (11): 3762-3765

    Abstract

    Local electrical imaging using microwave impedance microscope is performed on graphene in different modalities, yielding a rich hierarchy of the local conductivity. The low-conductivity graphite oxide and its derivatives show significant electronic inhomogeneity. For the conductive chemical graphene, the residual defects lead to a systematic reduction of the microwave signals. In contrast, the signals on pristine graphene agree well with a lumped-element circuit model. The local impedance information can also be used to verify the electrical contact between overlapped graphene pieces.

    View details for DOI 10.1021/nl901949z

    View details for Web of Science ID 000271566400017

    View details for PubMedID 19678669

  • Solvothermal Reduction of Chemically Exfoliated Graphene Sheets JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Wang, H., Robinson, J. T., Li, X., Dai, H. 2009; 131 (29): 9910-?

    Abstract

    We have developed a solvothermal reduction method that affords more effective reduction of chemically derived graphene sheets and graphite oxide than low-temperature reduction methods. Solvothermal reduction removed oxygen and defects from graphene sheets, increased the size of sp(2) domains, and produced materials that were as conducting as pristine graphene and exhibited clear intrinsic Dirac behavior.

    View details for DOI 10.1021/ja904251p

    View details for Web of Science ID 000268395000026

    View details for PubMedID 19580268

  • N-Doping of Graphene Through Electrothermal Reactions with Ammonia SCIENCE Wang, X., Li, X., Zhang, L., Yoon, Y., Weber, P. K., Wang, H., Guo, J., Dai, H. 2009; 324 (5928): 768-771

    Abstract

    Graphene is readily p-doped by adsorbates, but for device applications, it would be useful to access the n-doped material. Individual graphene nanoribbons were covalently functionalized by nitrogen species through high-power electrical joule heating in ammonia gas, leading to n-type electronic doping consistent with theory. The formation of the carbon-nitrogen bond should occur mostly at the edges of graphene where chemical reactivity is high. X-ray photoelectron spectroscopy and nanometer-scale secondary ion mass spectroscopy confirm the carbon-nitrogen species in graphene thermally annealed in ammonia. We fabricated an n-type graphene field-effect transistor that operates at room temperature.

    View details for DOI 10.1126/science.1170335

    View details for Web of Science ID 000265832400041

    View details for PubMedID 19423822

  • Narrow graphene nanoribbons from carbon nanotubes NATURE Jiao, L., Zhang, L., Wang, X., Diankov, G., Dai, H. 2009; 458 (7240): 877-880

    Abstract

    Graphene nanoribbons (GNRs) are materials with properties distinct from those of other carbon allotropes. The all-semiconducting nature of sub-10-nm GNRs could bypass the problem of the extreme chirality dependence of the metal or semiconductor nature of carbon nanotubes (CNTs) in future electronics. Currently, making GNRs using lithographic, chemical or sonochemical methods is challenging. It is difficult to obtain GNRs with smooth edges and controllable widths at high yields. Here we show an approach to making GNRs by unzipping multiwalled carbon nanotubes by plasma etching of nanotubes partly embedded in a polymer film. The GNRs have smooth edges and a narrow width distribution (10-20 nm). Raman spectroscopy and electrical transport measurements reveal the high quality of the GNRs. Unzipping CNTs with well-defined structures in an array will allow the production of GNRs with controlled widths, edge structures, placement and alignment in a scalable fashion for device integration.

    View details for DOI 10.1038/nature07919

    View details for Web of Science ID 000265182500040

    View details for PubMedID 19370031

  • PEG Branched Polymer for Functionalization of Nanomaterials with Ultralong Blood Circulation JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Prencipe, G., Tabakman, S. M., Welsher, K., Liu, Z., Goodwin, A. P., Zhang, L., Henry, J., Dai, H. 2009; 131 (13): 4783-4787

    Abstract

    Nanomaterials have been actively pursued for biological and medical applications in recent years. Here, we report the synthesis of several new poly(ethylene glycol) grafted branched polymers for functionalization of various nanomaterials including carbon nanotubes, gold nanoparticles (NPs), and gold nanorods (NRs), affording high aqueous solubility and stability for these materials. We synthesize different surfactant polymers based upon poly(gamma-glutamic acid) (gammaPGA) and poly(maleic anhydride-alt-1-octadecene) (PMHC18). We use the abundant free carboxylic acid groups of gammaPGA for attaching lipophilic species such as pyrene or phospholipid, which bind to nanomaterials via robust physisorption. Additionally, the remaining carboxylic acids on gammaPGA or the amine-reactive anhydrides of PMHC18 are then PEGylated, providing extended hydrophilic groups, affording polymeric amphiphiles. We show that single-walled carbon nanotubes (SWNTs), Au NPs, and NRs functionalized by the polymers exhibit high stability in aqueous solutions at different pH values, at elevated temperatures, and in serum. Moreover, the polymer-coated SWNTs exhibit remarkably long blood circulation (t(1/2) = 22.1 h) upon intravenous injection into mice, far exceeding the previous record of 5.4 h. The ultralong blood circulation time suggests greatly delayed clearance of nanomaterials by the reticuloendothelial system (RES) of mice, a highly desired property for in vivo applications of nanomaterials, including imaging and drug delivery.

    View details for DOI 10.1021/ja809086q

    View details for Web of Science ID 000264806300052

    View details for PubMedID 19173646

  • Chemical Self-Assembly of Graphene Sheets NANO RESEARCH Wang, H., Wang, X., Li, X., Dai, H. 2009; 2 (4): 336-342
  • Optical Characterizations and Electronic Devices of Nearly Pure (10,5) Single-Walled Carbon Nanotubes JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Zhang, L., Tu, X., Welsher, K., Wang, X., Zheng, M., Dai, H. 2009; 131 (7): 2454-?

    Abstract

    It remains an elusive goal to achieve high-performance single-walled carbon nanotube (SWNT) field-effect transistors (FETs) composed of only single-chirality SWNTs. Many separation mechanisms have been devised and various degrees of separation demonstrated, yet it is still difficult to reach the goal of total fractionation of a given nanotube mixture into its single-chirality components. Chromatography has been reported to separate small SWNTs (diameter < or = 0.9 nm) according to their diameter, chirality, and length. The separation efficiency decreased with increasing tube diameter when the ssDNA sequence d(GT)(n) (n = 10-45) was used. Here we report our results on the separation of single-chirality (10,5) SWNTs (diameter = 1.03 nm) from HiPco tubes using ion-exchange chromatography. The separation efficiency was improved by using the new DNA sequence (TTTA)(3)T, which can recognize SWNTs with the specific chirality (10,5). The chirality of the separated tubes was examined by optical absorption, Raman, photoluminescence excitation/emission, and electrical transport measurements. All of the spectroscopic methods gave a single peak of (10,5) tubes. The purity was 99% according to the electrical measurement. The FETs composed of separated SWNTs in parallel gave an I(on)/I(off) ratio up to 10(6) due to the single-chirality-enriched (10,5) tubes. This is the first time that SWNT FETs with single-chirality SWNTs have been achieved. The chromatography method has the potential to separate even larger diameter semiconducting SWNTs from other starting materials to further improve the performance of the SWNT FETs.

    View details for DOI 10.1021/ja8096674

    View details for Web of Science ID 000263576100018

    View details for PubMedID 19193007

  • Carbon Nanotubes in Biology and Medicine: In vitro and in vivo Detection, Imaging and Drug Delivery NANO RESEARCH Liu, Z., Tabakman, S., Welsher, K., Dai, H. 2009; 2 (2): 85-120

    Abstract

    Carbon nanotubes exhibit many unique intrinsic physical and chemical properties and have been intensively explored for biological and biomedical applications in the past few years. In this comprehensive review, we summarize the main results from our and other groups in this field and clarify that surface functionalization is critical to the behavior of carbon nanotubes in biological systems. Ultrasensitive detection of biological species with carbon nanotubes can be realized after surface passivation to inhibit the non-specific binding of biomolecules on the hydrophobic nanotube surface. Electrical nanosensors based on nanotubes provide a label-free approach to biological detection. Surface-enhanced Raman spectroscopy of carbon nanotubes opens up a method of protein microarray with detection sensitivity down to 1 fmol/L. In vitro and in vivo toxicity studies reveal that highly water soluble and serum stable nanotubes are biocompatible, nontoxic, and potentially useful for biomedical applications. In vivo biodistributions vary with the functionalization and possibly also size of nanotubes, with a tendency to accumulate in the reticuloendothelial system (RES), including the liver and spleen, after intravenous administration. If well functionalized, nanotubes may be excreted mainly through the biliary pathway in feces. Carbon nanotube-based drug delivery has shown promise in various In vitro and in vivo experiments including delivery of small interfering RNA (siRNA), paclitaxel and doxorubicin. Moreover, single-walled carbon nanotubes with various interesting intrinsic optical properties have been used as novel photoluminescence, Raman, and photoacoustic contrast agents for imaging of cells and animals. Further multidisciplinary explorations in this field may bring new opportunities in the realm of biomedicine.

    View details for DOI 10.1007/s12274-009-9009-8

    View details for Web of Science ID 000273939000001

  • Phospholipid-Dextran with a Single Coupling Point: A Useful Amphiphile for Functionalization of Nanomaterials JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Goodwin, A. P., Tabakman, S. M., Welsher, K., Sherlock, S. P., Prencipe, G., Dai, H. 2009; 131 (1): 289-296

    Abstract

    Nanomaterials hold much promise for biological applications, but they require appropriate functionalization to provide biocompatibility in biological environments. For noncovalent functionalization with biocompatible polymers, the polymer must also remain attached to the nanomaterial after removal of its excess to mimic the high-dilution conditions of administration in vivo. Reported here are the synthesis and utilization of singly substituted conjugates of dextran and a phospholipid (dextran-DSPE) as stable coatings for nanomaterials. Suspensions of single-walled carbon nanotubes were found not only to be stable to phosphate buffered saline (PBS), serum, and a variety of pH's after excess polymer removal, but also to provide brighter photoluminescence than carbon nanotubes suspended by poly(ethylene glycol)-DSPE. In addition, both gold nanoparticles (AuNPs) and gold nanorods (AuNRs) were found to maintain their dispersion and characteristic optical absorbance after transfer into dextran-DSPE and were obtained in much better yield than similar suspensions with PEG-phospholipid and commonly used thiol-PEG. These suspensions were also stable to PBS, serum, and a variety of pH's after removal of excess polymer. dextran-DSPE thus shows great promise as a general surfactant material for the functionalization of a variety of nanomaterials, which could facilitate future biological applications.

    View details for DOI 10.1021/ja807307e

    View details for Web of Science ID 000262483100060

    View details for PubMedID 19061329

  • Preparation of carbon nanotube bioconjugates for biomedical applications NATURE PROTOCOLS Liu, Z., Tabakman, S. M., Chen, Z., Dai, H. 2009; 4 (9): 1372-1382

    Abstract

    Biomedical applications of carbon nanotubes have attracted much attention in recent years. Here, we summarize our previously developed protocols for functionalization and bioconjugation of single-walled carbon nanotubes (SWNTs) for various biomedical applications including biological imaging; using nanotubes as Raman, photoluminescence and photoacoustic labels; sensing using nanotubes as Raman tags and drug delivery. Sonication of SWNTs in solutions of phospholipid-polyethylene glycol (PL-PEG) is our most commonly used protocol of SWNT functionalization. Compared with other frequently used covalent strategies, our non-covalent functionalization protocol largely retains the intrinsic optical properties of SWNTs, which are useful in various biological imaging and sensing applications. Functionalized SWNTs are conjugated with targeting ligands, including peptides and antibodies for specific cell labeling in vitro or tumor targeting in vivo. Radio labels are introduced for tracking and imaging of SWNTs in real time in vivo. Moreover, SWNTs can be conjugated with small interfering RNA (siRNA) or loaded with chemotherapy drugs for drug delivery. These procedures take various times ranging from 1 to 5 d.

    View details for DOI 10.1038/nprot.2009.146

    View details for Web of Science ID 000270601700014

    View details for PubMedID 19730421

  • Supramolecular Stacking of Doxorubicin on Carbon Nanotubes for In Vivo Cancer Therapy ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Liu, Z., Fan, A. C., Rakhra, K., Sherlock, S., Goodwin, A., Chen, X., Yang, Q., Felsher, D. W., Dai, H. 2009; 48 (41): 7668-7672

    View details for DOI 10.1002/anie.200902612

    View details for Web of Science ID 000270436900037

    View details for PubMedID 19760685

  • Separation of Nanoparticles in a Density Gradient: FeCo@C and Gold Nanocrystals ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Sun, X., Tabakman, S. M., Seo, W., Zhang, L., Zhang, G., Sherlock, S., Bai, L., Dai, H. 2009; 48 (5): 939-942

    View details for DOI 10.1002/anie.200805047

    View details for Web of Science ID 000263082200016

    View details for PubMedID 19107884

  • Photoacoustic Molecular Imaging using Single Walled Carbon Nanotubes in Living Mice PHOTONS PLUS ULTRASOUND: IMAGING AND SENSING 2009 de la Zerda, A., Zavaleta, C., Keren, S., Vaithilingam, S., Bodapati, S., Teed, R., Liu, Z., Levi, J., Smith, B. R., Ma, T., Oralkan, O., Cheng, Z., Chen, X., Dai, H., Khuri-Yakub, B. T., Gambhir, S. S. 2009; 7177

    View details for DOI 10.1117/12.806497

    View details for Web of Science ID 000285714100066

  • Enhanced Sensitivity Carbon Nanotubes as Targeted Photoacoustic Molecular Imaging Agents PHOTONS PLUS ULTRASOUND: IMAGING AND SENSING 2009 de la Zerda, A., Liu, Z., Zavaleta, C., Bodapati, S., Teed, R., Vaithilingam, S., Ma, T., Oralkan, O., Chen, X., Khuri-Yakub, B. T., Dai, H., Gambhir, S. S. 2009; 7177

    View details for DOI 10.1117/12.809601

    View details for Web of Science ID 000285714100080

  • Synthesis of Ultrasmall Ferromagnetic Face-Centered Tetragonal FePt-Graphite Core-Shell Nanocrystals SMALL Seo, W. S., Kim, S. M., Kim, Y., Sun, X., Dai, H. 2008; 4 (11): 1968-1971

    View details for DOI 10.1002/smll.200800257

    View details for Web of Science ID 000261230400018

    View details for PubMedID 18752210

  • Protein microarrays with carbon nanotubes as multicolor Raman labels NATURE BIOTECHNOLOGY Chen, Z., Tabakman, S. M., Goodwin, A. P., Kattah, M. G., Daranciang, D., Wang, X., Zhang, G., Li, X., Liu, Z., Utz, P. J., Jiang, K., Fan, S., Dai, H. 2008; 26 (11): 1285-1292

    Abstract

    The current sensitivity of standard fluorescence-based protein detection limits the use of protein arrays in research and clinical diagnosis. Here, we use functionalized, macromolecular single-walled carbon nanotubes (SWNTs) as multicolor Raman labels for highly sensitive, multiplexed protein detection in an arrayed format. Unlike fluorescence methods, Raman detection benefits from the sharp scattering peaks of SWNTs with minimal background interference, affording a high signal-to-noise ratio needed for ultra-sensitive detection. When combined with surface-enhanced Raman scattering substrates, the strong Raman intensity of SWNT tags affords protein detection sensitivity in sandwich assays down to 1 fM--a three-order-of-magnitude improvement over most reports of fluorescence-based detection. We use SWNT Raman tags to detect human autoantibodies against proteinase 3, a biomarker for the autoimmune disease Wegener's granulomatosis, diluted up to 10(7)-fold in 1% human serum. SWNT Raman tags are not subject to photobleaching or quenching. By conjugating different antibodies to pure (12)C and (13)C SWNT isotopes, we demonstrate multiplexed two-color SWNT Raman-based protein detection.

    View details for DOI 10.1038/nbt.1501

    View details for Web of Science ID 000260832200024

    View details for PubMedID 18953353

  • Multiplexed multicolor Raman imaging of live cells with isotopically modified single walled carbon nanotubes JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Liu, Z., Li, X., Tabakman, S. M., Jiang, K., Fan, S., Dai, H. 2008; 130 (41): 13540-?

    Abstract

    We show that single walled carbon nanotubes (SWNTs) with different isotope compositions exhibit distinct Raman G-band peaks and can be used for multiplexed multicolor Raman imaging of biological systems. Cancer cells with specific receptors are selectively labeled with three differently "colored" SWNTs conjugated with various targeting ligands including Herceptin (anti-Her2), Erbitux (anti-Her1), and RGD peptide, allowing for multicolor Raman imaging of cells in a multiplexed manner. SWNT Raman signals are highly robust against photobleaching, allowing long-term imaging and tracking. With narrow peak features, SWNT Raman signals are easily differentiated from the autofluorescence background. The SWNT Raman excitation and scattering photons are in the near-infrared region, which is the most transparent optical window for biological systems in vitro and in vivo. Thus, SWNTs are novel Raman tags promising for multiplexed biological detection and imaging.

    View details for DOI 10.1021/ja806242t

    View details for Web of Science ID 000259924000017

    View details for PubMedID 18803379

  • Converting Metallic Single-Walled Carbon Nanotnbes into Semiconductors by Boron/Nitrogen Co-Doping ADVANCED MATERIALS Xu, Z., Lu, W., Wang, W., Gu, C., Liu, K., Bai, X., Wang, E., Dai, H. 2008; 20 (19): 3615-?
  • Carbon nanotubes as photoacoustic molecular imaging agents in living mice NATURE NANOTECHNOLOGY de la Zerda, A., Zavaleta, C., Keren, S., Vaithilingam, S., Bodapati, S., Liu, Z., Levi, J., Smith, B. R., Ma, T., Oralkan, O., Cheng, Z., Chen, X., Dai, H., Khuri-Yakub, B. T., Gambhir, S. S. 2008; 3 (9): 557-562

    Abstract

    Photoacoustic imaging of living subjects offers higher spatial resolution and allows deeper tissues to be imaged compared with most optical imaging techniques. As many diseases do not exhibit a natural photoacoustic contrast, especially in their early stages, it is necessary to administer a photoacoustic contrast agent. A number of contrast agents for photoacoustic imaging have been suggested previously, but most were not shown to target a diseased site in living subjects. Here we show that single-walled carbon nanotubes conjugated with cyclic Arg-Gly-Asp (RGD) peptides can be used as a contrast agent for photoacoustic imaging of tumours. Intravenous administration of these targeted nanotubes to mice bearing tumours showed eight times greater photoacoustic signal in the tumour than mice injected with non-targeted nanotubes. These results were verified ex vivo using Raman microscopy. Photoacoustic imaging of targeted single-walled carbon nanotubes may contribute to non-invasive cancer imaging and monitoring of nanotherapeutics in living subjects.

    View details for DOI 10.1038/nnano.2008.231

    View details for Web of Science ID 000259013100014

    View details for PubMedID 18772918

  • Nano-Graphene Oxide for Cellular Imaging and Drug Delivery NANO RESEARCH Sun, X., Liu, Z., Welsher, K., Robinson, J. T., Goodwin, A., Zaric, S., Dai, H. 2008; 1 (3): 203-212

    Abstract

    Two-dimensional graphene offers interesting electronic, thermal, and mechanical properties that are currently being explored for advanced electronics, membranes, and composites. Here we synthesize and explore the biological applications of nano-graphene oxide (NGO), i.e., single-layer graphene oxide sheets down to a few nanometers in lateral width. We develop functionalization chemistry in order to impart solubility and compatibility of NGO in biological environments. We obtain size separated pegylated NGO sheets that are soluble in buffers and serum without agglomeration. The NGO sheets are found to be photoluminescent in the visible and infrared regions. The intrinsic photoluminescence (PL) of NGO is used for live cell imaging in the near-infrared (NIR) with little background. We found that simple physisorption via pi-stacking can be used for loading doxorubicin, a widely used cancer drug onto NGO functionalized with antibody for selective killing of cancer cells in vitro. Owing to its small size, intrinsic optical properties, large specific surface area, low cost, and useful non-covalent interactions with aromatic drug molecules, NGO is a promising new material for biological and medical applications.

    View details for DOI 10.1007/s12274-008-8021-8

    View details for Web of Science ID 000207467200003

  • Highly conducting graphene sheets and Langmuir-Blodgett films NATURE NANOTECHNOLOGY Li, X., Zhang, G., Bai, X., Sun, X., Wang, X., Wang, E., Dai, H. 2008; 3 (9): 538-542

    Abstract

    Graphene is an intriguing material with properties that are distinct from those of other graphitic systems. The first samples of pristine graphene were obtained by 'peeling off' and epitaxial growth. Recently, the chemical reduction of graphite oxide was used to produce covalently functionalized single-layer graphene oxide. However, chemical approaches for the large-scale production of highly conducting graphene sheets remain elusive. Here, we report that the exfoliation-reintercalation-expansion of graphite can produce high-quality single-layer graphene sheets stably suspended in organic solvents. The graphene sheets exhibit high electrical conductance at room and cryogenic temperatures. Large amounts of graphene sheets in organic solvents are made into large transparent conducting films by Langmuir-Blodgett assembly in a layer-by-layer manner. The chemically derived, high-quality graphene sheets could lead to future scalable graphene devices.

    View details for DOI 10.1038/nnano.2008.210

    View details for Web of Science ID 000259013100010

    View details for PubMedID 18772914

  • Targeted single-wall carbon nanotube-mediated Pt(IV) prodrug delivery using folate as a homing device JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Dhar, S., Liu, Z., Thomale, J., Dai, H., Lippard, S. J. 2008; 130 (34): 11467-11476

    Abstract

    Most low-molecular-weight platinum anticancer drugs have short blood circulation times that are reflected in their reduced tumor uptake and intracellular DNA binding. A platinum(IV) complex of the formula c, c, t-[Pt(NH 3) 2Cl 2(O 2CCH 2CH 2CO 2H)(O 2CCH 2CH 2CONH-PEG-FA)] ( 1), containing a folate derivative (FA) at an axial position, was prepared and characterized. Folic acid offers a means of targeting human cells that highly overexpress the folate receptor (FR). Compound 1 was attached to the surface of an amine-functionalized single-walled carbon nanotube (SWNT-PL-PEG-NH 2) through multiple amide linkages to use the SWNTs as a "longboat delivery system" for the platinum warhead, carrying it to the tumor cell and releasing cisplatin upon intracellular reduction of Pt(IV) to Pt(II). The ability of SWNT tethered 1 to destroy selectively FR(+) vs FR(-) cells demonstrated its ability to target tumor cells that overexpress the FR on their surface. That the SWNTs deliver the folate-bearing Pt(IV) cargos into FR(+) cancer cells by endocytosis was demonstrated by the localization of fluorophore-labeled SWNTs using fluorescence microscopy. Once inside the cell, cisplatin, formed upon reductive release from the longboat oars, enters the nucleus and reacts with its target nuclear DNA, as determined by platinum atomic absorption spectroscopy of cell extracts. Formation of the major cisplatin 1,2-intrastrand d(GpG) cross-links on the nuclear DNA was demonstrated by use of a monoclonal antibody specific for this adduct. The SWNT-tethered compound 1 is the first construct in which both the targeting and delivery moieties have been incorporated into the same molecule; it is also the first demonstration that intracellular reduction of a Pt(IV) prodrug leads to the cis-{Pt((NH 3) 2} 1,2-intrastrand d(GpG) cross-link in nuclear DNA.

    View details for DOI 10.1021/ja803036e

    View details for Web of Science ID 000258660600046

    View details for PubMedID 18661990

  • PEGylated nanographene oxide for delivery of water-insoluble cancer drugs JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Liu, Z., Robinson, J. T., Sun, X., Dai, H. 2008; 130 (33): 10876-?

    Abstract

    It is known that many potent, often aromatic drugs are water insoluble, which has hampered their use for disease treatment. In this work, we functionalized nanographene oxide (NGO), a novel graphitic material, with branched polyethylene glycol (PEG) to obtain a biocompatible NGO-PEG conjugate stable in various biological solutions, and used them for attaching hydrophobic aromatic molecules including a camptothecin (CPT) analogue, SN38, noncovalently via pi-pi stacking. The resulting NGO-PEG-SN38 complex exhibited excellent water solubility while maintaining its high cancer cell killing potency similar to that of the free SN38 molecules in organic solvents. The efficacy of NGO-PEG-SN38 was far higher than that of irinotecan (CPT-11), a FDA-approved water soluble SN38 prodrug used for the treatment of colon cancer. Our results showed that graphene is a novel class of material promising for biological applications including future in vivo cancer treatment with various aromatic, low-solubility drugs.

    View details for DOI 10.1021/ja803688x

    View details for Web of Science ID 000258415900023

    View details for PubMedID 18661992

  • Drug delivery with carbon nanotubes for in vivo cancer treatment CANCER RESEARCH Liu, Z., Chen, K., Davis, C., Sherlock, S., Cao, Q., Chen, X., Dai, H. 2008; 68 (16): 6652-6660

    Abstract

    Chemically functionalized single-walled carbon nanotubes (SWNT) have shown promise in tumor-targeted accumulation in mice and exhibit biocompatibility, excretion, and little toxicity. Here, we show in vivo SWNT drug delivery for tumor suppression in mice. We conjugate paclitaxel (PTX), a widely used cancer chemotherapy drug, to branched polyethylene glycol chains on SWNTs via a cleavable ester bond to obtain a water-soluble SWNT-PTX conjugate. SWNT-PTX affords higher efficacy in suppressing tumor growth than clinical Taxol in a murine 4T1 breast cancer model, owing to prolonged blood circulation and 10-fold higher tumor PTX uptake by SWNT delivery likely through enhanced permeability and retention. Drug molecules carried into the reticuloendothelial system are released from SWNTs and excreted via biliary pathway without causing obvious toxic effects to normal organs. Thus, nanotube drug delivery is promising for high treatment efficacy and minimum side effects for future cancer therapy with low drug doses.

    View details for DOI 10.1158/0008-5472.CAN-08-1468

    View details for Web of Science ID 000258548200022

    View details for PubMedID 18701489

  • Complement activation by PEGylated single-walled carbon nanotubes is independent of C1q and alternative pathway turnover MOLECULAR IMMUNOLOGY Hamad, I., Hunter, A. C., Rutt, K. J., Liu, Z., Dai, H., Moghimi, S. M. 2008; 45 (14): 3797-3803

    Abstract

    We have investigated the interaction between long circulating poly(ethylene glycol)-stabilized single-walled carbon nanotubes (SWNTs) and the complement system. Aminopoly(ethylene glycol)(5000)-distearoylphosphatidylethanolamine (aminoPEG(5000)-DSPE) and methoxyPEG(5000)-DSPE coated as-grown HIPco SWNTs activated complement in undiluted normal human serum as reflected in significant rises in C4d and SC5b-9 levels, but not the alternative pathway split-product Bb, thus indicating activation exclusively through C4 cleavage. Studies in C2-depleted serum confirmed that PEGylated nanotube-mediated elevation of SC5b-9 was C4b2a convertase-dependent. With the aid of monoclonal antibodies against C1s and human serum depleted from C1q, nanotube-mediated complement activation in C1q-depleted serum was also shown to be independent of classical pathway. Nanotube-mediated C4d elevation in C1q-depleted serum, however, was inhibited by N-acetylglucosamine, Futhan (a broad-spectrum serine protease inhibitor capable of preventing complement activation through all three pathways) and anti-MASP-2 antibodies; this strongly suggests a role for activation of MASP-2 in subsequent C4 cleavage and assembly of C4b2a covertases. Intravenous injection of PEGylated nanotubes in some rats was associated with a significant rise in plasma thromboxane B2 levels, indicative of in vivo nanotube-mediated complement activation. The clinical implications of these observations are discussed.

    View details for DOI 10.1016/j.molimm.2008.05.020

    View details for Web of Science ID 000259473900013

    View details for PubMedID 18602161

  • Atomic layer deposition of metal oxides on pristine and functionalized graphene JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Wang, X., Tabakman, S. M., Dai, H. 2008; 130 (26): 8152-?

    Abstract

    We investigate atomic layer deposition (ALD) of metal oxide on pristine and functionalized graphene. On pristine graphene, ALD coating can only actively grow on edges and defect sites, where dangling bonds or surface groups react with ALD precursors. This affords a simple method to decorate and probe single defect sites in graphene planes. We used perylene tetracarboxylic acid (PTCA) to functionalize the graphene surface and selectively introduced densely packed surface groups on graphene. Uniform ultrathin ALD coating on PTCA graphene was achieved over a large area. The functionalization method could be used to integrate ultrathin high-kappa dielectrics in future graphene electronics.

    View details for DOI 10.1021/ja8023059

    View details for Web of Science ID 000257152800022

    View details for PubMedID 18529002

  • Carrier scattering in graphene nanoribbon field-effect transistors APPLIED PHYSICS LETTERS Ouyang, Y., Wang, X., Dai, H., Guo, J. 2008; 92 (24)

    View details for DOI 10.1063/1.2949749

    View details for Web of Science ID 000256934900098

  • Room-temperature all-semiconducting sub-10-nm graphene nanoribbon field-effect transistors PHYSICAL REVIEW LETTERS Wang, X., Ouyang, Y., Li, X., Wang, H., Guo, J., Dai, H. 2008; 100 (20)

    Abstract

    Sub-10 nm wide graphene nanoribbon field-effect transistors (GNRFETs) are studied systematically. All sub-10 nm GNRs afforded semiconducting FETs without exception, with Ion/Ioff ratio up to 10(6) and on-state current density as high as approximately 2000 microA/microm. We estimated carrier mobility approximately 200 cm2/V s and scattering mean free path approximately 10 nm in sub-10 nm GNRs. Scattering mechanisms by edges, acoustic phonon, and defects are discussed. The sub-10 nm GNRFETs are comparable to small diameter (d< or = approximately 1.2 nm) carbon nanotube FETs with Pd contacts in on-state current density and Ion/Ioff ratio, but have the advantage of producing all-semiconducting devices.

    View details for DOI 10.1103/PhysRevLett.100.206803

    View details for Web of Science ID 000256206400058

    View details for PubMedID 18518566

  • Optical properties of ultrashort semiconducting single-walled carbon nanotube capsules down to sub-10 nm JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Sun, X., Zaric, S., Daranciang, D., Welsher, K., Lu, Y., Li, X., Dai, H. 2008; 130 (20): 6551-6555

    Abstract

    Single-walled carbon nanotubes (SWNTs) are typically long (greater than or approximately equal 100 nm) and have been well established as novel quasi one-dimensional systems with interesting electrical, mechanical, and optical properties. Here, quasi zero-dimensional SWNTs with finite lengths down to the molecular scale (7.5 nm in average) were obtained by length separation using a density gradient ultracentrifugation method. Different sedimentation rates of nanotubes with different lengths in a density gradient were taken advantage of to sort SWNTs according to length. Optical experiments on the SWNT fractions revealed that the UV-vis-NIR absorption and photoluminescence peaks of the ultrashort SWNTs blue-shift up to approximately 30 meV compared to long nanotubes, owing to quantum confinement effects along the length of ultrashort SWNTs. These nanotube capsules essentially correspond to SWNT quantum dots.

    View details for DOI 10.1021/ja8006929

    View details for Web of Science ID 000255854100049

    View details for PubMedID 18426207

  • Peptide-coated nanotube-based biosensor for the detection of disease-specific autoantibodies in human serum BIOSENSORS & BIOELECTRONICS Drouvalakis, K. A., Bangsaruntip, S., Hueber, W., Kozar, L. G., Utz, P. J., Dai, H. 2008; 23 (10): 1413-1421

    Abstract

    We demonstrate a label-free peptide-coated carbon nanotube-based immunosensor for the direct assay of human serum. A rheumatoid arthritis (RA)-specific (cyclic citrulline-containing) peptide, was immobilized to functionalized single-walled carbon nanotubes deposited on a quartz crystal microbalance (QCM) sensing crystal. Serum from RA patients was used to probe these nanotube-based sensors, and antibody binding was detected by QCM sensing. Specific antibody binding was also determined by comparing the assay of two serum control groups (normal and diseased sera), and the native unmodified peptide. The sensitivity of the nanotube-based sensor (detection in the femtomol range) was higher than that of the established ELISA and recently described microarray assay systems, detecting 34.4 and 37.5% more RA patients with anti-citrullinated peptide antibodies than those found by ELISA and microarray, respectively. There was also an 18.4 and 19.6% greater chance of a negative test being a true indicator of a person not having RA than by either ELISA or microarray, respectively. The performance of our label-free biosensor enables its application in the direct assay of sera in research and diagnostics.

    View details for DOI 10.1016/j.bios.2007.11.022

    View details for Web of Science ID 000255793200001

    View details for PubMedID 18222083

  • A pilot toxicology study of single-walled carbon nanotubes in a small sample of mice NATURE NANOTECHNOLOGY Schipper, M. L., Nakayama-Ratchford, N., Davis, C. R., Kam, N. W., Chu, P., Liu, Z., Sun, X., Dai, H., Gambhir, S. S. 2008; 3 (4): 216-221

    Abstract

    Single-walled carbon nanotubes are currently under evaluation in biomedical applications, including in vivo delivery of drugs, proteins, peptides and nucleic acids (for gene transfer or gene silencing), in vivo tumour imaging and tumour targeting of single-walled carbon nanotubes as an anti-neoplastic treatment. However, concerns about the potential toxicity of single-walled carbon nanotubes have been raised. Here we examine the acute and chronic toxicity of functionalized single-walled carbon nanotubes when injected into the bloodstream of mice. Survival, clinical and laboratory parameters reveal no evidence of toxicity over 4 months. Upon killing, careful necropsy and tissue histology show age-related changes only. Histology and Raman microscopic mapping demonstrate that functionalized single-walled carbon nanotubes persisted within liver and spleen macrophages for 4 months without apparent toxicity. Although this is a preliminary study with a small group of animals, our results encourage further confirmation studies with larger groups of animals.

    View details for DOI 10.1038/nnano.2008.68

    View details for Web of Science ID 000254744300013

    View details for PubMedID 18654506

  • Chemically derived, ultrasmooth graphene nanoribbon semiconductors SCIENCE Li, X., Wang, X., Zhang, L., Lee, S., Dai, H. 2008; 319 (5867): 1229-1232

    Abstract

    We developed a chemical route to produce graphene nanoribbons (GNR) with width below 10 nanometers, as well as single ribbons with varying widths along their lengths or containing lattice-defined graphene junctions for potential molecular electronics. The GNRs were solution-phase-derived, stably suspended in solvents with noncovalent polymer functionalization, and exhibited ultrasmooth edges with possibly well-defined zigzag or armchair-edge structures. Electrical transport experiments showed that, unlike single-walled carbon nanotubes, all of the sub-10-nanometer GNRs produced were semiconductors and afforded graphene field effect transistors with on-off ratios of about 10(7) at room temperature.

    View details for DOI 10.1126/science.1150878

    View details for Web of Science ID 000253530600039

    View details for PubMedID 18218865

  • Assessment of chemically separated carbon nanotubes for nanoelectronics JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Zhang, L., Zaric, S., Tu, X., Wang, X., Zhao, W., Dai, H. 2008; 130 (8): 2686-2691

    Abstract

    It remains an elusive goal to obtain high performance single-walled carbon-nanotube (SWNT) electronics such as field effect transistors (FETs) composed of single- or few-chirality SWNTs, due to broad distributions in as-grown materials. Much progress has been made by various separation approaches to obtain materials enriched in metal or semiconducting nanotubes or even in single chiralties. However, research in validating SWNT separations by electrical transport measurements and building functional electronic devices has been scarce. Here, we performed length, diameter, and chirality separation of DNA functionalized HiPco SWNTs by chromatography methods, and we characterized the chiralities by photoluminescence excitation spectroscopy, optical absorption spectroscopy, and electrical transport measurements. The use of these combined methods provided deeper insight to the degree of separation than either technique alone. Separation of SWNTs by chirality and diameter occurred at varying degrees that decreased with increasing tube diameter. This calls for new separation methods capable of metallicity or chirality separation of large diameter SWNTs (in the approximately 1.5 nm range) needed for high performance nanoelectronics. With most of the separated fractions enriched in semiconducting SWNTs, nanotubes placed in parallel in short-channel (approximately 200 nm) electrical devices fail to produce FETs with high on/off switching, indicating incomplete elimination of metallic species. In rare cases with a certain separated SWNT fraction, we were able to fabricate FET devices composed of small-diameter, chemically separated SWNTs in parallel, with high on-/off-current (I(on)/I(off)) ratios up to 105 owing to semiconducting SWNTs with only a few (n,m) chiralities in the fraction. This was the first time that chemically separated SWNTs were used for short channel, all-semiconducting SWNT electronics dominant by just a few (n,m)'s. Nevertheless, the results suggest that much improved chemical separation methods are needed to produce nanotube electronics at a large scale.

    View details for DOI 10.1021/ja7106492

    View details for Web of Science ID 000253400900071

    View details for PubMedID 18251484

  • Circulation and long-term fate of functionalized, biocompatible single-walled carbon nanotubes in mice probed by Raman spectroscopy PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Liu, Z., Davis, C., Cai, W., He, L., Chen, X., Dai, H. 2008; 105 (5): 1410-1415

    Abstract

    Carbon nanotubes are promising new materials for molecular delivery in biological systems. The long-term fate of nanotubes intravenously injected into animals in vivo is currently unknown, an issue critical to potential clinical applications of these materials. Here, using the intrinsic Raman spectroscopic signatures of single-walled carbon nanotubes (SWNTs), we measured the blood circulation of intravenously injected SWNTs and detect SWNTs in various organs and tissues of mice ex vivo over a period of three months. Functionalization of SWNTs by branched polyethylene-glycol (PEG) chains was developed, enabling thus far the longest SWNT blood circulation up to 1 day, relatively low uptake in the reticuloendothelial system (RES), and near-complete clearance from the main organs in approximately 2 months. Raman spectroscopy detected SWNT in the intestine, feces, kidney, and bladder of mice, suggesting excretion and clearance of SWNTs from mice via the biliary and renal pathways. No toxic side effect of SWNTs to mice was observed in necropsy, histology, and blood chemistry measurements. These findings pave the way to future biomedical applications of carbon nanotubes.

    View details for DOI 10.1073/pnas.0707654105

    View details for Web of Science ID 000253077900007

    View details for PubMedID 18230737

  • Selective probing and imaging of cells with single walled carbon nanotubes as near-infrared fluorescent molecules NANO LETTERS Welsher, K., Liu, Z., Daranciang, D., Dai, H. 2008; 8 (2): 586-590

    Abstract

    Fluorescent molecules emitting in the near-infrared (NIR, wavelength approximately 0.8-2 microm) are relatively scarce and have been actively sought for biological applications because cells and tissues exhibit little auto-fluorescence in this region. Here, we report the use of semiconducting single-walled carbon nanotubes (SWNTs) as near-infrared fluorescent tags for selective probing of cell surface receptors and cell imaging. Biologically inert SWNTs with polyethyleneglycol functionalization are conjugated to antibodies such as Rituxan to selectively recognize CD20 cell surface receptor on B-cells with little nonspecific binding to negative T-cells and Herceptin to recognize HER2/neu positive breast cancer cells. We image selective SWNT-antibody binding to cells by detecting the intrinsic NIR photoluminescence of nanotubes. We observe ultralow NIR autofluorescence for various cells, an advantageous feature over high autofluorescence and large variations between cells lines in the visible. This establishes SWNTs as novel NIR fluorophors for sensitive and selective biological detections and imaging in vitro and potentially in vivo. Further, our results clearly show that the interactions between carbon nanotubes and living cells are strongly dependent on surface functionalization of nanotubes.

    View details for DOI 10.1021/nl072949q

    View details for Web of Science ID 000253166200039

    View details for PubMedID 18197719

  • Hydrogen storage in carbon nanotubes through the formation of stable C-H bonds NANO LETTERS Nikitin, A., Li, X., Zhang, Z., Ogasawara, H., Dai, H., Nilsson, A. 2008; 8 (1): 162-167

    Abstract

    To determine if carbon-based materials can be used for hydrogen storage, we have studied hydrogen chemisorption in single-walled carbon nanotubes. Using atomic hydrogen as the hydrogenation agent, we demonstrated that maximal degree of nanotube hydrogenation depends on the nanotube diameter, and for the diameter values around 2.0 nm nanotube-hydrogen complexes with close to 100% hydrogenation exist and are stable at room temperature. This means that specific carbon nanotubes can have a hydrogen storage capacity of more than 7 wt % through the formation of reversible C-H bonds.

    View details for DOI 10.1021/nl072325k

    View details for Web of Science ID 000252257700029

    View details for PubMedID 18088150

  • Carbon nanotube synthesis and organization CARBON NANOTUBES Joselevich, E., Dai, H., Liu, J., Hata, K., Windle, A. H. 2008; 111: 101-164
  • Selective synthesis combined with chemical separation of single-walled carbon nanotubes for chirality selection JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Li, X., Tu, X., Zaric, S., Welsher, K., Seo, W. S., Zhao, W., Dai, H. 2007; 129 (51): 15770-?

    Abstract

    Single-walled carbon nanotubes (SWNTs) are potential materials for future nanoelectronics. Since the electronic and optical properties of SWNTs strongly depend on tube diameter and chirality, obtaining SWNTs with narrow (n,m) chirality distribution by selective growth or chemical separation has been an active area of research. Here, we demonstrate that a new, bimetallic FeRu catalyst affords SWNT growth with narrow diameter and chirality distribution in methane CVD. At 600 degrees C, methane CVD on FeRu catalyst produced predominantly (6,5) SWNTs according to UV-vis-NIR absorption and photoluminescence excitation/emission (PLE) spectroscopic characterization. At 850 degrees C, the dominant semiconducting species produced are (8,4), (7,6), and (7,5) SWNTs, with much narrower distributions in diameter and chirality than materials grown by other catalysts. Further, we show that narrow diameter/chirality growth combined with chemical separation by ion exchange chromatography (IEC) greatly facilitates achieving single (m,n) SWNT samples, as demonstrated by obtaining highly enriched (8,4) SWNTs with near elimination of metallic SWNTs existing in the as-grown material.

    View details for DOI 10.1021/ja077886s

    View details for Web of Science ID 000251974000021

    View details for PubMedID 18052285

  • Electrically driven light emission from hot single-walled carbon nanotubes at various temperatures and ambient pressures APPLIED PHYSICS LETTERS Wang, X., Zhang, L., Lu, Y., Dai, H., Kato, Y. K., Pop, E. 2007; 91 (26)

    View details for DOI 10.1063/1.2827281

    View details for Web of Science ID 000251987400002

  • Theoretical investigations on thermal light emission from metallic carbon nanotubes IEEE TRANSACTIONS ON NANOTECHNOLOGY Ouyang, Y., Mann, D., Dai, H., Guo, J. 2007; 6 (6): 682-687
  • Supramolecular chemistry on water-soluble carbon nanotubes for drug loading and delivery ACS NANO Liu, Z., Sun, X., Nakayama-Ratchford, N., Dai, H. 2007; 1 (1): 50-56

    Abstract

    We show that large surface areas exist for supramolecular chemistry on single-walled carbon nanotubes (SWNTs) prefunctionalized noncovalently or covalently by common surfactant or acid-oxidation routes. Water-soluble SWNTs with poly(ethylene glycol) (PEG) functionalization via these routes allow for surprisingly high degrees of pi-stacking of aromatic molecules, including a cancer drug (doxorubicin) with ultrahigh loading capacity, a widely used fluorescence molecule (fluorescein), and combinations of molecules. Binding of molecules to nanotubes and their release can be controlled by varying the pH. The strength of pi-stacking of aromatic molecules is dependent on nanotube diameter, leading to a method for controlling the release rate of molecules from SWNTs by using nanotube materials with suitable diameter. This work introduces the concept of "functionalization partitioning" of SWNTs, i.e., imparting multiple chemical species, such as PEG, drugs, and fluorescent tags, with different functionalities onto the surface of the same nanotube. Such chemical partitioning should open up new opportunities in chemical, biological, and medical applications of novel nanomaterials.

    View details for DOI 10.1021/nn700040t

    View details for Web of Science ID 000252012200011

    View details for PubMedID 19203129

  • Tomonaga-luttinger liquid features in ballistic single-walled carbon nanotubes: Conductance and shot noise PHYSICAL REVIEW LETTERS Kim, N. Y., Recher, P., Oliver, W. D., Yamamoto, Y., Kong, J., Dai, H. 2007; 99 (3)

    Abstract

    We study the electrical transport properties of well-contacted ballistic single-walled carbon nanotubes in a three-terminal configuration at low temperatures. We observe signatures of strong electron-electron interactions: the conductance exhibits bias-voltage-dependent amplitudes of quantum interference oscillation, and both the current noise and Fano factor manifest bias-voltage-dependent power-law scalings. We analyze our data within the Tomonaga-Luttinger liquid model using the nonequilibrium Keldysh formalism and find qualitative and quantitative agreement between experiment and theory.

    View details for DOI 10.1103/PhyRevLett.99.036802

    View details for Web of Science ID 000248194700038

    View details for PubMedID 17678308

  • Soluble single-walled carbon nanotubes as longboat delivery systems for Platinum(IV) anticancer drug design JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Feazell, R. P., Nakayama-Ratchford, N., Dai, H., Lippard, S. J. 2007; 129 (27): 8438-?

    View details for DOI 10.1021/ja073231f

    View details for Web of Science ID 000247759400020

    View details for PubMedID 17569542

  • Measuring the capacitance of individual semiconductor nanowires for carrier mobility assessment NANO LETTERS Tu, R., Zhang, L., Nishi, Y., Dai, H. 2007; 7 (6): 1561-1565

    Abstract

    Capacitance-voltage characteristics of individual germanium nanowire field effect transistors were directly measured and used to assess carrier mobility in nanowires for the first time, thereby removing uncertainties in calculated mobility due to device geometries, surface and interface states, and gate dielectric constants and thicknesses. Direct experimental evidence showed that surround-gated nanowire transistors exhibit higher capacitance and better electrostatic gate control than top-gated devices, and are the most promising structure for future high performance nanoelectronics.

    View details for DOI 10.1021/nl070378w

    View details for Web of Science ID 000247186800023

    View details for PubMedID 17488051

  • Electrical and thermal transport in metallic single-wall carbon nanotubes on insulating substrates JOURNAL OF APPLIED PHYSICS Pop, E., Mann, D. A., Goodson, K. E., Dai, H. 2007; 101 (9)

    View details for DOI 10.1063/1.2717855

    View details for Web of Science ID 000246567900049

  • Langmuir-Blodgett assembly of densely aligned single-walled carbon nanotubes from bulk materials JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Li, X., Zhang, L., Wang, X., Shimoyama, I., Sun, X., Seo, W., Dai, H. 2007; 129 (16): 4890-?

    View details for DOI 10.1021/ja071114e

    View details for Web of Science ID 000245782800017

    View details for PubMedID 17394327

  • Noncovalent functionalization of carbon nanotubes by fluorescein-polyethylene glycol: Supramolecular conjugates with pH-dependent absorbance and fluorescence JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Nakayama-Ratchford, N., Bangsaruntip, S., Sun, X., Welsher, K., Dai, H. 2007; 129 (9): 2448-?

    View details for DOI 10.1021/ja068684j

    View details for Web of Science ID 000244731300020

    View details for PubMedID 17284037

  • siRNA delivery into human T cells and primary cells with carbon-nanotube transporters ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Liu, Z., Winters, M., Holodniy, M., Dai, H. 2007; 46 (12): 2023-2027

    View details for DOI 10.1002/anie.200604295

    View details for Web of Science ID 000245071000016

    View details for PubMedID 17290476

  • In vivo biodistribution and highly efficient tumour targeting of carbon nanotubes in mice NATURE NANOTECHNOLOGY Liu, Z., Cai, W., He, L., Nakayama, N., Chen, K., Sun, X., Chen, X., Dai, H. 2007; 2 (1): 47-52

    View details for DOI 10.1038/nnano.2006.170

    View details for Web of Science ID 000243902900015

    View details for PubMedID 18654207

  • Electrically driven thermal light emission from individual single-walled carbon nanotubes NATURE NANOTECHNOLOGY Mann, D., Kato, Y. K., Kinkhabwala, A., Pop, E., Cao, J., Wang, X., Zhang, L., Wang, Q., Guo, J., Dai, H. 2007; 2 (1): 33-38

    View details for DOI 10.1038/nnano.2006.169

    View details for Web of Science ID 000243902900012

    View details for PubMedID 18654204

  • Parallel core-shell metal-dielectric-semiconductor germanium nanowires for high-current surround-gate field-effect transistors NANO LETTERS Zhang, L., Tu, R., Dai, H. 2006; 6 (12): 2785-2789

    Abstract

    Core-shell germanium nanowires (GeNW) are formed with a single-crystalline Ge core and concentric shells of nitride and silicon passivation layer by chemical vapor deposition (CVD), an Al2O3 gate dielectric layer by atomic layer deposition (ALD), and an Al metal surround-gate (SG) shell by isotropic magnetron sputter deposition. Surround-gate nanowire field-effect transistors (FETs) are then constructed using a novel self-aligned fabrication approach. Individual SG GeNW FETs show improved switching over GeNW FETs with planar gate stacks owing to improved electrostatics. FET devices comprised of multiple quasi-aligned SG GeNWs in parallel are also constructed. Collectively, tens of SG GeNWs afford on-currents exceeding 0.1 mA at low source-drain bias voltages. The self-aligned surround-gate scheme can be generalized to various semiconductor nanowire materials.

    View details for DOI 10.1021/nl061833b

    View details for Web of Science ID 000242786500027

    View details for PubMedID 17163706

  • FeCo/graphitic-shell nanocrystals as advanced magnetic-resonance-imaging and near-infrared agents NATURE MATERIALS Seo, W. S., Lee, J. H., Sun, X., Suzuki, Y., Mann, D., Liu, Z., Terashima, M., Yang, P. C., McConnell, M. V., Nishimura, D. G., Dai, H. 2006; 5 (12): 971-976

    Abstract

    Nanocrystals with advanced magnetic or optical properties have been actively pursued for potential biological applications, including integrated imaging, diagnosis and therapy. Among various magnetic nanocrystals, FeCo has superior magnetic properties, but it has yet to be explored owing to the problems of easy oxidation and potential toxicity. Previously, FeCo nanocrystals with multilayered graphitic carbon, pyrolytic carbon or inert metals have been obtained, but not in the single-shelled, discrete, chemically functionalized and water-soluble forms desired for biological applications. Here, we present a scalable chemical vapour deposition method to synthesize FeCo/single-graphitic-shell nanocrystals that are soluble and stable in water solutions. We explore the multiple functionalities of these core-shell materials by characterizing the magnetic properties of the FeCo core and near-infrared optical absorbance of the single-layered graphitic shell. The nanocrystals exhibit ultra-high saturation magnetization, r1 and r2 relaxivities and high optical absorbance in the near-infrared region. Mesenchymal stem cells are able to internalize these nanoparticles, showing high negative-contrast enhancement in magnetic-resonance imaging (MRI). Preliminary in vivo experiments achieve long-lasting positive-contrast enhancement for vascular MRI in rabbits. These results point to the potential of using these nanocrystals for integrated diagnosis and therapeutic (photothermal-ablation) applications.

    View details for DOI 10.1038/nmat1775

    View details for Web of Science ID 000242478600021

    View details for PubMedID 17115025

  • Selective etching of metallic carbon nanotubes by gas-phase reaction SCIENCE Zhang, G., Qi, P., Wang, X., Lu, Y., Li, X., Tu, R., Bangsaruntip, S., Mann, D., Zhang, L., Dai, H. 2006; 314 (5801): 974-977

    Abstract

    Metallic and semiconducting carbon nanotubes generally coexist in as-grown materials. We present a gas-phase plasma hydrocarbonation reaction to selectively etch and gasify metallic nanotubes, retaining the semiconducting nanotubes in near-pristine form. With this process, 100% of purely semiconducting nanotubes were obtained and connected in parallel for high-current transistors. The diameter- and metallicity-dependent "dry" chemical etching approach is scalable and compatible with existing semiconductor processing for future integrated circuits.

    View details for DOI 10.1126/science.1133781

    View details for Web of Science ID 000241896000047

    View details for PubMedID 17095698

  • Single walled carbon nanotubes for transport and delivery of biological cargos PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS Kam, N. W., Dai, H. 2006; 243 (13): 3561-3566
  • Neural stimulation with a carbon nanotube microelectrode array NANO LETTERS Wang, K., Fishman, H. A., Dai, H., Harris, J. S. 2006; 6 (9): 2043-2048

    Abstract

    We present a novel prototype neural interface using vertically aligned multiwalled carbon nanotube (CNT) pillars as microelectrodes. Functionalized hydrophilic CNT microelectrodes offer a high charge injection limit (1-1.6 mC/cm2) without faradic reactions. The first repeated in vitro stimulation of hippocampal neurons with CNT electrodes is demonstrated. These results suggest that CNTs are capable of providing far safer and more efficacious solutions for neural prostheses than previous metal electrode approaches.

    View details for DOI 10.1021/nl061241t

    View details for Web of Science ID 000240465100037

    View details for PubMedID 16968023

  • Electrical transport properties and field effect transistors of carbon nanotubes NANO Dai, H., Javey, A., Pop, E., Mann, D., Kim, W., Lu, Y. 2006; 1 (1): 1-13
  • Hydrogenation and hydrocarbonation and etching of single-walled carbon nanotubes JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Zhang, G., Qi, P., Wang, X., Lu, Y., Mann, D., Li, X., Dai, H. 2006; 128 (18): 6026-6027

    Abstract

    We present a systematic experimental investigation of the reactions between hydrogen plasma and single-walled carbon nanotubes (SWNTs) at various temperatures. Microscopy, infrared (IR) and Raman spectroscopy, and electrical transport measurements are carried out to investigate the properties of SWNTs after hydrogenation. Structural deformations, drastically reduced electrical conductance, and an increased semiconducting nature of SWNTs upon sidewall hydrogenation are observed. These changes are reversible upon thermal annealing at 500 degrees C via dehydrogenation. Harsh plasma or high temperature reactions lead to etching of nanotubes likely via hydrocarbonation. Smaller SWNTs are markedly less stable against hydrocarbonation than larger tubes. The results are fundamental and may have implications to basic and practical applications including hydrogen storage, sensing, band gap engineering for novel electronics, and new methods of manipulation, functionalization, and etching of nanotubes.

    View details for DOI 10.1021/ja061324b

    View details for Web of Science ID 000237468900022

    View details for PubMedID 16669658

  • DNA functionalization of carbon nanotubes for ultrathin atomic layer deposition of high kappa dielectrics for nanotube transistors with 60 mV/decade switching JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Lu, Y. R., Bangsaruntip, S., Wang, X. R., Zhang, L., Nishi, Y., Dai, H. J. 2006; 128 (11): 3518-3519

    Abstract

    For single-walled carbon nanotube (SWNT) field effect transistors, vertical scaling of high kappa dielectrics by atomic layer deposition (ALD) currently stands at approximately 8 nm with a subthreshold swing S approximately 70-90 mV/decade at room temperature. ALD on as-grown pristine SWNTs is incapable of producing a uniform and conformal dielectric layer due to the lack of functional groups on nanotubes and because nucleation of an oxide dielectric layer in the ALD process hinges upon covalent chemisorption on reactive groups on surfaces. Here, we show that by noncovalent functionalization of SWNTs with poly-T DNA molecules (dT40-DNA), one can impart functional groups of sufficient density and stability for uniform and conformal ALD of high kappa dielectrics on SWNTs with thickness down to 2-3 nm. This enables approaching the ultimate vertical scaling limit of nanotube FETs and reliably achieving S approximately 60 mV/decade at room temperature, and S approximately 50 mV/decade in the band-to-band tunneling regime of ambipolar transport. We have also carried out microscopy investigations to understand ALD processes on SWNTs with and without DNA functionalization.

    View details for DOI 10.1021/ja058836v

    View details for Web of Science ID 000236299700024

    View details for PubMedID 16536515

  • Carbon nanotubes as intracellular transporters for proteins and DNA: An investigation of the uptake mechanism and pathway ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Kam, N. W., Liu, Z. A., Dai, H. J. 2006; 45 (4): 577-581

    View details for DOI 10.1002/anie.200503389

    View details for Web of Science ID 000234769200008

    View details for PubMedID 16345107

  • Carbon nanotubes: From growth, placement and assembly control to 60mV/decade and sub-60 mV/decade tunnel transistors 2006 INTERNATIONAL ELECTRON DEVICES MEETING, VOLS 1 AND 2 Zhang, G., Wang, X., Li, X., Lu, Y., Javey, A., Dai, H. 2006: 160-163
  • Thermal conductance of an individual single-wall carbon nanotube above room temperature NANO LETTERS Pop, E., Mann, D., Wang, Q., Goodson, K. E., Dai, H. J. 2006; 6 (1): 96-100

    Abstract

    The thermal properties of a suspended metallic single-wall carbon nanotube (SWNT) are extracted from its high-bias (I-V) electrical characteristics over the 300-800 K temperature range, achieved by Joule self-heating. The thermal conductance is approximately 2.4 nW/K, and the thermal conductivity is nearly 3500 Wm(-1)K(-1) at room temperature for a SWNT of length 2.6 mum and diameter 1.7 nm. A subtle decrease in thermal conductivity steeper than 1/T is observed at the upper end of the temperature range, which is attributed to second-order three-phonon scattering between two acoustic modes and one optical mode. We discuss sources of uncertainty and propose a simple analytical model for the SWNT thermal conductivity including length and temperature dependence.

    View details for DOI 10.1021/nl052145f

    View details for Web of Science ID 000235532400018

    View details for PubMedID 16402794

  • Hydrogenation of single-walled carbon nanotubes PHYSICAL REVIEW LETTERS Nikitin, A., Ogasawara, H., Mann, D., Denecke, R., Zhang, Z., Dai, H., Cho, K., Nilsson, A. 2005; 95 (22)

    Abstract

    Towards the development of a useful mechanism for hydrogen storage, we have studied the hydrogenation of single-walled carbon nanotubes with atomic hydrogen using core-level photoelectron spectroscopy and x-ray absorption spectroscopy. We find that atomic hydrogen creates C-H bonds with the carbon atoms in the nanotube walls, and such C-H bonds can be completely broken by heating to 600 degrees C. We demonstrate approximately 65 +/- 15 at % hydrogenation of carbon atoms in the single-walled carbon nanotubes, which is equivalent to 5.1 +/- 1.2 wt % hydrogen capacity. We also show that the hydrogenation is a reversible process.

    View details for DOI 10.1103/PhysRevLett.95.225507

    View details for Web of Science ID 000233458500040

    View details for PubMedID 16384236

  • Ultra-high-yield growth of vertical single-walled carbon nanotubes: Hidden roles of hydrogen and oxygen PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Zhang, G. Y., Mann, D., Zhang, L., Javey, A., Li, Y. M., Yenilmez, E., Wang, Q., McVittie, J. P., Nishi, Y., Gibbons, J., Dai, H. J. 2005; 102 (45): 16141-16145

    Abstract

    An oxygen-assisted hydrocarbon chemical vapor deposition method is developed to afford large-scale, highly reproducible, ultra-high-yield growth of vertical single-walled carbon nanotubes (V-SWNTs). It is revealed that reactive hydrogen species, inevitable in hydrocarbon-based growth, are damaging to the formation of sp(2)-like SWNTs in a diameter-dependent manner. The addition of oxygen scavenges H species and provides a powerful control over the C/H ratio to favor SWNT growth. The revelation of the roles played by hydrogen and oxygen leads to a unified and universal optimum-growth condition for SWNTs. Further, a versatile method is developed to form V-SWNT films on any substrate, lifting a major substrate-type limitation for aligned SWNTs.

    View details for DOI 10.1073/pnas.0507064102

    View details for Web of Science ID 000233283700005

    View details for PubMedID 16263931

  • Negative differential conductance and hot phonons in suspended nanotube molecular wires PHYSICAL REVIEW LETTERS Pop, E., Mann, D., Cao, J., Wang, Q., Goodson, K. E., Dai, H. J. 2005; 95 (15)

    Abstract

    Freely suspended metallic single-walled carbon nanotubes (SWNTs) exhibit reduced current carrying ability compared to those lying on substrates, and striking negative differential conductance at low electric fields. Theoretical analysis reveals significant self-heating effects including electron scattering by hot nonequilibrium optical phonons. Electron transport characteristics under strong self-heating are exploited for the first time to probe the thermal conductivity of individual SWNTs (approximately 3600 W m-1 K-1 at T=300 K) up to approximately 700 K, and reveal a 1/T dependence expected for umklapp phonon scattering at high temperatures.

    View details for DOI 10.1103/PhysRevLett.95.155505

    View details for Web of Science ID 000232443400039

    View details for PubMedID 16241738

  • Electron transport in very clean, as-grown suspended carbon nanotubes NATURE MATERIALS Cao, J., Wang, Q., Dai, H. 2005; 4 (10): 745-749

    Abstract

    Single-walled carbon nanotubes have shown a wealth of quantum transport phenomena thus far. Defect-free, unperturbed single-walled carbon nanotubes with well behaved or tunable metal contacts are important for probing the intrinsic electrical properties of nanotubes. Meeting these conditions experimentally is non-trivial owing to numerous disorder and randomizing factors. Here we show that approximately 1-microm-long fully suspended single-walled carbon nanotubes grown in place between metal contacts afford devices with well defined characteristics over much wider energy ranges than nanotubes pinned on substrates. Various low-temperature transport regimes in true-metallic, small- and large-bandgap semiconducting nanotubes are observed, including quantum states shell-filling, -splitting and -crossing in magnetic fields owing to the Aharonov-Bohm effect. The clean transport data show a correlation between the contact junction resistance and the various transport regimes in single-walled-carbon-nanotube devices. Furthermore, we show that electrical transport data can be used to probe the band structures of nanotubes, including nonlinear band dispersion.

    View details for DOI 10.1038/nmat1478

    View details for Web of Science ID 000232229500012

    View details for PubMedID 16142240

  • Functionalization of carbon nanotubes via cleavable disulfide bonds for efficient intracellular delivery of siRNA and potent gene silencing JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Kam, N. W., Liu, Z., Dai, H. J. 2005; 127 (36): 12492-12493

    Abstract

    We present a novel functionalization scheme for single-walled carbon nanotubes (SWNTs) to afford nanotube-biomolecule conjugates with the incorporation of cleavable bonds to enable controlled molecular releasing from nanotube surfaces, thus creating "smart" nanomaterials with high potential for chemical and biological applications. With this versatile functionalization, we demonstrate transporting, enzymatic cleaving and releasing of DNA from SWNT transporters, and subsequent nuclear translocation of DNA oligonucleotides in mammalian cells. We further show highly efficient delivery of siRNA by SWNTs and achieving more potent RNAi functionality than a widely used conventional transfection agent. Thus, the novel functionalization of SWNTs with cleavable bonds is highly promising for a wide range of applications including gene and protein therapy.

    View details for DOI 10.1021/ja053962k

    View details for Web of Science ID 000232039100030

    View details for PubMedID 16144388

  • Regular arrays of 2 nm metal nanoparticles for deterministic synthesis of nanomaterials JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Javey, A., Dai, H. J. 2005; 127 (34): 11942-11943

    Abstract

    A novel method is developed to enable the formation, positioning, and patterning of individual metal nanoclusters with controllable and monodispersed sizes down to 1-2 nm scale. The method is generic for fabricating designed arrays of virtually any type of metal nanoparticles well below 10 nm. Among the wide range of potential applications in surface and materials science, the nanoparticle arrays are used for deterministic synthesis of monodispersed single-walled carbon nanotubes at individually controlled locations with near 1:1 yield, reaching one of the ultimate goals of nanotube synthesis.

    View details for DOI 10.1021/ja0536668

    View details for Web of Science ID 000231605900032

    View details for PubMedID 16117524

  • Oxidation resistant germanium nanowires: Bulk synthesis, long chain alkanethiol functionalization, and Langmuir-Blodgett assembly JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Wang, D. W., Chang, Y. L., Liu, Z., Dai, H. J. 2005; 127 (33): 11871-11875

    Abstract

    A simple method is developed to synthesize gram quantities of uniform Ge nanowires (GeNWs) by chemical vapor deposition on preformed, monodispersed seed particles loaded onto a high surface area silica support. Various chemical functionalization schemes are investigated to passivate the GeNW surfaces using alkanethiols and alkyl Grignard reactions. The stability of functionalization against oxidation of germanium for various alkyl chain lengths is elucidated by X-ray photoelectron spectroscopy. Among all schemes tested, long chain alkanethiols (> or = C12) are found to impart the most stable GeNW passivation against oxidation upon extended exposure to ambient air. Further, the chemically functionalized oxidation-resistant nanowires are soluble in organic solvents and can be readily assembled into close-packed Langmuir-Blodgett films potentially useful for future high performance electronic devices.

    View details for DOI 10.1021/ja053836g

    View details for Web of Science ID 000231454100074

    View details for PubMedID 16104766

  • Carbon nanotubes as multifunctional biological transporters and near-infrared agents for selective cancer cell destruction PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Kam, N. W., O'Connell, M., Wisdom, J. A., Dai, H. J. 2005; 102 (33): 11600-11605

    Abstract

    Biological systems are known to be highly transparent to 700- to 1,100-nm near-infrared (NIR) light. It is shown here that the strong optical absorbance of single-walled carbon nanotubes (SWNTs) in this special spectral window, an intrinsic property of SWNTs, can be used for optical stimulation of nanotubes inside living cells to afford multifunctional nanotube biological transporters. For oligonucleotides transported inside living cells by nanotubes, the oligos can translocate into cell nucleus upon endosomal rupture triggered by NIR laser pulses. Continuous NIR radiation can cause cell death because of excessive local heating of SWNT in vitro. Selective cancer cell destruction can be achieved by functionalization of SWNT with a folate moiety, selective internalization of SWNTs inside cells labeled with folate receptor tumor markers, and NIR-triggered cell death, without harming receptor-free normal cells. Thus, the transporting capabilities of carbon nanotubes combined with suitable functionalization chemistry and their intrinsic optical properties can lead to new classes of novel nanomaterials for drug delivery and cancer therapy.

    View details for DOI 10.1073/pnas.0502680102

    View details for Web of Science ID 000231317000008

    View details for PubMedID 16087878

  • Carbon nanotubes as intracellular protein transporters: Generality and biological functionality JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Kam, N. W., Dai, H. J. 2005; 127 (16): 6021-6026

    Abstract

    Various proteins adsorb spontaneously on the sidewalls of acid-oxidized single-walled carbon nanotubes. This simple nonspecific binding scheme can be used to afford noncovalent protein-nanotube conjugates. The proteins are found to be readily transported inside various mammalian cells with nanotubes acting as the transporter via the endocytosis pathway. Once released from the endosomes, the internalized protein-nanotube conjugates can enter into the cytoplasm of cells and perform biological functions, evidenced by apoptosis induction by transported cytochrome c. Carbon nanotubes represent a new class of molecular transporters potentially useful for future in vitro and in vivo protein delivery applications.

    View details for DOI 10.1021/ja050062v

    View details for Web of Science ID 000228602600065

    View details for PubMedID 15839702

  • Robustness, scalability, and integration of a wound-response gene expression signature in predicting breast cancer survival PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Chang, H. Y., Nuyten, D. S., Sneddon, J. B., Hastie, T., Tibshirani, R., Sorlie, T., Dai, H. Y., He, Y. D., Van't Veer, L. J., Bartelink, H., van de Rijn, M., Brown, P. O., van de Vijver, M. J. 2005; 102 (10): 3738-3743

    Abstract

    Based on the hypothesis that features of the molecular program of normal wound healing might play an important role in cancer metastasis, we previously identified consistent features in the transcriptional response of normal fibroblasts to serum, and used this "wound-response signature" to reveal links between wound healing and cancer progression in a variety of common epithelial tumors. Here, in a consecutive series of 295 early breast cancer patients, we show that both overall survival and distant metastasis-free survival are markedly diminished in patients whose tumors expressed this wound-response signature compared to tumors that did not express this signature. A gene expression centroid of the wound-response signature provides a basis for prospectively assigning a prognostic score that can be scaled to suit different clinical purposes. The wound-response signature improves risk stratification independently of known clinico-pathologic risk factors and previously established prognostic signatures based on unsupervised hierarchical clustering ("molecular subtypes") or supervised predictors of metastasis ("70-gene prognosis signature").

    View details for DOI 10.1073/pnas.0409462102

    View details for Web of Science ID 000227533100040

    View details for PubMedID 15701700

  • Measurement of ionizing radiation using carbon nanotube field effect transistor PHYSICS IN MEDICINE AND BIOLOGY Tang, X. W., Yang, Y., Kim, W., Wang, Q., Qi, P. F., Dai, H. J., Xing, L. 2005; 50 (3): N23-N31

    Abstract

    Single-walled carbon nanotubes (SWNTs) are a new class of highly promising nanomaterials for future nano-electronics. Here, we present an initial investigation of the feasibility of using SWNT field effect transistors (SWNT-FETs) formed on silicon-oxide substrates and suspended FETs for radiation dosimetry applications. Electrical measurements and atomic force microscopy (AFM) revealed the intactness of SWNT-FET devices after exposure to over 1 Gy of 6 MV therapeutic x-rays. The sensitivity of SWNT-FET devices to x-ray irradiation is elucidated by real-time dose monitoring experiments and accumulated dose reading based on threshold voltage shift. SWNT-FET devices exhibit sensitivities to x-rays that are at least comparable to or orders of magnitude higher than commercial MOSFET (metal-oxide semiconductor field effect transistor) dosimeters and could find applications as miniature dosimeters for microbeam profiling and implantation.

    View details for DOI 10.1088/0031-9155/50/3/N02

    View details for Web of Science ID 000227288400013

    View details for PubMedID 15773731

  • High performance n-type carbon nanotube field-effect transistors with chemically doped contacts NANO LETTERS Javey, A., Tu, R., Farmer, D. B., Guo, J., Gordon, R. G., Dai, H. J. 2005; 5 (2): 345-348

    Abstract

    Short channel ( approximately 80 nm) n-type single-walled carbon nanotube (SWNT) field-effect transistors (FETs) with potassium (K) doped source and drain regions and high-kappa gate dielectrics (ALD HfO(2)) are obtained. For nanotubes with diameter approximately 1.6 nm and band gap approximately 0.55 eV, we obtain n-MOSFET-like devices exhibiting high on-currents due to chemically suppressed Schottky barriers at the contacts, subthreshold swing of 70 mV/decade, negligible ambipolar conduction, and high on/off ratios up to 10(6) at a bias voltage of 0.5 V. The results compare favorably with the state-of-the-art silicon n-MOSFETs and demonstrate the potential of SWNTs for future complementary electronics. The effects of doping level on the electrical characteristics of the nanotube devices are discussed.

    View details for DOI 10.1021/nl047931j

    View details for Web of Science ID 000227100500028

    View details for PubMedID 15794623

  • 2,4-dinitrobenzenesulfonyl fluoresceins as fluorescent alternatives to Ellman's reagent in thiol-quantification enzyme assays ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Maeda, H., Matsuno, H., Ushida, M., Katayama, K., Saeki, K., Itoh, N. 2005; 44 (19): 2922-2925

    View details for DOI 10.1002/anie.200500114

    View details for Web of Science ID 000229091300018

    View details for PubMedID 15818626

  • Deterministic one-to-one synthesis of germanium nanowires and individual gold nanoseed patterning for aligned arrays ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Wang, D. W., Tu, R., Zhang, L., Dai, H. J. 2005; 44 (19): 2925-2929

    View details for Web of Science ID 000229091300019

    View details for PubMedID 20058329

  • Self-aligned 40 nm channel carbon nanotube field-effect transistors with subthreshold swings down to 70mV/decade QUANTUM SENSING AND NANOPHOTONIC DEVICES II Javey, A., Farmer, D., Gordon, R., DAI, H. J. 2005; 5732: 14-18

    View details for DOI 10.1117/12.584212

    View details for Web of Science ID 000229036500002

  • Suspended carbon nanotube quantum wires with two gates SMALL Cao, H., Wang, Q., Wang, D. W., Dai, H. J. 2005; 1 (1): 138-141

    Abstract

    Suspended single-walled carbon nanotube devices comprised of high-quality electrical contacts and two electrostatic gates per device have been prepared. Compared to nanotubes pinned on substrates, the suspended devices exhibit little hysteresis related to environmental factors and act as cleaner Fabry-Perot interferometers or single-electron transistors. The high-field saturation currents in the suspended nanotubes related to optical phonon or zone-boundary phonon scattering are significantly lower due to the lack of efficient heat sinking. The multiple-gate design may also facilitate future investigations into the electromechanical properties of nanotube quantum systems.

    View details for DOI 10.1002/smll.200400015

    View details for Web of Science ID 000229117700021

    View details for PubMedID 17193364

  • Aharonov-bohm interference and beating in single-walled carbon-nanotube interferometers PHYSICAL REVIEW LETTERS Cao, J., Wang, Q., Rolandi, M., Dai, H. J. 2004; 93 (21)

    Abstract

    Relatively low magnetic fields applied parallel to the axis of a chiral single-walled carbon nanotube are found causing large modulations to the p channel or valence band conductance of the nanotube in the Fabry-Perot interference regime. Beating in the Aharonov-Bohm type of interference between two field-induced nondegenerate subbands of spiraling electrons is responsible for the observed modulation with a pseudoperiod much smaller than that needed to reach the flux quantum Phi0 = h/e through the nanotube cross section. We show that single-walled nanotubes represent the smallest cylinders exhibiting the Aharonov-Bohm effect with rich interference and beating phenomena arising from well-defined molecular orbitals reflective of the nanotube chirality.

    View details for DOI 10.1103/PhysRevLett.93.216803

    View details for Web of Science ID 000225220500065

    View details for PubMedID 15601048

  • Miniature organic transistors with carbon nanotubes as quasi-one-dimensional electrodes JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Qi, P. F., Javey, A., Rolandi, M., Wang, Q., Yenilmez, E., Dai, H. J. 2004; 126 (38): 11774-11775

    Abstract

    As the dimensions of electronic devices approach those of molecules, the size, geometry, and chemical composition of the contact electrodes play increasingly dominant roles in device functions. It is shown here that single-walled carbon nanotubes (SWNT) can be used as quasi-one-dimensional (1D) electrodes to construct organic field effect transistors (FET) with molecular scale width ( approximately 2 nm) and channel length (1-3 nm). An important feature owing to the quasi-1D electrode geometry is the favorable gate electrostatics that allows for efficient switching of ultra-short organic channels. This affords room temperature conductance modulation by orders of magnitude for organic transistors that are only several molecules in length, with switching characteristics superior to similar devices with lithographically patterned metal electrodes. With nanotubes, covalent carbon-carbon bonds could be utilized to form contacts to molecular materials. The unique geometrical, physical, and chemical properties of carbon nanotube electrodes may lead to various interesting molecular devices.

    View details for DOI 10.1021/ja045900k

    View details for Web of Science ID 000224103900012

    View details for PubMedID 15382895

  • Surface chemistry and electrical properties of germanium nanowires JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Wang, D. W., Chang, Y. L., Wang, Q., Cao, J., Farmer, D. B., Gordon, R. G., Dai, H. J. 2004; 126 (37): 11602-11611

    Abstract

    Germanium nanowires (GeNWs) with p- and n-dopants were synthesized by chemical vapor deposition (CVD) and were used to construct complementary field-effect transistors (FETs). Electrical transport and X-ray photoelectron spectroscopy (XPS) data are correlated to glean the effects of Ge surface chemistry to the electrical characteristics of GeNWs. Large hysteresis due to water molecules strongly bound to GeO(2) on GeNWs is revealed. Different oxidation behavior and hysteresis characteristics and opposite band bending due to Fermi level pinning by interface states between Ge and surface oxides are observed for p- and n-type GeNWs. Vacuum annealing above 400 degrees C is used to remove surface oxides and eliminate hysteresis in GeNW FETs. High-kappa dielectric HfO(2) films grown on clean GeNW surfaces by atomic layer deposition (ALD) using an alkylamide precursor is effective in serving as the first layer of surface passivation. Lastly, the depletion length along the radial direction of nanowires is evaluated. The result suggests that surface effects could be dominant over the "bulk" properties of small diameter wires.

    View details for DOI 10.1021/ja047435x

    View details for Web of Science ID 000223921800046

    View details for PubMedID 15366907

  • Ten- to 50-nm-long quasi-ballistic carbon nanotube devices obtained without complex lithography PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Javey, A., Qi, P. F., Wang, Q., Dai, H. J. 2004; 101 (37): 13408-13410

    Abstract

    A simple method combining photolithography and shadow (or angle) evaporation is developed to fabricate single-walled carbon nanotube (SWCNT) devices with tube lengths of approximately 10-50 nm between metal contacts. Large numbers of such short devices are obtained without the need of complex tools such as electron beam lithography. Metallic SWCNTs with lengths of approximately 10 nm, near the mean free path of l(op) approximately 15 nm for optical phonon scattering, exhibit nearly ballistic transport at high biases and can carry unprecedented 100-microA currents per tube. Semiconducting SWCNT field-effect transistors with approximately 50-nm channel lengths are routinely produced to achieve quasi-ballistic operations for molecular transistors. The results demonstrate highly length-scaled and high-performance interconnects and transistors realized with SWCNTs.

    View details for DOI 10.1073/pnas.0404450101

    View details for Web of Science ID 000223917900004

    View details for PubMedID 15347810

  • Nanotube molecular transporters: Internalization of carbon nanotube-protein conjugates into mammalian cells JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Kam, N. W., Jessop, T. C., Wender, P. A., Dai, H. J. 2004; 126 (22): 6850-6851

    Abstract

    The interactions between various functionalized carbon nanotubes and several types of human cancer cells are explored. We have prepared modified nanotubes and have shown that these can be derivatized in a way that enables attachment of small molecules and of proteins, the latter through a novel noncovalent association. The functionalized carbon nanotubes enter nonadherent human cancer cells as well as adherent cell lines (CHO and 3T3) and by themselves are not toxic. While the fluoresceinated protein streptavidin (MW approximately 60 kD) by itself does not enter cells, it readily enters cells when complexed to a nanotube-biotin transporter and exhibits dose-dependent cytotoxicity. The uptake pathway is consistent with adsorption-mediated endocytosis. The use of carbon nanotubes as molecular transporters could be exploited for various cargos. The biocompatibility and unique physical, electrical, optical, and mechanical properties of nanotubes provide the basis for new classes of materials for drug, protein, and gene delivery applications.

    View details for DOI 10.1021/ja0486059

    View details for Web of Science ID 000221828200007

    View details for PubMedID 15174838

  • High-field quasiballistic transport in short carbon nanotubes PHYSICAL REVIEW LETTERS Javey, A., Guo, J., Paulsson, M., Wang, Q., Mann, D., Lundstrom, M., Dai, H. J. 2004; 92 (10)

    Abstract

    Single walled carbon nanotubes with Pd Ohmic contacts and lengths ranging from several microns down to 10 nm are investigated by electron transport experiments and theory. The mean-free path (MFP) for acoustic phonon scattering is estimated to be l(ap) approximately 300 nm, and that for optical phonon scattering is l(op) approximately 15 nm. Transport through very short (approximately 10 nm) nanotubes is free of significant acoustic and optical phonon scattering and thus ballistic and quasiballistic at the low- and high-bias voltage limits, respectively. High currents of up to 70 microA can flow through a short nanotube. Possible mechanisms for the eventual electrical breakdown of short nanotubes at high fields are discussed. The results presented here have important implications to high performance nanotube transistors and interconnects.

    View details for DOI 10.1103/PhysRevLett.92.106804

    View details for Web of Science ID 000220185600040

    View details for PubMedID 15089227

  • An investigation of the mechanisms of electronic sensing of protein adsorption on carbon nanotube devices JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Chen, R. J., Choi, H. C., Bangsaruntip, S., Yenilmez, E., Tang, X. W., Wang, Q., Chang, Y. L., Dai, H. J. 2004; 126 (5): 1563-1568

    Abstract

    It has been reported that protein adsorption on single-walled carbon nanotube field effect transistors (FETs) leads to appreciable changes in the electrical conductance of the devices, a phenomenon that can be exploited for label-free detection of biomolecules with a high potential for miniaturization. This work presents an elucidation of the electronic biosensing mechanisms with a newly developed microarray of nanotube "micromat" sensors. Chemical functionalization schemes are devised to block selected components of the devices from protein adsorption, self-assembled monolayers (SAMs) of methoxy(poly(ethylene glycol))thiol (mPEG-SH) on the metal electrodes (Au, Pd) and PEG-containing surfactants on the nanotubes. Extensive characterization reveals that electronic effects occurring at the metal-nanotube contacts due to protein adsorption constitute a more significant contribution to the electronic biosensing signal than adsorption solely along the exposed lengths of the nanotubes.

    View details for DOI 10.1021/ja038702m

    View details for Web of Science ID 000188834900054

    View details for PubMedID 14759216

  • Ballistic carbon nanotube field-effect transistors NATURE Javey, A., Guo, J., Wang, Q., Lundstrom, M., Dai, H. J. 2003; 424 (6949): 654-657

    Abstract

    A common feature of the single-walled carbon-nanotube field-effect transistors fabricated to date has been the presence of a Schottky barrier at the nanotube--metal junctions. These energy barriers severely limit transistor conductance in the 'ON' state, and reduce the current delivery capability--a key determinant of device performance. Here we show that contacting semiconducting single-walled nanotubes by palladium, a noble metal with high work function and good wetting interactions with nanotubes, greatly reduces or eliminates the barriers for transport through the valence band of nanotubes. In situ modification of the electrode work function by hydrogen is carried out to shed light on the nature of the contacts. With Pd contacts, the 'ON' states of semiconducting nanotubes can behave like ohmically contacted ballistic metallic tubes, exhibiting room-temperature conductance near the ballistic transport limit of 4e(2)/h (refs 4-6), high current-carrying capability (approximately 25 micro A per tube), and Fabry-Perot interferences at low temperatures. Under high voltage operation, the current saturation appears to be set by backscattering of the charge carriers by optical phonons. High-performance ballistic nanotube field-effect transistors with zero or slightly negative Schottky barriers are thus realized.

    View details for DOI 10.1038/nature01797

    View details for Web of Science ID 000184578800039

    View details for PubMedID 12904787

  • Noncovalent functionalization of carbon nanotubes for highly specific electronic biosensors PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Chen, R. J., Bangsaruntip, S., Drouvalakis, K. A., Kam, N. W., Shim, M., Li, Y. M., Kim, W., Utz, P. J., DAI, H. J. 2003; 100 (9): 4984-4989

    Abstract

    Novel nanomaterials for bioassay applications represent a rapidly progressing field of nanotechnology and nanobiotechnology. Here, we present an exploration of single-walled carbon nanotubes as a platform for investigating surface-protein and protein-protein binding and developing highly specific electronic biomolecule detectors. Nonspecific binding on nanotubes, a phenomenon found with a wide range of proteins, is overcome by immobilization of polyethylene oxide chains. A general approach is then advanced to enable the selective recognition and binding of target proteins by conjugation of their specific receptors to polyethylene oxide-functionalized nanotubes. This scheme, combined with the sensitivity of nanotube electronic devices, enables highly specific electronic sensors for detecting clinically important biomolecules such as antibodies associated with human autoimmune diseases.

    View details for DOI 10.1073/pnas.0837064100

    View details for Web of Science ID 000182612600006

    View details for PubMedID 12697899

  • Electromechanical properties of metallic, quasimetallic, and semiconducting carbon nanotubes under stretching PHYSICAL REVIEW LETTERS Cao, J., Wang, Q., Dai, H. J. 2003; 90 (15)

    Abstract

    An electromechanical system is constructed to explore the electrical properties of various types of suspended single-walled carbon nanotubes under the influence of tensile stretching. Small band-gap semiconducting (or quasimetallic) nanotubes exhibit the largest resistance changes and piezoresistive gauge factors ( approximately 600 to 1000) under axial strains. Metallic nanotubes exhibit much weaker but nonzero sensitivity. Comparison between experiments and theoretical predictions and potential applications of nanotube electromechanical systems for physical sensors (e.g., strain gauges, pressure sensors, etc.) are discussed.

    View details for DOI 10.1103/PhysRevLett.90.157601

    View details for Web of Science ID 000182320200049

    View details for PubMedID 12732069

  • Ring opening metathesis polymerization on non-covalently functionalized single-walled carbon nanotubes CHEMICAL COMMUNICATIONS Gomez, F. J., Chen, R. J., Wang, D. W., Waymouth, R. M., Dai, H. J. 2003: 190-191

    Abstract

    Norbornene polymerization has been initiated selectively on the surface of single-walled carbon nanotubes (SWNTs) via a specifically adsorbed pyrene-linked ROMP initiator, resulting in a homogeneous non-covalent poly(norbornene) coating.

    View details for DOI 10.1039/b211194b

    View details for Web of Science ID 000180249600008

    View details for PubMedID 12585385

  • High-kappa dielectrics for advanced carbon-nanotube transistors and logic gates NATURE MATERIALS Javey, A., Kim, H., Brink, M., Wang, Q., Ural, A., Guo, J., McIntyre, P., McEuen, P., Lundstrom, M., DAI, H. J. 2002; 1 (4): 241-246

    Abstract

    The integration of materials having a high dielectric constant (high-kappa) into carbon-nanotube transistors promises to push the performance limit for molecular electronics. Here, high-kappa (approximately 25) zirconium oxide thin-films (approximately 8 nm) are formed on top of individual single-walled carbon nanotubes by atomic-layer deposition and used as gate dielectrics for nanotube field-effect transistors. The p-type transistors exhibit subthreshold swings of S approximately 70 mV per decade, approaching the room-temperature theoretical limit for field-effect transistors. Key transistor performance parameters, transconductance and carrier mobility reach 6,000 S x m(-1) (12 microS per tube) and 3,000 cm2 x V(-1) x s(-1) respectively. N-type field-effect transistors obtained by annealing the devices in hydrogen exhibit S approximately 90 mV per decade. High voltage gains of up to 60 are obtained for complementary nanotube-based inverters. The atomic-layer deposition process affords gate insulators with high capacitance while being chemically benign to nanotubes, a key to the integration of advanced dielectrics into molecular electronics.

    View details for DOI 10.1038/nmat769

    View details for Web of Science ID 000181498800022

    View details for PubMedID 12618786

  • Carbon nanotubes: Synthesis, integration, and properties ACCOUNTS OF CHEMICAL RESEARCH DAI, H. J. 2002; 35 (12): 1035-1044

    Abstract

    Synthesis of carbon nanotubes by chemical vapor deposition over patterned catalyst arrays leads to nanotubes grown from specific sites on surfaces. The growth directions of the nanotubes can be controlled by van der Waals self-assembly forces and applied electric fields. The patterned growth approach is feasible with discrete catalytic nanoparticles and scalable on large wafers for massive arrays of novel nanowires. Controlled synthesis of nanotubes opens up exciting opportunities in nanoscience and nanotechnology, including electrical, mechanical, and electromechanical properties and devices, chemical functionalization, surface chemistry and photochemistry, molecular sensors, and interfacing with soft biological systems.

    View details for DOI 10.1021/ar0101640

    View details for Web of Science ID 000179918200006

    View details for PubMedID 12484791

  • Spontaneous reduction of metal ions on the sidewalls of carbon nanotubes JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Choi, H. C., Shim, M., Bangsaruntip, S., Dai, H. J. 2002; 124 (31): 9058-9059

    Abstract

    Nanotube/nanoparticle hybrid structures are prepared by forming Au and Pt nanoparticles on the sidewalls of single-walled carbon nanotubes. Reducing agent or catalyst-free electroless deposition, which purely utilizes the redox potential difference between Au3+, Pt2+, and the carbon nanotube, is the main driving force for this reaction. It is also shown that carbon nanotubes act as a template for wire-like metal structures. The successful formation of the hybrid structures is monitored by atomic force microscopy (AFM) and electrical measurements.

    View details for DOI 10.1021/ja026824t

    View details for Web of Science ID 000177209500027

    View details for PubMedID 12149003

  • Low-temperature synthesis of single-crystal germanium nanowires by chemical vapor deposition ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Wang, D. W., DAI, H. J. 2002; 41 (24): 4783-4786

    View details for Web of Science ID 000180051600048

    View details for PubMedID 12481357

  • Polymer functionalization for air-stable n-type carbon nanotube field-effect transistors JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Shim, M., Javey, A., Kam, N. W., DAI, H. J. 2001; 123 (46): 11512-11513

    View details for DOI 10.1021/ja0169670

    View details for Web of Science ID 000172240100037

    View details for PubMedID 11707143

  • Functionalized carbon nanotubes for molecular hydrogen sensors ADVANCED MATERIALS Kong, J., Chapline, M. G., DAI, H. J. 2001; 13 (18): 1384-1386
  • Quantum interference and ballistic transmission in nanotube electron waveguides PHYSICAL REVIEW LETTERS Kong, J., Yenilmez, E., Tombler, T. W., Kim, W., DAI, H. J., Laughlin, R. B., Liu, L., Jayanthi, C. S., Wu, S. Y. 2001; 87 (10)

    Abstract

    The electron transport properties of well-contacted individual single-walled carbon nanotubes are investigated in the ballistic regime. Phase coherent transport and electron interference manifest as conductance fluctuations as a function of Fermi energy. Resonance with standing waves in finite-length tubes and localized states due to imperfections are observed for various Fermi energies. Two units of quantum conductance 2G(0) = 4e(2)/h are measured for the first time, corresponding to the maximum conductance limit for ballistic transport in two channels of a nanotube.

    View details for DOI 10.1103/PhysRevLett.87.106801

    View details for Web of Science ID 000170901300030

    View details for PubMedID 11531494

  • Noncovalent sidewall functionalization of single-walled carbon nanotubes for protein immobilization JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Chen, R. J., Zhang, Y. G., Wang, D. W., DAI, H. J. 2001; 123 (16): 3838-3839

    View details for DOI 10.1021/ja010172b

    View details for Web of Science ID 000168442500032

    View details for PubMedID 11457124

  • Modulated chemical doping of individual carbon nanotubes SCIENCE Zhou, C. W., Kong, J., Yenilmez, E., DAI, H. J. 2000; 290 (5496): 1552-1555

    Abstract

    Modulation doping of a semiconducting single-walled carbon nanotube along its length leads to an intramolecular wire electronic device. The nanotube is doped n-type for half of its length and p-type for the other half. Electrostatic gating can tune the system into p-n junctions, causing it to exhibit rectifying characteristics or negative differential conductance. The system can also be tuned into n-type, exhibiting single-electron charging and negative differential conductance at low temperatures. The low-temperature behavior is manifested by a quantum dot formed by chemical inhomogeneity along the tube.

    View details for Web of Science ID 000165446200043

    View details for PubMedID 11090348

  • An enhanced CVD approach to extensive nanotube networks with directionality ADVANCED MATERIALS Franklin, N. R., DAI, H. J. 2000; 12 (12): 890-894
  • Controlling nanotube growth PHYSICS WORLD DAI, H. J. 2000; 13 (6): 43-47
  • Nanotube molecular wires as chemical sensors SCIENCE Kong, J., Franklin, N. R., Zhou, C. W., Chapline, M. G., Peng, S., Cho, K. J., DAI, H. J. 2000; 287 (5453): 622-625
  • Intrinsic electrical properties of individual single-walled carbon nanotubes with small band gaps Physical review letters Zhou, C., Kong, J., Dai, H. 2000; 84 (24): 5604-7

    Abstract

    Individual single-walled carbon nanotubes (SWNT) exhibiting small band gaps on the order of 10 meV are observed for the first time in electron transport measurements. Transport through the valence or conduction band of a small-gap semiconducting SWNT (SGS-SWNT) can be tuned by a nearby gate voltage. Intrinsic electrical properties of the Ohmically contacted SGS-SWNT are elucidated. An SGS-SWNT exhibits metal- or semiconductorlike characteristics depending on the Fermi level position in the band structure.

    View details for PubMedID 10991005

  • Reversible electromechanical characteristics of carbon nanotubes under local-probe manipulation Nature Tombler, T. W., Zhou, C., Alexseyev, L., Kong, J., Dai, H., Liu, L., Jayanthi, C. S., Tang, M., Wu, S. Y. 2000; 405 (6788): 769-72

    Abstract

    The effects of mechanical deformation on the electrical properties of carbon nanotubes are of interest given the practical potential of nanotubes in electromechanical devices, and they have been studied using both theoretical and experimental approaches. One recent experiment used the tip of an atomic force microscope (AFM) to manipulate multi-walled nanotubes, revealing that changes in the sample resistance were small unless the nanotubes fractured or the metal-tube contacts were perturbed. But it remains unclear how mechanical deformation affects the intrinsic electrical properties of nanotubes. Here we report an experimental and theoretical elucidation of the electromechanical characteristics of individual single-walled carbon nanotubes (SWNTs) under local-probe manipulation. We use AFM tips to deflect suspended SWNTs reversibly, without changing the contact resistance; in situ electrical measurements reveal that the conductance of an SWNT sample can be reduced by two orders of magnitude when deformed by an AFM tip. Our tight-binding simulations indicate that this effect is owing to the formation of local sp3 bonds caused by the mechanical pushing action of the tip.

    View details for PubMedID 10866192

  • Nanotube molecular wires as chemical sensors Science (New York, N.Y.) Kong, J., Franklin, N. R., Zhou, C., Chapline, M. G., Peng, S., Cho, K., Dai, H. 2000; 287 (5453): 622-5

    Abstract

    Chemical sensors based on individual single-walled carbon nanotubes (SWNTs) are demonstrated. Upon exposure to gaseous molecules such as NO(2) or NH(3), the electrical resistance of a semiconducting SWNT is found to dramatically increase or decrease. This serves as the basis for nanotube molecular sensors. The nanotube sensors exhibit a fast response and a substantially higher sensitivity than that of existing solid-state sensors at room temperature. Sensor reversibility is achieved by slow recovery under ambient conditions or by heating to high temperatures. The interactions between molecular species and SWNTs and the mechanisms of molecular sensing with nanotube molecular wires are investigated.

    View details for PubMedID 10649989

  • Directed growth of free-standingsingle-walled carbon nanotubes JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Cassell, A. M., Franklin, N. R., Tombler, T. W., Chan, E. M., Han, J., DAI, H. J. 1999; 121 (34): 7975-7976
  • Self-oriented regular arrays of carbon nanotubes and their field emission properties SCIENCE Fan, S. S., Chapline, M. G., Franklin, N. R., Tombler, T. W., Cassell, A. M., DAI, H. J. 1999; 283 (5401): 512-514
  • Self-oriented regular arrays of carbon nanotubes and their field emission properties Science (New York, N.Y.) Fan, S., Chapline, M. G., Franklin, N. R., Tombler, T. W., Cassell, A. M., Dai, H. 1999; 283 (5401): 512-4

    Abstract

    The synthesis of massive arrays of monodispersed carbon nanotubes that are self-oriented on patterned porous silicon and plain silicon substrates is reported. The approach involves chemical vapor deposition, catalytic particle size control by substrate design, nanotube positioning by patterning, and nanotube self-assembly for orientation. The mechanisms of nanotube growth and self-orientation are elucidated. The well-ordered nanotubes can be used as electron field emission arrays. Scaling up of the synthesis process should be entirely compatible with the existing semiconductor processes, and should allow the development of nanotube devices integrated into silicon technology.

    View details for PubMedID 9915692

  • Gate-Controlled Superconducting Proximity Effect in Carbon Nanotubes. Science (New York, N.Y.) Morpurgo, A. F., Kong, J., Marcus, C. M., Dai, H. 1999; 286 (5438): 263-265

    Abstract

    The superconducting proximity effect in single-walled carbon nanotubes connected to niobium electrodes was controlled with the use of nearby gates that tune the niobium-nanotube transparency. At 4.2 kelvin, when the transparency was tuned to be high, a dip in the low-bias differential resistance was observed, indicating a proximity effect mediated by Andreev reflection. When the transparency was tuned to be low, signatures of Andreev reflection disappeared and only tunneling conduction was observed. Below approximately 4 kelvin, a narrow peak in differential resistance around zero bias appeared superimposed on the Andreev dip, probably as a result of electron-electron interaction competing with the proximity effect.

    View details for PubMedID 10514364

  • Synthesis of individual single-walled carbon nanotubes on patterned silicon wafers NATURE Kong, J., Soh, H. T., Cassell, A. M., Quate, C. F., Dai, H. J. 1998; 395 (6705): 878-881