Nicholas Melosh

All Publications

• Cavity-Enhanced Raman Emission from a Single Color Center in a Solid. Physical review letters Sun, S., Zhang, J. L., Fischer, K. A., Burek, M. J., Dory, C., Lagoudakis, K. G., Tzeng, Y., Radulaski, M., Kelaita, Y., Safavi-Naeini, A., Shen, Z., Melosh, N. A., Chu, S., Loncar, M., Vuckovic, J. 2018; 121 (8): 083601

  Abstract

  We demonstrate cavity-enhanced Raman emission from a single atomic defect in a solid. Our platform is a single silicon-vacancy center in diamond coupled with a monolithic diamond photonic crystal cavity. The cavity enables an unprecedented frequency tuning range of the Raman emission (100GHz) that significantly exceeds the spectral inhomogeneity of silicon-vacancy centers in diamond nanostructures. We also show that the cavity selectively suppresses the phonon-induced spontaneous emission that degrades the efficiency of Raman photon generation. Our results pave the way towards photon-mediated many-body interactions between solid-state quantum emitters in a nanophotonic platform.

  View details for DOI 10.1103/PhysRevLett.121.083601

  View details for PubMedID 30192607

• Experimental measurement of the diamond nucleation landscape reveals classical and nonclassical features. Proceedings of the National Academy of Sciences of the United States of America Gebbie, M. A., Ishiwata, H., McQuade, P. J., Petrak, V., Taylor, A., Freiwald, C., Dahl, J. E., Carlson, R. M., Fokin, A. A., Schreiner, P. R., Shen, Z., Nesladek, M., Melosh, N. A. 2018

  Abstract

  Nucleation is a core scientific concept that describes the formation of new phases and materials. While classical nucleation theory is applied across wide-ranging fields, nucleation energy landscapes have never been directly measured at the atomic level, and experiments suggest that nucleation rates often greatly exceed the predictions of classical nucleation theory. Multistep nucleation via metastable states could explain unexpectedly rapid nucleation in many contexts, yet experimental energy landscapes supporting such mechanisms are scarce, particularly at nanoscale dimensions. In this work, we measured the nucleation energy landscape of diamond during chemical vapor deposition, using a series of diamondoid molecules as atomically defined protonuclei. We find that 26-carbon atom clusters, which do not contain a single bulk atom, are postcritical nuclei and measure the nucleation barrier to be more than four orders of magnitude smaller than prior bulk estimations. These data support both classical and nonclassical concepts for multistep nucleation and growth during the gas-phase synthesis of diamond and other semiconductors. More broadly, these measurements provide experimental evidence that agrees with recent conceptual proposals of multistep nucleation pathways with metastable molecular precursors in diverse processes, ranging from cloud formation to protein crystallization, and nanoparticle synthesis.

  View details for DOI 10.1073/pnas.1803654115

  View details for PubMedID 30068609

• Electronic and Ionic Materials for Neurointerfaces ADVANCED FUNCTIONAL MATERIALS Ferro, M. D., Melosh, N. A. 2018; 28 (12)

  View details for DOI 10.1002/adfm.201704335

  View details for Web of Science ID 000428347700021

• Sterically controlled mechanochemistry under hydrostatic pressure NATURE Yan, H., Yang, F., Pan, D., Lin, Y., Hohman, J., Solis-Ibarra, D., Li, F., Dahl, J. P., Carlson, R. K., Tkachenko, B. A., Fokin, A. A., Schreiner, P. R., Galli, G., Mao, W. L., Shen, Z., Melosh, N. A. 2018; 554 (7693): 505-+

  Abstract

  Mechanical stimuli can modify the energy landscape of chemical reactions and enable reaction pathways, offering a synthetic strategy that complements conventional chemistry. These mechanochemical mechanisms have been studied extensively in one-dimensional polymers under tensile stress using ring-opening and reorganization, polymer unzipping and disulfide reduction as model reactions. In these systems, the pulling force stretches chemical bonds, initiating the reaction. Additionally, it has been shown that forces orthogonal to the chemical bonds can alter the rate of bond dissociation. However, these bond activation mechanisms have not been possible under isotropic, compressive stress (that is, hydrostatic pressure). Here we show that mechanochemistry through isotropic compression is possible by molecularly engineering structures that can translate macroscopic isotropic stress into molecular-level anisotropic strain. We engineer molecules with mechanically heterogeneous components-a compressible ('soft') mechanophore and incompressible ('hard') ligands. In these 'molecular anvils', isotropic stress leads to relative motions of the rigid ligands, anisotropically deforming the compressible mechanophore and activating bonds. Conversely, rigid ligands in steric contact impede relative motion, blocking reactivity. We combine experiments and computations to demonstrate hydrostatic-pressure-driven redox reactions in metal-organic chalcogenides that incorporate molecular elements that have heterogeneous compressibility, in which bending of bond angles or shearing of adjacent chains activates the metal-chalcogen bonds, leading to the formation of the elemental metal. These results reveal an unexplored reaction mechanism and suggest possible strategies for high-specificity mechanosynthesis.

  View details for DOI 10.1038/nature25765

  View details for Web of Science ID 000425597400042

  View details for PubMedID 29469090

• Monochromatic Photocathodes from Graphene-Stabilized Diamondoids NANO LETTERS Yan, H., Narasimha, K. T., Denlinger, J., Li, F., Mo, S., Hohman, J., Dahl, J. P., Carlson, R. K., Tkachenko, B. A., Fokin, A. A., Schreiner, P. R., Hussain, Z., Shen, Z., Melosh, N. A. 2018; 18 (2): 1099–1103

  Abstract

  The monochromatic photoemission from diamondoid monolayers provides a new strategy to create electron sources with low energy dispersion and enables compact electron guns with high brightness and low beam emittance for aberration-free imaging, lithography, and accelerators. However, these potential applications are hindered by degradation of diamondoid monolayers under photon irradiation and electron bombardment. Here, we report a graphene-protected diamondoid monolayer photocathode with 4-fold enhancement of stability compared to the bare diamondoid counterpart. The single-layer graphene overcoating preserves the monochromaticity of the photoelectrons, showing 12.5 meV ful width at half-maximum distribution of kinetic energy. Importantly, the graphene coating effectively suppresses desorption of the diamondoid monolayer, enhancing its thermal stability by at least 100 K. Furthermore, by comparing the decay rate at different photon energies, we identify electron bombardment as the principle decay pathway for diamondoids under graphene protection. This provides a generic approach for stabilizing volatile species on photocathode surfaces, which could greatly improve performance of electron emitters.

  View details for DOI 10.1021/acs.nanolett.7b04645

  View details for Web of Science ID 000425559700063

  View details for PubMedID 29286670

• Strongly Cavity-Enhanced Spontaneous Emission from Silicon-Vacancy Centers in Diamond NANO LETTERS Zhang, J., Sun, S., Burek, M. J., Dory, C., Tzeng, Y., Fischer, K. A., Kelaita, Y., Lardakis, K. G., Radulaski, M., Shen, Z., Melosh, N. A., Chu, S., Loncar, M., Vuckovic, J. 2018; 18 (2): 1360–65

  Abstract

  Quantum emitters are an integral component for a broad range of quantum technologies, including quantum communication, quantum repeaters, and linear optical quantum computation. Solid-state color centers are promising candidates for scalable quantum optics due to their long coherence time and small inhomogeneous broadening. However, once excited, color centers often decay through phonon-assisted processes, limiting the efficiency of single-photon generation and photon-mediated entanglement generation. Herein, we demonstrate strong enhancement of spontaneous emission rate of a single silicon-vacancy center in diamond embedded within a monolithic optical cavity, reaching a regime in which the excited-state lifetime is dominated by spontaneous emission into the cavity mode. We observe 10-fold lifetime reduction and 42-fold enhancement in emission intensity when the cavity is tuned into resonance with the optical transition of a single silicon-vacancy center, corresponding to 90% of the excited-state energy decay occurring through spontaneous emission into the cavity mode. We also demonstrate the largest coupling strength (g/2π = 4.9 ± 0.3 GHz) and cooperativity (C = 1.4) to date for color-center-based cavity quantum electrodynamics systems, bringing the system closer to the strong coupling regime.

  View details for DOI 10.1021/acs.nanolett.7b05075

  View details for Web of Science ID 000425559700102

  View details for PubMedID 29377701

• Functionalisation of Detonation Nanodiamond for Monodispersed, Soluble DNA-Nanodiamond Conjugates Using Mixed Silane Bead-Assisted Sonication Disintegration SCIENTIFIC REPORTS Edgington, R., Spillane, K. M., Papageorgiou, G., Wray, W., Ishiwata, H., Labarca, M., Leal-Ortiz, S., Reid, G., Webb, M., Foord, J., Melosh, N., Schaefer, A. T. 2018; 8: 728

  Abstract

  Nanodiamonds have many attractive properties that make them suitable for a range of biological applications, but their practical use has been limited because nanodiamond conjugates tend to aggregate in solution during or after functionalisation. Here we demonstrate the production of DNA-detonation nanodiamond (DNA-DND) conjugates with high dispersion and solubility using an ultrasonic, mixed-silanization chemistry protocol based on the in situ Bead-Assisted Sonication Disintegration (BASD) silanization method. We use two silanes to achieve these properties: (1) 3-(trihydroxysilyl)propyl methylphosphonate (THPMP); a negatively charged silane that imparts high zeta potential and solubility in solution; and (2) (3-aminopropyl)triethoxysilane (APTES); a commonly used functional silane that contributes an amino group for subsequent bioconjugation. We target these amino groups for covalent conjugation to thiolated, single-stranded DNA oligomers using the heterobifunctional crosslinker sulfosuccinimidyl 4-(N-maleimidomethyl)cyclohexane-1-carboxylate (Sulfo-SMCC). The resulting DNA-DND conjugates are the smallest reported to date, as determined by Dynamic Light Scattering (DLS) and Atomic Force Microscopy (AFM). The functionalisation method we describe is versatile and can be used to produce a wide variety of soluble DND-biomolecule conjugates.

  View details for DOI 10.1038/s41598-017-18601-6

  View details for Web of Science ID 000422636400032

  View details for PubMedID 29335424

  View details for PubMedCentralID PMC5768878

• Roadmap on semiconductor-cell biointerfaces. Physical biology Tian, B., Xu, S., Rogers, J. A., Cestellos-Blanco, S., Yang, P., Carvalho-de-Souza, J. L., Bezanilla, F., Liu, J., Bao, Z., Hjort, M., Cao, Y., Melosh, N., Lanzani, G., Benfenati, F., Galli, G., Gygi, F., Kautz, R., Gorodetsky, A. A., Kim, S. S., Lu, T. K., Anikeeva, P., Cifra, M., Krivosudsky, O., Havelka, D., Jiang, Y. 2018; 15 (3): 031002

  Abstract

  This roadmap outlines the role semiconductor-based materials play in understanding the complex biophysical dynamics at multiple length scales, as well as the design and implementation of next-generation electronic, optoelectronic, and mechanical devices for biointerfaces. The roadmap emphasizes the advantages of semiconductor building blocks in interfacing, monitoring, and manipulating the activity of biological components, and discusses the possibility of using active semiconductor-cell interfaces for discovering new signaling processes in the biological world.

  View details for DOI 10.1088/1478-3975/aa9f34

  View details for PubMedID 29205173

• Cellular Differentiation of Human Monocytes Is Regulated by Time-Dependent Interleukin-4 Signaling and the Transcriptional Regulator NCOR2 IMMUNITY Sander, J., Schmidt, S. V., Cirovic, B., McGovern, N., Papantonopoulou, O., Hardt, A., Aschenbrenner, A. C., Kreer, C., Quast, T., Xu, A. M., Schmidleithner, L. M., Theis, H., Lan Do Thi Huong, Bin Sumatoh, H., Lauterbach, M. R., Schulte-Schrepping, J., Guenther, P., Xue, J., Bassler, K., Ulas, T., Klee, K., Katzmarski, N., Herresthal, S., Krebs, W., Martin, B., Latz, E., Haendler, K., Kraut, M., Kolanus, W., Beyer, M., Falk, C. S., Wiegmann, B., Burgdorf, S., Melosh, N. A., Newell, E. W., Ginhoux, F., Schlitzer, A., Schultze, J. L. 2017; 47 (6): 1051-+

  Abstract

  Human in vitro generated monocyte-derived dendritic cells (moDCs) and macrophages are used clinically, e.g., to induce immunity against cancer. However, their physiological counterparts, ontogeny, transcriptional regulation, and heterogeneity remains largely unknown, hampering their clinical use. High-dimensional techniques were used to elucidate transcriptional, phenotypic, and functional differences between human in vivo and in vitro generated mononuclear phagocytes to facilitate their full potential in the clinic. We demonstrate that monocytes differentiated by macrophage colony-stimulating factor (M-CSF) or granulocyte macrophage colony-stimulating factor (GM-CSF) resembled in vivo inflammatory macrophages, while moDCs resembled in vivo inflammatory DCs. Moreover, differentiated monocytes presented with profound transcriptomic, phenotypic, and functional differences. Monocytes integrated GM-CSF and IL-4 stimulation combinatorically and temporally, resulting in a mode- and time-dependent differentiation relying on NCOR2. Finally, moDCs are phenotypically heterogeneous and therefore necessitate the use of high-dimensional phenotyping to open new possibilities for better clinical tailoring of these cellular therapies.

  View details for DOI 10.1016/j.immuni.2017.11.024

  View details for Web of Science ID 000418486500011

  View details for PubMedID 29262348

  View details for PubMedCentralID PMC5772172

• Temperature-dependent optical properties of titanium nitride APPLIED PHYSICS LETTERS Briggs, J. A., Naik, G. V., Zhao, Y., Petach, T. A., Sahasrabuddhe, K., Goldhaber-Gordon, D., Melosh, N. A., Dionne, J. A. 2017; 110 (10)

  View details for DOI 10.1063/1.4977840

  View details for Web of Science ID 000397871800011

• Hybrid metal-organic chalcogenide nanowires with electrically conductive inorganic core through diamondoid-directed assembly. Nature materials Yan, H., Hohman, J. N., Li, F. H., Jia, C., Solis-Ibarra, D., Wu, B., Dahl, J. E., Carlson, R. M., Tkachenko, B. A., Fokin, A. A., Schreiner, P. R., Vailionis, A., Kim, T. R., Devereaux, T. P., Shen, Z., Melosh, N. A. 2017; 16 (3): 349-355

  Abstract

  Controlling inorganic structure and dimensionality through structure-directing agents is a versatile approach for new materials synthesis that has been used extensively for metal-organic frameworks and coordination polymers. However, the lack of 'solid' inorganic cores requires charge transport through single-atom chains and/or organic groups, limiting their electronic properties. Here, we report that strongly interacting diamondoid structure-directing agents guide the growth of hybrid metal-organic chalcogenide nanowires with solid inorganic cores having three-atom cross-sections, representing the smallest possible nanowires. The strong van der Waals attraction between diamondoids overcomes steric repulsion leading to a cis configuration at the active growth front, enabling face-on addition of precursors for nanowire elongation. These nanowires have band-like electronic properties, low effective carrier masses and three orders-of-magnitude conductivity modulation by hole doping. This discovery highlights a previously unexplored regime of structure-directing agents compared with traditional surfactant, block copolymer or metal-organic framework linkers.

  View details for DOI 10.1038/nmat4823

  View details for PubMedID 28024157

• Nondestructive nanostraw intracellular sampling for longitudinal cell monitoring. Proceedings of the National Academy of Sciences of the United States of America Cao, Y., Hjort, M., Chen, H., Birey, F., Leal-Ortiz, S. A., Han, C. M., Santiago, J. G., Pasca, S. P., Wu, J. C., Melosh, N. A. 2017

  Abstract

  Here, we report a method for time-resolved, longitudinal extraction and quantitative measurement of intracellular proteins and mRNA from a variety of cell types. Cytosolic contents were repeatedly sampled from the same cell or population of cells for more than 5 d through a cell-culture substrate, incorporating hollow 150-nm-diameter nanostraws (NS) within a defined sampling region. Once extracted, the cellular contents were analyzed with conventional methods, including fluorescence, enzymatic assays (ELISA), and quantitative real-time PCR. This process was nondestructive with >95% cell viability after sampling, enabling long-term analysis. It is important to note that the measured quantities from the cell extract were found to constitute a statistically significant representation of the actual contents within the cells. Of 48 mRNA sequences analyzed from a population of cardiomyocytes derived from human induced pluripotent stem cells (hiPSC-CMs), 41 were accurately quantified. The NS platform samples from a select subpopulation of cells within a larger culture, allowing native cell-to-cell contact and communication even during vigorous activity such as cardiomyocyte beating. This platform was applied both to cell lines and to primary cells, including CHO cells, hiPSC-CMs, and human astrocytes derived in 3D cortical spheroids. By tracking the same cell or group of cells over time, this method offers an avenue to understand dynamic cell behavior, including processes such as induced pluripotency and differentiation.

  View details for DOI 10.1073/pnas.1615375114

  View details for PubMedID 28223521

• Vertical-Substrate MPCVD Epitaxial Nanodiamond Growth. Nano letters Tzeng, Y., Zhang, J. L., Lu, H., Ishiwata, H., Dahl, J., Carlson, R. M., Yan, H., Schreiner, P. R., Vuckovic, J., Shen, Z., Melosh, N., Chu, S. 2017

  Abstract

  Color center-containing nanodiamonds have many applications in quantum technologies and biology. Diamondoids, molecular-sized diamonds have been used as seeds in chemical vapor deposition (CVD) growth. However, optimizing growth conditions to produce high crystal quality nanodiamonds with color centers requires varying growth conditions that often leads to ad-hoc and time-consuming, one-at-a-time testing of reaction conditions. In order to rapidly explore parameter space, we developed a microwave plasma CVD technique using a vertical, rather than horizontally oriented stage-substrate geometry. With this configuration, temperature, plasma density, and atomic hydrogen density vary continuously along the vertical axis of the substrate. This variation allowed rapid identification of growth parameters that yield single crystal diamonds down to 10 nm in size and 75 nm diameter optically active center silicon-vacancy (Si-V) nanoparticles. Furthermore, this method may provide a means of incorporating a wide variety of dopants in nanodiamonds without ion irradiation damage.

  View details for DOI 10.1021/acs.nanolett.6b04543

  View details for PubMedID 28182433

• Back-gated graphene anode for more efficient thermionic energy converters NANO ENERGY Yuan, H., Riley, D. C., Shen, Z., Pianetta, P. A., Melosh, N. A., Howe, R. T. 2017; 32: 67-72

  View details for DOI 10.1016/j.nanoen.2016.12.027

  View details for Web of Science ID 000397003700009

• Direct Intracellular Delivery of Cell Impermeable Probes of Protein Glycosylation Using Nanostraws. Chembiochem Xu, A. M., Wang, D. S., Shieh, P., Cao, Y., Melosh, N. 2017

  Abstract

  Bioorthogonal chemistry is an effective tool for elucidating metabolic pathways and measuring cellular activity, yet its use is currently limited by the difficulty of getting probes past the cell membrane and into the cytoplasm, especially if more complex probes are desired. Here we present a simple and minimally perturbative technique to deliver functional probes of glycosylation into cells by using a nanostructured "nanostraw" delivery system. Nanostraws provide direct intracellular access to cells through fluid conduits that remain small enough to minimize cell perturbation. First, we demonstrate that our platform can deliver an unmodified azidosugar, N-azidoacetylmannosamine, into cells with similar effectiveness to a chemical modification strategy (peracetylation). We then show that the nanostraw platform enables direct delivery of an azidosugar modified with a charged uridine diphosphate group (UDP) that prevents intracellular penetration, thereby bypassing multiple enzymatic processing steps. By effectively removing the requirement for cell permeability from the probe, the nanostraws expand the toolbox of bioorthogonal probes that can be used to study biological processes on a single, easy-to-use platform.

  View details for DOI 10.1002/cbic.201600689

  View details for PubMedID 28130882

• Complete Coherent Control of Silicon-Vacancies in Diamond Nanopillars Containing Single Defect Centers Zhang, J., Lagoudakis, K. G., Tzeng, Y., Dory, C., Radulaski, M., Kelaita, Y., Fischer, K. A., Shen, Z., Melosh, N. A., Chu, S., Vuckovic, J., IEEE IEEE. 2017

  View details for Web of Science ID 000427296200411

• Electronic devices: Nanoparticles make salty circuits. Nature nanotechnology Yan, H., Melosh, N. 2016; 11 (7): 579-580

  View details for DOI 10.1038/nnano.2016.46

  View details for PubMedID 26974955

• Fabrication of Sealed Nanostraw Microdevices for Oral Drug Delivery ACS NANO Fox, C. B., Cao, Y., Nemeth, C. L., Chirra, H. D., Chevalier, R. W., Xu, A. M., Melosh, N. A., Desai, T. A. 2016; 10 (6): 5873-5881

  Abstract

  The oral route is preferred for systemic drug administration and provides direct access to diseased tissue of the gastrointestinal (GI) tract. However, many drugs have poor absorption upon oral administration due to damaging enzymatic and pH conditions, mucus and cellular permeation barriers, and limited time for drug dissolution. To overcome these limitations and enhance oral drug absorption, micron-scale devices with planar, asymmetric geometries, termed microdevices, have been designed to adhere to the lining of the GI tract and release drug at high concentrations directly toward GI epithelium. Here we seal microdevices with nanostraw membranes-porous nanostructured biomolecule delivery substrates-to enhance the properties of these devices. We demonstrate that the nanostraws facilitate facile drug loading and tunable drug release, limit the influx of external molecules into the sealed drug reservoir, and increase the adhesion of devices to epithelial tissue. These findings highlight the potential of nanostraw microdevices to enhance the oral absorption of a wide range of therapeutics by binding to the lining of the GI tract, providing prolonged and proximal drug release, and reducing the exposure of their payload to drug-degrading biomolecules.

  View details for DOI 10.1021/acsnano.6b00809

  View details for Web of Science ID 000378973700030

  View details for PubMedID 27268699

• Ultralow effective work function surfaces using diamondoid monolayers. Nature nanotechnology Narasimha, K. T., Ge, C., Fabbri, J. D., Clay, W., Tkachenko, B. A., Fokin, A. A., Schreiner, P. R., Dahl, J. E., Carlson, R. M., Shen, Z. X., Melosh, N. A. 2016; 11 (3): 267-272

  Abstract

  Electron emission is critical for a host of modern fabrication and analysis applications including mass spectrometry, electron imaging and nanopatterning. Here, we report that monolayers of diamondoids effectively confer dramatically enhanced field emission properties to metal surfaces. We attribute the improved emission to a significant reduction of the work function rather than a geometric enhancement. This effect depends on the particular diamondoid isomer, with [121]tetramantane-2-thiol reducing gold's work function from ∼5.1 eV to 1.60 ± 0.3 eV, corresponding to an increase in current by a factor of over 13,000. This reduction in work function is the largest reported for any organic species and also the largest for any air-stable compound. This effect was not observed for sp(3)-hybridized alkanes, nor for smaller diamondoid molecules. The magnitude of the enhancement, molecule specificity and elimination of gold metal rearrangement precludes geometric factors as the dominant contribution. Instead, we attribute this effect to the stable radical cation of diamondoids. Our computed enhancement due to a positively charged radical cation was in agreement with the measured work functions to within ±0.3 eV, suggesting a new paradigm for low-work-function coatings based on the design of nanoparticles with stable radical cations.

  View details for DOI 10.1038/nnano.2015.277

  View details for PubMedID 26641529

• Hybrid Group IV Nanophotonic Structures Incorporating Diamond Silicon-Vacancy Color Centers NANO LETTERS Zhang, J. L., Ishiwata, H., Babinec, T. M., Radulaski, M., Mueller, K., Lagoudakis, K. G., Dory, C., Dahl, J., Edgington, R., Souliere, V., Ferro, G., Fokin, A. A., Schreiner, P. R., Shen, Z., Melosh, N. A., Vuckovic, J. 2016; 16 (1): 212-217

  Abstract

  We demonstrate a new approach for engineering group IV semiconductor-based quantum photonic structures containing negatively charged silicon-vacancy (SiV(-)) color centers in diamond as quantum emitters. Hybrid diamond-SiC structures are realized by combining the growth of nano- and microdiamonds on silicon carbide (3C or 4H polytype) substrates, with the subsequent use of these diamond crystals as a hard mask for pattern transfer. SiV(-) color centers are incorporated in diamond during its synthesis from molecular diamond seeds (diamondoids), with no need for ion-implantation or annealing. We show that the same growth technique can be used to grow a diamond layer controllably doped with SiV(-) on top of a high purity bulk diamond, in which we subsequently fabricate nanopillar arrays containing high quality SiV(-) centers. Scanning confocal photoluminescence measurements reveal optically active SiV(-) lines both at room temperature and low temperature (5 K) from all fabricated structures, and, in particular, very narrow line widths and small inhomogeneous broadening of SiV(-) lines from all-diamond nanopillar arrays, which is a critical requirement for quantum computation. At low temperatures (5 K) we observe in these structures the signature typical of SiV(-) centers in bulk diamond, consistent with a double lambda. These results indicate that high quality color centers can be incorporated into nanophotonic structures synthetically with properties equivalent to those in bulk diamond, thereby opening opportunities for applications in classical and quantum information processing.

  View details for DOI 10.1021/acs.nanolett.5b03515

  View details for Web of Science ID 000368322700034

• Temporally resolved direct delivery of second messengers into cells using nanostraws LAB ON A CHIP Xu, A. M., Kim, S. A., Wang, D. S., Aalipour, A., Melosh, N. A. 2016; 16 (13): 2434-2439

  Abstract

  Second messengers are biomolecules with the critical role of conveying information to intracellular targets. They are typically membrane-impermeable and only enter cells through tightly regulated transporters. Current methods for manipulating second messengers in cells require preparation of modified cell lines or significant disruptions in cell function, especially at the cell membrane. Here we demonstrate that 100 nm diameter 'nanostraws' penetrate the cell membrane to directly modulate second messenger concentrations within cells. Nanostraws are hollow vertical nanowires that provide a fluidic conduit into cells to allow time-resolved delivery of the signaling ion Ca(2+) without chemical permeabilization or genetic modification, minimizing cell perturbation. By integrating the nanostraw platform into a microfluidic device, we demonstrate coordinated delivery of Ca(2+) ions into hundreds of cells at the time scale of several seconds with the ability to deliver complex signal patterns, such as oscillations over time. The diffusive nature of nanostraw delivery gives the platform unique versatility, opening the possibility for time-resolved delivery of any freely diffusing molecules.

  View details for DOI 10.1039/c6lc00463f

  View details for Web of Science ID 000378941700008

  View details for PubMedID 27292263

• Significantly enhanced photocurrent for water oxidation in monolithic Mo:BiVO4/SnO2/Si by thermally increasing the minority carrier diffusion length ENERGY & ENVIRONMENTAL SCIENCE Zhang, L., Ye, X., Boloor, M., Poletayev, A., Melosh, N. A., Chueh, W. C. 2016; 9 (6): 2044-2052

  View details for DOI 10.1039/c6ee00036c

  View details for Web of Science ID 000378244200013

• Determining the Time Window for Dynamic Nanowire Cell Penetration Processes ACS NANO Xie, X., Aalipour, A., Gupta, S. V., Melosh, N. A. 2015; 9 (12): 11667-11677

  View details for DOI 10.1021/acsnano.5b05498

  View details for Web of Science ID 000367280100016

• Engineering Ultra-Low Work Function of Graphene NANO LETTERS Yuan, H., Chang, S., Bargatin, I., Wang, N. C., Riley, D. C., Wang, H., Schwede, J. W., Provine, J., Pop, E., Shen, Z., Pianetta, P. A., Melosh, N. A., Howe, R. T. 2015; 15 (10): 6475-6480

  Abstract

  Low work function materials are critical for energy conversion and electron emission applications. Here, we demonstrate for the first time that an ultralow work function graphene is achieved by combining electrostatic gating with a Cs/O surface coating. A simple device is built from large-area monolayer graphene grown by chemical vapor deposition, transferred onto 20 nm HfO2 on Si, enabling high electric fields capacitive charge accumulation in the graphene. We first observed over 0.7 eV work function change due to electrostatic gating as measured by scanning Kelvin probe force microscopy and confirmed by conductivity measurements. The deposition of Cs/O further reduced the work function, as measured by photoemission in an ultrahigh vacuum environment, which reaches nearly 1 eV, the lowest reported to date for a conductive, nondiamond material.

  View details for DOI 10.1021/acs.nanolett.5b01916

  View details for Web of Science ID 000363003100028

  View details for PubMedID 26401728

• Nanotechnology and neurophysiology CURRENT OPINION IN NEUROBIOLOGY Angle, M. R., Cui, B., Melosh, N. A. 2015; 32: 132-140

  View details for DOI 10.1016/j.conb.2015.03.014

  View details for Web of Science ID 000356198900018

• Nanotechnology and neurophysiology. Current opinion in neurobiology Angle, M. R., Cui, B., Melosh, N. A. 2015; 32: 132-140

  Abstract

  Neuroscience would be revolutionized by a technique to measure intracellular electrical potentials that would not disrupt cellular physiology and could be massively parallelized. Though such a technology does not yet exist, the technical hurdles for fabricating minimally disruptive, solid-state electrical probes have arguably been overcome in the field of nanotechnology. Nanoscale devices can be patterned with features on the same length scale as biological components, and several groups have demonstrated that nanoscale electrical probes can measure the transmembrane potential of electrogenic cells. Developing these nascent technologies into robust intracellular recording tools will now require a better understanding of device-cell interactions, especially the membrane-inorganic interface. Here we review the state-of-the art in nanobioelectronics, emphasizing the characterization and design of stable interfaces between nanoscale devices and cells.

  View details for DOI 10.1016/j.conb.2015.03.014

  View details for PubMedID 25889532

• Physical properties of materials derived from diamondoid molecules. Reports on progress in physics. Physical Society (Great Britain) CLAY, W. A., Dahl, J. E., Carlson, R. M., Melosh, N. A., Shen, Z. 2015; 78 (1): 016501-?

  Abstract

  Diamondoids are small hydrocarbon molecules which have the same rigid cage structure as bulk diamond. They can be considered the smallest nanoparticles of diamond. They exhibit a mixture of properties inherited from bulk cubic diamond as well as a number of unique properties related to their size and structure. Diamondoids with different sizes and shapes can be separated and purified, enabling detailed studies of the effects of size and structure on the diamondoids' properties and also allowing the creation of chemically functionalized diamondoids which can be used to create new materials. Most notable among these new materials are self-assembled monolayers of diamondoid-thiols, which exhibit a number of unique electron emission properties.

  View details for DOI 10.1088/0034-4885/78/1/016501

  View details for PubMedID 25551840

• Thermally-enhanced minority carrier collection in hematite during photoelectrochemical water and sulfite oxidation JOURNAL OF MATERIALS CHEMISTRY A Ye, X., Yang, J., Boloor, M., Melosh, N. A., Chueh, W. C. 2015; 3 (20): 10801-10810

  View details for DOI 10.1039/c5ta02108a

  View details for Web of Science ID 000354395400024

• Fabrication of sub-cell size "spiky'' nanoparticles and their interfaces with biological cells JOURNAL OF MATERIALS CHEMISTRY B Xie, X., Melosh, N. A. 2015; 3 (26): 5155-5160

  View details for DOI 10.1039/c5tb00452g

  View details for Web of Science ID 000356964700003

• Membrane indentation triggers clathrin lattice reorganization and fluidization SOFT MATTER Cordella, N., Lampo, T. J., Melosh, N., Spakowitz, A. J. 2015; 11 (3): 439-448

  View details for DOI 10.1039/c4sm01650e

  View details for Web of Science ID 000346911600002

• Physical properties of materials derived from diamondoid molecules REPORTS ON PROGRESS IN PHYSICS Clay, W. A., Dahl, J. E., Carlson, R. M., Melosh, N. A., Shen, Z. 2015; 78 (1)

  View details for DOI 10.1088/0034-4885/78/1/016501

  View details for Web of Science ID 000348760600003

  View details for PubMedID 25551840

• Membrane indentation triggers clathrin lattice reorganization and fluidization. Soft matter Cordella, N., Lampo, T. J., Melosh, N., Spakowitz, A. J. 2014; 11 (3): 439-448

  Abstract

  Clathrin-mediated endocytosis involves the coordinated assembly of clathrin cages around membrane indentations, necessitating fluid-like reorganization followed by solid-like stabilization. This apparent duality in clathrin's in vivo behavior provides some indication that the physical interactions between clathrin triskelia and the membrane effect a local response that triggers fluid-solid transformations within the clathrin lattice. We develop a computational model to study the response of clathrin protein lattices to spherical deformations of the underlying flexible membrane. These deformations are similar to the shapes assumed during intracellular trafficking of nanoparticles. Through Monte Carlo simulations of clathrin-on-membrane systems, we observe that these membrane indentations give rise to a greater than normal defect density within the overlaid clathrin lattice. In many cases, the bulk surrounding lattice remains in a crystalline phase, and the extra defects are localized to the regions of large curvature. This can be explained by the fact that the in-plane elastic stress in the clathrin lattice are reduced by coupling defects to highly curved regions. The presence of defects brought about by indentation can result in the fluidization of a lattice that would otherwise be crystalline, resulting in an indentation-driven, defect-mediated phase transition. Altering subunit elasticity or membrane properties is shown to drive a similar transition, and we present phase diagrams that map out the combined effects of these parameters on clathrin lattice properties.

  View details for DOI 10.1039/c4sm01650e

  View details for PubMedID 25412023

• Penetration of Cell Membranes and Synthetic Lipid Bilayers by Nanoprobes BIOPHYSICAL JOURNAL Angle, M. R., Wang, A., Thomas, A., Schaefer, A. T., Melosh, N. A. 2014; 107 (9): 2091-2100

  Abstract

  Nanoscale devices have been proposed as tools for measuring and controlling intracellular activity by providing electrical and/or chemical access to the cytosol. Unfortunately, nanostructures with diameters of 50-500 nm do not readily penetrate the cell membrane, and rationally optimizing nanoprobes for cell penetration requires real-time characterization methods that are capable of following the process of membrane penetration with nanometer resolution. Although extensive work has examined the rupture of supported synthetic lipid bilayers, little is known about the applicability of these model systems to living cell membranes with complex lipid compositions, cytoskeletal attachment, and membrane proteins. Here, we describe atomic force microscopy (AFM) membrane penetration experiments in two parallel systems: live HEK293 cells and stacks of synthetic lipid bilayers. By using the same probes in both systems, we were able to clearly identify membrane penetration in synthetic bilayers and compare these events with putative membrane penetration events in cells. We examined membrane penetration forces for three tip geometries and 18 chemical modifications of the probe surface, and in all cases the median forces required to penetrate cellular and synthetic lipid bilayers with nanoprobes were greater than 1 nN. The penetration force was sensitive to the probe's sharpness, but not its surface chemistry, and the force did not depend on cell surface or cytoskeletal properties, with cells and lipid stacks yielding similar forces. This systematic assessment of penetration under various mechanical and chemical conditions provides insights into nanoprobe-cell interactions and informs the design of future intracellular nanoprobes.

  View details for DOI 10.1016/j.bpj.2014.09.023

  View details for Web of Science ID 000344232500011

  View details for PubMedCentralID PMC4223211

• Plasma Membrane and Actin Cytoskeleton as Synergistic Barriers to Nanowire Cell Penetration LANGMUIR Aalipour, A., Xu, A. M., Leal-Ortiz, S., Garner, C. C., Melosh, N. A. 2014; 30 (41): 12362-12367

  View details for DOI 10.1021/la502273f

  View details for Web of Science ID 000343638800032

• Microfabricated Thermally Isolated Low Work-Function Emitter JOURNAL OF MICROELECTROMECHANICAL SYSTEMS Lee, J., Bargatin, I., Vancil, B. K., Gwinn, T. O., Maboudian, R., Melosh, N. A., Howe, R. T. 2014; 23 (5): 1182-1187

  View details for DOI 10.1109/JMEMS.2014.2307882

  View details for Web of Science ID 000343318500019

• Rheology and simulation of 2-dimensional clathrin protein network assembly. Soft matter VanDersarl, J. J., Mehraeen, S., Schoen, A. P., Heilshorn, S. C., Spakowitz, A. J., Melosh, N. A. 2014; 10 (33): 6219-6227

  Abstract

  Clathrin is a three-legged protein complex that assembles into lattice structures on the cell membrane and transforms into fullerene-like cages during endocytosis. This dynamic structural flexibility makes clathrin an attractive building block for guided assembly. The assembly dynamics and the mechanical properties of clathrin protein lattices are studied using rheological measurements and theoretical modelling in an effort to better understand two dynamic processes: protein adsorption to the interface and assembly into a network. We find that percolation models for protein network formation are insufficient to describe clathrin network formation, but with Monte Carlo simulations we can describe the dynamics of network formation very well. Insights from this work can be used to design new bio-inspired nano-assembly systems.

  View details for DOI 10.1039/c4sm00025k

  View details for PubMedID 25012232

• Rough-smooth-rough dynamic interface growth in supported lipid bilayers PHYSICAL REVIEW E Verma, P., Mager, M. D., Melosh, N. A. 2014; 89 (1)

  Abstract

  The role of lipid bilayer viscoelasticity and the substrate-bilayer interactions on the spreading behavior of supported phospholipid bilayer membranes is studied using fluorescence microscopy. Unlike the monotonic roughening observed on silica or in other dynamic interface growth systems, a unique rough-smooth-rough (RSR) interface transition occurred on chromium oxide with a roughness exponent of 0.45 ± 0.04. This RSR transition is attributed to the elasticity of the lipid bilayer which is initially under compression due to surface interactions, and is well approximated by adding an elastic term to the quenched noise Edwards-Wilkinson equation. A phase diagram depicting the conditions necessary to observe RSR transitions in dynamic interface systems is derived, revealing the classes of dynamically evolving systems is broader than previously thought, and the viscoelastic nature of the lipid bilayer may play a role in supported membrane behavior.

  View details for DOI 10.1103/PhysRevE.89.012404

  View details for Web of Science ID 000332162500012

  View details for PubMedID 24580234

• Quantification of nanowire penetration into living cells. Nature communications Xu, A. M., Aalipour, A., Leal-Ortiz, S., Mekhdjian, A. H., Xie, X., Dunn, A. R., Garner, C. C., Melosh, N. A. 2014; 5: 3613-?

  View details for DOI 10.1038/ncomms4613

  View details for PubMedID 24710350

• Mechanical Model of Vertical Nanowire Cell Penetration NANO LETTERS Xie, X., Xu, A. M., Angle, M. R., Tayebi, N., Verma, P., Melosh, N. A. 2013; 13 (12): 6002-6008

  Abstract

  Direct access into cells' interiors is essential for biomolecular delivery, gene transfection, and electrical recordings yet is challenging due to the cell membrane barrier. Recently, molecular delivery using vertical nanowires (NWs) has been demonstrated for introducing biomolecules into a large number of cells in parallel. However, the microscopic understanding of how and when the nanowires penetrate cell membranes is still lacking, and the degree to which actual membrane penetration occurs is controversial. Here we present results from a mechanical continuum model of elastic cell membrane penetration through two mechanisms, namely through "impaling" as cells land onto a bed of nanowires, and through "adhesion-mediated" penetration, which occurs as cells spread on the substrate and generate adhesion force. Our results reveal that penetration is much more effective through the adhesion mechanism, with NW geometry and cell stiffness being critically important. Stiffer cells have higher penetration efficiency, but are more sensitive to NW geometry. These results provide a guide to designing nanowires for applications in cell membrane penetration.

  View details for DOI 10.1021/nl403201a

  View details for Web of Science ID 000328439200039

  View details for PubMedID 24237230

• A semiconductor/mixed ion and electron conductor heterojunction for elevated-temperature water splitting. Physical chemistry chemical physics Ye, X., Melas-Kyriazi, J., Feng, Z. A., Melosh, N. A., Chueh, W. C. 2013; 15 (37): 15459-15469

  Abstract

  Photoelectrochemical cells (PECs) have been studied extensively for dissociating water into hydrogen and oxygen. Key bottlenecks for achieving high solar-to-hydrogen efficiency in PECs include increasing solar spectrum utilization, surmounting overpotential losses, and aligning the absorber/electrochemical redox levels. We propose a new class of solid-state PECs based on mixed ionic and electronic conducting (MIEC) oxides that operates at temperatures significantly above ambient and utilizes both the light and thermal energy available from concentrated sunlight to dissociate water vapor. Unlike thermochemical and hybrid photo-thermochemical water-splitting routes, the elevated-temperature PEC is a single-step approach operating isothermally. At the heart of the solid-state PEC is a semiconductor light absorber coated with a thin MIEC layer for improved catalytic activity, electrochemical stability, and ionic conduction. The MIEC, placed between the gas phase and the semiconductor light absorber, provides a facile path for minority carriers to reach the water vapor as well as a path for the ionic carriers to reach the solid electrolyte. Elevated temperature operation allows reasonable band misalignments at the interfaces to be overcome, reduces the required overpotential, and facilitates rapid product diffusion away from the surface. In this work, we simulate the behavior of an oxygen-ion-conducting photocathode in 1-D. Using the detailed-balance approach, in conjunction with recombination and electrochemical reaction rates, the practical efficiency is calculated as a function of temperature, solar flux, and select material properties. For a non-degenerate light absorber with a 2.0 eV band-gap and an uphill band offset of 0.3 eV, an efficiency of 17% and 11% is predicted at 723 and 873 K, respectively.

  View details for DOI 10.1039/c3cp52536h

  View details for PubMedID 23939203

• Covalent attachment of diamondoid phosphonic Acid dichlorides to tungsten oxide surfaces. Langmuir Li, F. H., Fabbri, J. D., Yurchenko, R. I., Mileshkin, A. N., Hohman, J. N., Yan, H., Yuan, H., Tran, I. C., Willey, T. M., Bagge-Hansen, M., Dahl, J. E., Carlson, R. M., Fokin, A. A., Schreiner, P. R., Shen, Z., Melosh, N. A. 2013; 29 (31): 9790-9797

  Abstract

  Diamondoids (nanometer-sized diamond-like hydrocarbons) are a novel class of carbon nanomaterials that exhibit negative electron affinity (NEA) and strong electron-phonon scattering. Surface-bound diamondoid monolayers exhibit monochromatic photoemission, a unique property that makes them ideal electron sources for electron-beam lithography and high-resolution electron microscopy. However, these applications are limited by the stability of the chemical bonding of diamondoids on surfaces. Here we demonstrate the stable covalent attachment of diamantane phosphonic dichloride on tungsten/tungsten oxide surfaces. X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared (FTIR) spectroscopy revealed that diamondoid-functionalized tungsten oxide films were stable up to 300-350 °C, a substantial improvement over conventional diamondoid thiolate monolayers on gold, which dissociate at 100-200 °C. Extreme ultraviolet (EUV) light stimulated photoemission from these diamondoid phosphonate monolayers exhibited a characteristic monochromatic NEA peak with 0.2 eV full width at half-maximum (fwhm) at room temperature, showing that the unique monochromatization property of diamondoids remained intact after attachment. Our results demonstrate that phosphonic dichloride functionality is a promising approach for forming stable diamondoid monolayers for elevated temperature and high-current applications such as electron emission and coatings in micro/nano electromechanical systems (MEMS/NEMS).

  View details for DOI 10.1021/la401781e

  View details for PubMedID 23855923

• High-Bandwidth AFM Probes for Imaging in Air and Fluid JOURNAL OF MICROELECTROMECHANICAL SYSTEMS Vijayraghavan, K., Gellineau, A. A., Wang, A., Butte, M. J., Melosh, N. A., Solgaard, O. 2013; 22 (3): 603-612

  View details for DOI 10.1109/JMEMS.2012.2235822

  View details for Web of Science ID 000319827700011

• Nanostraw-electroporation system for highly efficient intracellular delivery and transfection. ACS nano Xie, X., Xu, A. M., Leal-Ortiz, S., Cao, Y., Garner, C. C., Melosh, N. A. 2013; 7 (5): 4351-4358

  Abstract

  Nondestructive introduction of genes, proteins, and small molecules into mammalian cells with high efficiency is a challenging, yet critical, process. Here we demonstrate a simple nanoelectroporation platform to achieve highly efficient molecular delivery and high transfection yields with excellent uniformity and cell viability. The system is built on alumina nanostraws extending from a track-etched membrane, forming an array of hollow nanowires connected to an underlying microfluidic channel. Cellular engulfment of the nanostraws provides an intimate contact, significantly reducing the necessary electroporation voltage and increasing homogeneity over a large area. Biomolecule delivery is achieved by diffusion through the nanostraws and enhanced by electrophoresis during pulsing. The system was demonstrated to offer excellent spatial, temporal, and dose control for delivery, as well as providing high-yield cotransfection and sequential transfection.

  View details for DOI 10.1021/nn400874a

  View details for PubMedID 23597131

• Measurement of elastic properties in fluid using high bandwidth atomic force microscope probes APPLIED PHYSICS LETTERS Vijayraghavan, K., Wang, A., Solgaard, O., Butte, M. J., Melosh, N. A. 2013; 102 (10)

  View details for DOI 10.1063/1.4795598

  View details for Web of Science ID 000316501200074

• Nanostraw-Mediated Intracellular Delivery: Direct Observation of Cell/Nanotube Interfaces 57th Annual Meeting of the Biophysical-Society Xu, A. M., Aalipour, A., Melosh, N. A. CELL PRESS. 2013: 194A–194A

  View details for Web of Science ID 000316074301491

• Microbead-separated thermionic energy converter with enhanced emission current PHYSICAL CHEMISTRY CHEMICAL PHYSICS Littau, K. A., Sahasrabuddhe, K., Barfield, D., Yuan, H., Shen, Z., Howe, R. T., Melosh, N. A. 2013; 15 (34): 14442-14446

  Abstract

  The efficiency of thermionic energy converters is a strong function of the inter-electrode separation due to space-charge limitations. Here we demonstrate vacuum thermionic energy converters constructed using barium dispenser cathodes and thin film tungsten anodes, separated by size specific alumina microbeads for simple device fabrication and inter-electrode gap control. The current and device efficiency at the maximum power point are strongly dependent on the inter-electrode gap, with a maximum device efficiency of 0.61% observed for a gap on the order of 5 μm. Paths to further reductions in space charge and improved anode work function are outlined with potential for over an order of magnitude improvement in output power and efficiency.

  View details for DOI 10.1039/c3cp52895b

  View details for Web of Science ID 000322725000036

  View details for PubMedID 23881241

• Nanostraw–Electroporation System for Highly Efficient Intracellular Delivery and Transfection Acs Nano Xie, X., Xu, A., M., Leal-Ortiz, S., Cao, Y., Garner, C., C., Melosh, N., A. 2013
• Power-independent wavelength determination by hot carrier collection in metal-insulator-metal devices Nat Commun Wang, F., Melosh, N., A. 2013; 4: 1711
• Measurement of elastic properties in fluid using high bandwidth atomic force microscope probes Applied Physics Letters Vijayraghavan, K., Wang, A., Solgaard, O., Butte, M., J., Melosh, N., A. 2013; 102: 103111 (4 pp.)-103111 (4 pp.)
• Photon-enhanced thermionic emission from heterostructures with low interface recombination Nat Commun Schwede, J., W., Sarmiento, T., Narasimhan, V., K., Rosenthal, S., J., Riley, D., C., Schmitt, F., Melosh, Nicholas, A. 2013; 4: 1576
• Photon-enhanced thermionic emission from heterostructures with low interface recombination. Nature communications Schwede, J. W., Sarmiento, T., NARASIMHAN, V. K., Rosenthal, S. J., Riley, D. C., Schmitt, F., Bargatin, I., Sahasrabuddhe, K., Howe, R. T., Harris, J. S., Melosh, N. A., Shen, Z. 2013; 4: 1576-?

  Abstract

  Photon-enhanced thermionic emission is a method of solar-energy conversion that promises to combine photon and thermal processes into a single mechanism, overcoming fundamental limits on the efficiency of photovoltaic cells. Photon-enhanced thermionic emission relies on vacuum emission of photoexcited electrons that are in thermal equilibrium with a semiconductor lattice, avoiding challenging non-equilibrium requirements and exotic material properties. However, although previous work demonstrated the photon-enhanced thermionic emission effect, efficiency has until now remained very low. Here we describe electron-emission measurements on a GaAs/AlGaAs heterostructure that introduces an internal interface, decoupling the basic physics of photon-enhanced thermionic emission from the vacuum emission process. Quantum efficiencies are dramatically higher than in previous experiments because of low interface recombination and are projected to increase another order of magnitude with more stable, low work-function coatings. The results highlight the effectiveness of the photon-enhanced thermionic emission process and demonstrate that efficient photon-enhanced thermionic emission is achievable, a key step towards realistic photon-enhanced thermionic emission based energy conversion.

  View details for DOI 10.1038/ncomms2577

  View details for PubMedID 23481384

• Power-independent wavelength determination by hot carrier collection in metal-insulator-metal devices. Nature communications Wang, F., Melosh, N. A. 2013; 4: 1711-?

  Abstract

  Wavelength separation and detection is generally performed by spatial dispersal of incident light onto separate detectors, or by appropriate wavelength-selective filters. Here we demonstrate direct wavelength determination of monochromatic light in a power-independent fashion with a single metal-insulator-metal device. This simple platform allows facile fabrication and scaling, and may be useful for on-chip optical communications. Although a single wavelength is power-independent, with two or more concurrent input signals, the output obeys a simple current sum rule, allowing the output to be tuned by choosing the input wavelengths and power. Finally, we demonstrate real-time deconvolution of three different wavelength asynchronous signals.

  View details for DOI 10.1038/ncomms2728

  View details for PubMedID 23591878

• Photon-enhanced thermionic emission from heterostructures with low interface recombination. Nature communications Schwede, J. W., Sarmiento, T., NARASIMHAN, V. K., Rosenthal, S. J., Riley, D. C., Schmitt, F., Bargatin, I., Sahasrabuddhe, K., Howe, R. T., Harris, J. S., Melosh, N. A., Shen, Z. 2013; 4: 1576-?

  Abstract

  Photon-enhanced thermionic emission is a method of solar-energy conversion that promises to combine photon and thermal processes into a single mechanism, overcoming fundamental limits on the efficiency of photovoltaic cells. Photon-enhanced thermionic emission relies on vacuum emission of photoexcited electrons that are in thermal equilibrium with a semiconductor lattice, avoiding challenging non-equilibrium requirements and exotic material properties. However, although previous work demonstrated the photon-enhanced thermionic emission effect, efficiency has until now remained very low. Here we describe electron-emission measurements on a GaAs/AlGaAs heterostructure that introduces an internal interface, decoupling the basic physics of photon-enhanced thermionic emission from the vacuum emission process. Quantum efficiencies are dramatically higher than in previous experiments because of low interface recombination and are projected to increase another order of magnitude with more stable, low work-function coatings. The results highlight the effectiveness of the photon-enhanced thermionic emission process and demonstrate that efficient photon-enhanced thermionic emission is achievable, a key step towards realistic photon-enhanced thermionic emission based energy conversion.

  View details for DOI 10.1038/ncomms2577

  View details for PubMedID 23481384

• Photocathode device using diamondoid and cesium bromide films APPLIED PHYSICS LETTERS Clay, W. A., Maldonado, J. R., Pianetta, P., Dahl, J. E., Carlson, R. M., Schreiner, P. R., Fokin, A. A., Tkachenko, B. A., Melosh, N. A., Shen, Z. 2012; 101 (24)

  View details for DOI 10.1063/1.4769043

  View details for Web of Science ID 000312490000024

• A model for emission yield from planar photocathodes based on photon-enhanced thermionic emission or negative-electron-affinity photoemission JOURNAL OF APPLIED PHYSICS Sahasrabuddhe, K., Schwede, J. W., Bargatin, I., Jean, J., Howe, R. T., Shen, Z., Melosh, N. A. 2012; 112 (9)

  View details for DOI 10.1063/1.4764106

  View details for Web of Science ID 000311968400139

• Diamondoid coating enables disruptive approach for chemical and magnetic imaging with 10 nm spatial resolution APPLIED PHYSICS LETTERS Ishiwata, H., Acremann, Y., Scholl, A., Rotenberg, E., Hellwig, O., Dobisz, E., Doran, A., Tkachenko, B. A., Fokin, A. A., Schreiner, P. R., Dahl, J. E., Carlson, R. M., Melosh, N., Shen, Z., Ohldag, H. 2012; 101 (16)

  View details for DOI 10.1063/1.4756893

  View details for Web of Science ID 000310669300052

• Nanostraws for Direct Fluidic Intracellular Access NANO LETTERS VanDersarl, J. J., Xu, A. M., Melosh, N. A. 2012; 12 (8): 3881-3886

  Abstract

  Nanomaterials are promising candidates to improve the delivery efficiency and control of active agents such as DNA or drugs directly into cells. Here we demonstrate cell-culture platforms of nanotemplated "nanostraws" that pierce the cell membrane, providing a permanent fluidic pipeline into the cell for direct cytosolic access. Conventional polymeric track-etch cell culture membranes are alumina coated and etched to produce fields of nanostraws with controllable diameter, thickness, and height. Small molecules and ions were successfully transported into the cytosol with 40 and 70% efficiency, respectively, while GFP plasmids were successfully delivered and expressed. These platforms open the way for active, reproducible delivery of a wide variety of species into cells without endocytosis.

  View details for DOI 10.1021/nl204051v

  View details for Web of Science ID 000307211000001

  View details for PubMedID 22166016

• 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

  View details for PubMedCentralID PMC3495189

• Optimal emitter-collector gap for thermionic energy converters APPLIED PHYSICS LETTERS Lee, J., Bargatin, I., Melosh, N. A., Howe, R. T. 2012; 100 (17)

  View details for DOI 10.1063/1.4707379

  View details for Web of Science ID 000303340300106

• Mesoporous Thin-Film on Highly-Sensitive Resonant Chemical Sensor for Relative Humidity and CO2 Detection ANALYTICAL CHEMISTRY Lee, H. J., Park, K. K., Kupnik, M., Melosh, N. A., Khuri-Yakub, B. T. 2012; 84 (7): 3063-3066

  Abstract

  Distributed sensing of gas-phase chemicals is a promising application for mesoporous materials when combined with highly sensitive miniaturized gas sensors. We present a direct application of a mesoporous silica thin film on a highly sensitive miniaturized resonant chemical sensor with a mass sensitivity at the zeptogram scale for relative humidity and CO(2) detection. Using mesoporous silica thin-film, we report one of the lowest volume resolutions and a sensitive detection of 5.1 × 10(-4)% RH/Hz to water vapor in N(2), which is 70 times higher than a device with a nontemplated silica layer. In addition, a mesoporous thin-film that is functionalized with an amino-group is directly applied on the resonant sensor, which exhibits a volume sensitivity of 1.6 × 10(-4)%/Hz and a volume resolution of 1.82 × 10(-4)% to CO(2) in N(2).

  View details for DOI 10.1021/ac300225c

  View details for Web of Science ID 000302829800006

  View details for PubMedID 22372606

• MICROFABRICATED SILICON CARBIDE THERMIONIC ENERGY CONVERTER FOR SOLAR ELECTRICITY GENERATION 25th IEEE International Conference on Micro Electro Mechanical Systems (MEMS) Lee, J. H., Bargatin, I., Gwinn, T. O., Vincent, M., Littau, K. A., Maboudian, R., Shen, Z., Melosh, N. A., Howe, R. T. IEEE. 2012

  View details for Web of Science ID 000312912800317

• Diamondoid coating enables disruptive approach for chemical and magnetic imaging with 10 nm spatial resolution Applied Physics Letters Ishiwata, H., Acremann, Y., Scholl, A., Rotenberg, E., Hellwig, O., Dobisz, E., Melosh, Nicholas, A. 2012; 101: 163101 (5 pp.)-163101 (5 pp.)163101 (5 pp.)
• Optimal emitter-collector gap for thermionic energy converters Applied Physics Letters Lee, J., H., Bargatin, I., Melosh, N., A., Howe, R., T. 2012; 100
• A model for emission yield from planar photocathodes based on photon-enhanced thermionic emission or negative-electron-affinity photoemission Journal of Applied Physics Sahasrabuddhe, K., Schwede, J., W., Bargatin, I., Jean, J., Howe, R., T., Shen, Z., X., Melosh, Nicholas, A. 2012; 112: 094907 (10 pp.)-094907 (10 pp.)094907 (10 pp.)
• Photocathode device using diamondoid and cesium bromide films Applied Physics Letters Clay, W., A., Maldonado, J., R., Pianetta, P., Dahl, J., E.P., Carlson, R., M.K., Schreiner, P., R., Melosh, Nicholas, A. 2012; 101: 241605 (5 pp.)-241605 (5 pp.)
• Plasmonic Energy Collection through Hot Carrier Extraction NANO LETTERS Wang, F., Melosh, N. A. 2011; 11 (12): 5426-5430

  Abstract

  Conversion of light into direct current is important for applications ranging from energy conversion to photodetection, yet often challenging over broad photon frequencies. Here we show a new architecture based on surface plasmon excitation within a metal-insulator-metal device that produces power based on spatial confinement of electron excitation through plasmon absorption. Plasmons excited in the upper metal are absorbed, creating a high concentration of hot electrons which can inject above or tunnel through the thin insulating barrier, producing current. The theoretical power conversion efficiency enhancement achieved can be almost 40 times larger than that of direct illumination while utilizing a broad spectrum of IR to visible wavelengths. Here we present both theoretical estimates of the power conversion efficiency and experimental device measurements, which show clear rectification and power conversion behavior.

  View details for DOI 10.1021/nl203196z

  View details for Web of Science ID 000297950200056

  View details for PubMedID 22023372

• Photoluminescence of diamondoid crystals JOURNAL OF APPLIED PHYSICS Clay, W. A., Sasagawa, T., Iwasa, A., Liu, Z., Dahl, J. E., Carlson, R. M., Kelly, M., Melosh, N., Shen, Z. 2011; 110 (9)

  View details for DOI 10.1063/1.3657522

  View details for Web of Science ID 000297062100028

• Molecular Structure Influences the Stability of Membrane Penetrating Biointerfaces NANO LETTERS Almquist, B. D., Melosh, N. A. 2011; 11 (5): 2066-2070

  Abstract

  Nanoscale patterning of hydrophobic bands on otherwise hydrophilic surfaces allows integration of inorganic structures through biological membranes, reminiscent of transmembrane proteins. Here we show that a set of innate molecular properties of the self-assembling hydrophobic band determine the resulting interface stability. Surprisingly, hydrophobicity is found to be a secondary factor with monolayer crystallinity the major determinate of interface strength. These results begin to establish guidelines for seamless bioinorganic integration of nanoscale probes with lipid membranes.

  View details for DOI 10.1021/nl200542m

  View details for Web of Science ID 000290373000037

  View details for PubMedID 21469728

• Engineering cell access with nano-functionalized posts 241st National Meeting and Exposition of the American-Chemical-Society (ACS) Verma, P., Tayebi, N., Almquist, B., Melosh, N. AMER CHEMICAL SOC. 2011

  View details for Web of Science ID 000291982803522

• Plasmonic energy collection through hot carrier extraction Nano Letters Wang, F., Melosh, N., A. 2011; 11: 5426-30
• Photoluminescence of Diamond Crystals Journal of Applied Physics Clay, W., A., Sasagawa, T., Iwasa, A., Liu, Z., Dahl, J., E., Carlson, R., M.K., Melosh, Nicholas, A. 2011
• Nanostraws for Direct Fluidic Intracellular Access Nano Letters Vandersarl, J., J., Xu, A., M., Melosh, N., A. 2011
• Rapid spatial and temporal controlled signal delivery over large cell culture areas LAB ON A CHIP VanDersarl, J. J., Xu, A. M., Melosh, N. A. 2011; 11 (18): 3057-3063

  Abstract

  Controlled chemical delivery in microfluidic cell culture devices often relies on slowly evolving diffusive gradients, as the spatial and temporal control provided by fluid flow results in significant cell-perturbation. In this paper we introduce a microfluidic device architecture that allows for rapid spatial and temporal soluble signal delivery over large cell culture areas without fluid flow over the cells. In these devices the cell culture well is divided from a microfluidic channel located directly underneath the chamber by a nanoporous membrane. This configuration requires chemical signals in the microchannel to only diffuse through the thin membrane into large cell culture area, rather than diffuse in from the sides. The spatial chemical pattern within the microfluidic channel was rapidly transferred to the cell culture area with good fidelity through diffusion. The cellular temporal response to a step-function signal showed that dye reached the cell culture surface within 45 s, and achieved a static concentration in under 6 min. Chemical pulses of less than one minute were possible by temporally alternating the signal within the microfluidic channel, enabling rapid flow-free chemical microenvironment control for large cell culture areas.

  View details for DOI 10.1039/c1lc20311h

  View details for Web of Science ID 000294263400004

  View details for PubMedID 21805010

• Nanoscale patterning controls inorganic-membrane interface structure NANOSCALE Almquist, B. D., Verma, P., Cai, W., Melosh, N. A. 2011; 3 (2): 391-400

  Abstract

  The ability to non-destructively integrate inorganic structures into or through biological membranes is essential to realizing full bio-inorganic integration, including arrayed on-chip patch-clamps, drug delivery, and biosensors. Here we explore the role of nanoscale patterning on the strength of biomembrane-inorganic interfaces. AFM measurements show that inorganic probes functionalized with hydrophobic bands with thicknesses complimentary to the hydrophobic lipid bilayer core exhibit strong attachment in the bilayer. As hydrophobic band thickness increases to 2-3 times the bilayer core the interfacial strength decreases, comparable to homogeneously hydrophobic probes. Analytical calculations and molecular dynamics simulations predict a transition between a 'fused' interface and a 'T-junction' that matches the experimental results, showing lipid disorder and defect formation for thicker bands. These results show that matching biological length scales leads to more intimate bio-inorganic junctions, enabling rational design of non-destructive membrane interfaces.

  View details for DOI 10.1039/c0nr00486c

  View details for Web of Science ID 000287363500006

  View details for PubMedID 20931126

• Theoretical analysis of hot electron collection in metal-insulator-metal devices Conference on Next Generation (Nano) Photonic and Cell Technologies for Solar Energy Conversion II Wang, F., Melosh, N. A. SPIE-INT SOC OPTICAL ENGINEERING. 2011

  View details for DOI 10.1117/12.894250

  View details for Web of Science ID 000303797800011

• ENZYME ASSAYS Detection by failure NATURE CHEMISTRY Melosh, N. A. 2010; 2 (12): 1006-1007

  View details for DOI 10.1038/nchem.914

  View details for Web of Science ID 000284527300004

  View details for PubMedID 21107359

• Effects of tip-induced material reorganization in dynamic force spectroscopy PHYSICAL REVIEW E Hager-Barnard, E. A., Melosh, N. A. 2010; 82 (3)

  Abstract

  Dynamic force spectroscopy (DFS) has become a well-established method for characterizing bond strength, yet may also be useful for examining more complex phenomena such as dynamic processes or multiple reaction pathways. Here, we analyze the case where contact between an atomic force microscopy (AFM) tip and the sample induces sample reorganization during testing. Surface contact often causes molecular rearrangement in soft materials, which could also result in an altered reaction energy landscape. We model this situation by allowing the energy barrier position and magnitude to be time-dependent functions with a characteristic time scale τ . We find dynamic energy barriers result in two linear regimes with a dramatic transition near t=τ in the DFS analysis. The sharp transition region is a hallmark of a moving energy barrier and indicates the time scale of reorganization. These results illustrate that DFS may be useful to monitor dynamic transitions and also highlight the importance of extending the loading rate range used in DFS studies.

  View details for DOI 10.1103/PhysRevE.82.031911

  View details for Web of Science ID 000282133400008

  View details for PubMedID 21230112

• Photon-enhanced thermionic emission for solar concentrator systems NATURE MATERIALS Schwede, J. W., Bargatin, I., Riley, D. C., Hardin, B. E., Rosenthal, S. J., Sun, Y., Schmitt, F., Pianetta, P., Howe, R. T., Shen, Z., Melosh, N. A. 2010; 9 (9): 762-767

  Abstract

  Solar-energy conversion usually takes one of two forms: the 'quantum' approach, which uses the large per-photon energy of solar radiation to excite electrons, as in photovoltaic cells, or the 'thermal' approach, which uses concentrated sunlight as a thermal-energy source to indirectly produce electricity using a heat engine. Here we present a new concept for solar electricity generation, photon-enhanced thermionic emission, which combines quantum and thermal mechanisms into a single physical process. The device is based on thermionic emission of photoexcited electrons from a semiconductor cathode at high temperature. Temperature-dependent photoemission-yield measurements from GaN show strong evidence for photon-enhanced thermionic emission, and calculated efficiencies for idealized devices can exceed the theoretical limits of single-junction photovoltaic cells. The proposed solar converter would operate at temperatures exceeding 200 degrees C, enabling its waste heat to be used to power a secondary thermal engine, boosting theoretical combined conversion efficiencies above 50%.

  View details for DOI 10.1038/NMAT2814

  View details for Web of Science ID 000281178400029

  View details for PubMedID 20676086

• Gigaohm resistance membrane seals with stealth probe electrodes APPLIED PHYSICS LETTERS Verma, P., Melosh, N. A. 2010; 97 (3)

  View details for DOI 10.1063/1.3464954

  View details for Web of Science ID 000280255800104

• An Electrostatic Model for DNA Surface Hybridization BIOPHYSICAL JOURNAL Wong, I. Y., Melosh, N. A. 2010; 98 (12): 2954-2963

  Abstract

  DNA hybridization at surfaces is a crucial process for biomolecular detection, genotyping, and gene expression analysis. However, hybridization density and kinetics can be strongly inhibited by electric fields from the negatively charged DNA as the reaction proceeds. Here, we develop an electrostatic model to optimize hybridization density and kinetics as a function of DNA surface density, salt concentrations, and applied voltages. The electrostatic repulsion from a DNA surface layer is calculated numerically and incorporated into a modified Langmuir scheme, allowing kinetic suppression of hybridization. At the low DNA probe densities typically used in assays (<10(13)/cm(2)), electrostatics effects are largely screened and hybridization is completed with fast kinetics. However, higher hybridization densities can be achieved at intermediate DNA surface densities, albeit with slower kinetics. The application of positive voltages circumvents issues resulting from the very high DNA probe density, allowing highly enhanced hybridization densities and accelerated kinetics, and validating recent experimental measurements.

  View details for DOI 10.1016/j.bpj.2010.03.017

  View details for Web of Science ID 000278913500024

  View details for PubMedID 20550908

• Dynamic actuation using nano-bio interfaces MATERIALS TODAY Wong, I. Y., Almquist, B. D., Melosh, N. A. 2010; 13 (6): 14-22

  View details for Web of Science ID 000278390600010

• Continuum model of mechanical interactions between biological cells and artificial nanostructures BIOINTERPHASES Verma, P., Wong, I. Y., Melosh, N. A. 2010; 5 (2): 37-44

  Abstract

  The controlled insertion of artificial nanostructures into biological cells has been utilized for patch clamping, targeted drug delivery, cell lysing, and cell mechanics measurements. In this work, an elastic continuum model is implemented to treat the deformation of spherical cells in solution due to their interaction with cylindrical probes. At small deformations, the force varies nonlinearly with indentation due to global deformation of the cell shape. However, at large indentations, the force varies linearly with indentation due to more localized deformations. These trends are consistent with experimental measurements under comparable conditions and can be used to develop design rules for optimizing probe-cell interactions.

  View details for DOI 10.1116/1.3431960

  View details for Web of Science ID 000282333300003

  View details for PubMedID 20831347

• Single-Step Process to Reconstitute Cell Membranes on Solid Supports LANGMUIR Mager, M. D., Melosh, N. A. 2010; 26 (7): 4635-4638

  Abstract

  A new technique is presented to create supported lipid bilayers from whole cell lipids without the use of detergent or solvent extraction. In a modification of the bubble collapse deposition (BCD) technique, an air bubble is created underwater and brought into contact with a population of cells. The high-energy air/water interface extracts the lipid component of the cell membrane, which can subsequently be redeposited as a fluid bilayer on another substrate. The resulting bilayers were characterized with fluorescence microscopy, and it was found that both leaflets of the cell membrane are transferred but the cytoskeleton is not. The resulting supported bilayer was fluid over an area much larger than a single cell, demonstrating the capacity to create large, continuous bilayer samples. This capability to create fluid, biologically relevant bilayers will facilitate the use of high-resolution scanning microscopy techniques in the study of membrane-related processes.

  View details for DOI 10.1021/la100583f

  View details for Web of Science ID 000275995100020

  View details for PubMedID 20205459

• Fusion of biomimetic stealth probes into lipid bilayer cores PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Almquist, B. D., Melosh, N. A. 2010; 107 (13): 5815-5820

  Abstract

  Many biomaterials are designed to regulate the interactions between artificial and natural surfaces. However, when materials are inserted through the cell membrane itself the interface formed between the interior edge of the membrane and the material surface is not well understood and poorly controlled. Here we demonstrate that by replicating the nanometer-scale hydrophilic-hydrophobic-hydrophilic architecture of transmembrane proteins, artificial "stealth" probes spontaneously insert and anchor within the lipid bilayer core, forming a high-strength interface. These nanometer-scale hydrophobic bands are readily fabricated on metallic probes by functionalizing the exposed sidewall of an ultrathin evaporated Au metal layer rather than by lithography. Penetration and adhesion forces for butanethiol and dodecanethiol functionalized probes were directly measured using atomic force microscopy (AFM) on thick stacks of lipid bilayers to eliminate substrate effects. The penetration dynamics were starkly different for hydrophobic versus hydrophilic probes. Both 5- and 10 nm thick hydrophobically functionalized probes naturally resided within the lipid core, while hydrophilic probes remained in the aqueous region. Surprisingly, the barrier to probe penetration with short butanethiol chains (E(o,5 nm) = 21.8k(b)T, E(o,10 nm) = 15.3k(b)T) was dramatically higher than longer dodecanethiol chains (E(o,5 nm) = 14.0k(b)T, E(o,10 nm) = 10.9k(b)T), indicating that molecular mobility and orientation also play a role in addition to hydrophobicity in determining interface stability. These results highlight a new strategy for designing artificial cell interfaces that can nondestructively penetrate the lipid bilayer.

  View details for DOI 10.1073/pnas.0909250107

  View details for Web of Science ID 000276159500024

  View details for PubMedID 20212151

• Lateral fusion of lipid membranes to nanoscale functionalized Almquist, B., Melosh, N. AMER CHEMICAL SOC. 2010

  View details for Web of Science ID 000208189302023

• Clathrin protein assemblies as a biotemplate VanDersarl, J. J., Melosh, N. A. AMER CHEMICAL SOC. 2010

  View details for Web of Science ID 000208189301895

• AFM force spectroscopy on TAT membrane penetration Hager-Barnard, E. A., Almquist, B. D., Melosh, N. A. AMER CHEMICAL SOC. 2010

  View details for Web of Science ID 000208189302025

• Gigaohm resistance membrane seals with stealth probe electrodes Applied Physics Letters Verma, P., Melosh, N., A. 2010; 97
• Fusion of Biomimetic ‘Stealth’ Probes into Lipid Bilayer Cores Almquist, B., D., Melosh, N., A. 2010
• Effects of tip-induced material reorganization in dynamic force spectroscopy Phys. Rev. E Hager-Barnard, E., Melosh, N., A. 2010; 82: 31911
• ENZYME ASSAYS: Detection by failure Nature Chemistry Melosh, N., A. 2010; 2: 1006-1007
• Directed Hybridization and Melting of DNA Linkers using Counterion-Screened Electric Fields NANO LETTERS Wong, I. Y., Melosh, N. A. 2009; 9 (10): 3521-3526

  Abstract

  Dynamic self-assembly using responsive, "smart" materials such as DNA is a promising route toward reversible assembly and patterning of nanostructures for error-corrected fabrication, enhanced biosensors, drug delivery and gene therapy. DNA linkers were designed with strategically placed mismatches, allowing rapid attachment and release from a surface in a counterion-screened electric field. These electrostatic fields are inherently highly localized, directing assembly with nanometer precision while avoiding harmful electrochemical reactions. We show that depending on the sign of the applied field, the DNA hybridization density is strongly enhanced or diminished due to the high negative charge density of immobilized DNA. This use of dynamic fields rather than static templates enables fabrication of heterogeneously hybridized electrodes with different functional moieties, despite the use of identical linker sequences.

  View details for DOI 10.1021/nl901710n

  View details for Web of Science ID 000270670500025

  View details for PubMedID 19606816

• Determining orientational structure of diamondoid thiols attached to silver using near-edge X-ray absorption fine structure spectroscopy JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA Willey, T. M., Lee, J. R., Fabbri, J. D., Wang, D., Nielsen, M. H., Randel, J. C., Schreiner, P. R., Fokin, A. A., Tkachenko, B. A., Fokina, N. A., Dahl, J. E., Carlson, R. M., Terminello, L. J., Melosh, N. A., van Buuren, T. 2009; 172 (1-3): 69-77

  View details for DOI 10.1016/j.elspec.2009.03.011

  View details for Web of Science ID 000267561500011

• Influence of electrostatic fields in self assembly Melosh, N. A. AMER CHEMICAL SOC. 2009

  View details for Web of Science ID 000207857807784

• Identification and Passivation of Defects in Self-Assembled Monolayers LANGMUIR Preiner, M. J., Melosh, N. A. 2009; 25 (5): 2585-2587

  Abstract

  We demonstrate imaging of nanoscale defects in self-assembled monolayers (SAMs). Atomic layer deposition of aluminum oxide (AlO(x)) onto hydrophobic SAMs is followed by imaging using scanning electron microscopy (SEM). The insulating AlO(x) selectively deposits onto the exposed substrate at defect sites and becomes charged during imaging, providing high contrast even for nanometer scale defects. The deposited AlO(x) also acts as a barrier for electron transfer, thereby simultaneously electrically passivating the defects in the SAM as it labels them.

  View details for DOI 10.1021/la804162a

  View details for Web of Science ID 000263770800009

  View details for PubMedID 19437743

• Origin of the Monochromatic Photoemission Peak in Diamondoid Monolayers NANO LETTERS Clay, W. A., Liu, Z., Yang, W., Fabbri, J. D., Dahl, J. E., Carlson, R. M., Sun, Y., Schreiner, P. R., Fokin, A. A., Tkachenko, B. A., Fokina, N. A., Pianetta, P. A., Melosh, N., Shen, Z. 2009; 9 (1): 57-61

  Abstract

  Recent photoemission experiments have discovered a highly monochromatized secondary electron peak emitted from diamondoid self-assembled monolayers on metal substrates. New experimental data and simulation results are presented to show that a combination of negative electron affinity and strong electron-phonon scattering is responsible for this behavior. The simulation results are generated using a simple Monte Carlo transport algorithm. The simulated spectra recreate the main spectral features of the measured ones.

  View details for DOI 10.1021/nl802310k

  View details for Web of Science ID 000262519100010

  View details for PubMedID 18975993

• An Internally Amplified Signal SOI Nano-bridge Biosensor for Electrical Detection of DNA Hybridization IEEE International SOI Conference 2009 Parizi, K. B., Melosh, N., Nishi, Y. IEEE. 2009: 67–68

  View details for Web of Science ID 000276151400029

• Determining orientational structure of diamondoid thiols attached to silver using near-edge X-ray absorption fine structure spectroscopy Journal of Electron Spectroscopy and Related Phenomena Willey, T., M., Lee, J., R.I., Fabbri, J., D., Wang, D., Nielsen, M., H., Randel, J., C., Melosh, Nicholas, A. 2009; 172: 69-77
• Nanopore-Spanning Lipid Bilayers for Controlled Chemical Release ADVANCED MATERIALS Mager, M. D., Melosh, N. A. 2008; 20 (23): 4423-4427

  View details for DOI 10.1002/adma.200800969

  View details for Web of Science ID 000261937300012

• Formation and Characterization of Fluid Lipid Bilayers on Alumina LANGMUIR Mager, M. D., Almquist, B., Melosh, N. A. 2008; 24 (22): 12734-12737

  Abstract

  Fluid lipid bilayers were deposited on alumina substrates with the use of bubble collapse deposition (BCD). Previous studies using vesicle rupture have required the use of charged lipids or surface functionalization to induce bilayer formation on alumina, but these modifications are not necessary with BCD. Photobleaching experiments reveal that the diffusion coefficient of POPC on alumina is 0.6 microm (2)/s, which is much lower than the 1.4-2.0 microm (2)/s reported on silica. Systematically accounting for roughness, immobile regions and membrane viscosity shows that pinning sites account for about half of this drop in diffusivity. The remainder of the difference is attributed to a more tightly bound water state on the alumina surface, which induces a larger drag on the bilayer.

  View details for DOI 10.1021/la802726u

  View details for Web of Science ID 000260874800004

  View details for PubMedID 18942863

• Diamondoids as low-kappa dielectric materials APPLIED PHYSICS LETTERS Clay, W. A., Sasagawa, T., Kelly, M., Dahl, J. E., Carlson, R. M., Melosh, N., Shen, Z. 2008; 93 (17)

  View details for DOI 10.1063/1.3010379

  View details for Web of Science ID 000260571800066

• Near-edge X-ray absorption fine structure spectroscopy of diamondoid thiol monolayers on gold JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Willey, T. M., Fabbri, J. D., Lee, J. R., Schreiner, P. R., Fokin, A. A., Tkachenko, B. A., Fokina, N. A., Dahl, J. E., Carlson, R. M., Vance, A. L., Yang, W., Terminello, L. J., van Buuren, T., Melosh, N. A. 2008; 130 (32): 10536-10544

  Abstract

  Diamondoids, hydrocarbon molecules with cubic-diamond-cage structures, have unique properties with potential value for nanotechnology. The availability and ability to selectively functionalize this special class of nanodiamond materials opens new possibilities for surface modification, for high-efficiency field emitters in molecular electronics, as seed crystals for diamond growth, or as robust mechanical coatings. The properties of self-assembled monolayers (SAMs) of diamondoids are thus of fundamental interest for a variety of emerging applications. This paper presents the effects of thiol substitution position and polymantane order on diamondoid SAMs on gold using near-edge X-ray absorption fine structure spectroscopy (NEXAFS) and X-ray photoelectron spectroscopy (XPS). A framework to determine both molecular tilt and twist through NEXAFS is presented and reveals highly ordered diamondoid SAMs, with the molecular orientation controlled by the thiol location. C 1s and S 2p binding energies are lower in adamantane thiol than alkane thiols on gold by 0.67 +/- 0.05 and 0.16 +/- 0.04 eV, respectively. These binding energies vary with diamondoid monolayer structure and thiol substitution position, consistent with different degrees of steric strain and electronic interaction with the substrate. This work demonstrates control over the assembly, in particular the orientational and electronic structure, providing a flexible design of surface properties with this exciting new class of diamond nanoparticles.

  View details for DOI 10.1021/ja711131e

  View details for Web of Science ID 000258293800038

  View details for PubMedID 18642809

• Interfacial effects in thin films of polymeric semiconductors JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B Rivnay, J., Jimison, L. H., Toney, M. F., Preiner, M., Melosh, N. A., Salleo, A. 2008; 26 (4): 1454-1460

  View details for DOI 10.1116/1.2952454

  View details for Web of Science ID 000258494400036

• Electronically activated actin protein polymerization and alignment JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Wong, I. Y., Footer, M. J., Melosh, N. A. 2008; 130 (25): 7908-7915

  Abstract

  Biological systems are the paragon of dynamic self-assembly, using a combination of spatially localized protein complexation, ion concentration, and protein modification to coordinate a diverse set of self-assembling components. Biomimetic materials based upon biologically inspired design principles or biological components have had some success at replicating these traits, but have difficulty capturing the dynamic aspects and diversity of biological self-assembly. Here, we demonstrate that the polymerization of ion-sensitive proteins can be dynamically regulated using electronically enhanced ion mixing and monomer concentration. Initially, the global activity of the cytoskeletal protein actin is inhibited using a low-ionic strength buffer that minimizes ion complexation and protein-protein interactions. Nucleation and growth of actin filaments are then triggered by a low-frequency AC voltage, which causes local enhancement of the actin monomer concentration and mixing with Mg(2+). The location and extent of polymerization are governed by the voltage and frequency, producing highly ordered structures unprecedented in bulk experiments. Polymerization rate and filament orientation could be independently controlled using a combination of low-frequency (approximately 100 Hz) and high frequency (1 MHz) AC voltages, creating a range of macromolecular architectures from network hydrogel microparticles to highly aligned arrays of actin filaments with approximately 750 nm periodicity. Since a wide range of proteins are activated upon complexation with charged species, this approach may be generally applicable to a variety of biopolymers and proteins.

  View details for DOI 10.1021/ja7103284

  View details for Web of Science ID 000256962000042

  View details for PubMedID 18507467

• Creating large area molecular electronic junctions using atomic layer deposition APPLIED PHYSICS LETTERS Preiner, M. J., Melosh, N. A. 2008; 92 (21)

  View details for DOI 10.1063/1.2917870

  View details for Web of Science ID 000256303500073

• A nonvolatile plasmonic switch employing photochromic molecules NANO LETTERS Pala, R. A., Shimizu, K. T., Melosh, N. A., Brongersma, M. L. 2008; 8 (5): 1506-1510

  Abstract

  We demonstrate a surface plasmon-polariton (SPP) waveguide all-optical switch that combines the unique physical properties of small molecules and metallic (plasmonic) nanostructures. The switch consists of a pair of gratings defined in an aluminum film coated with a 65 nm thick layer of photochromic (PC) molecules. The first grating couples a signal beam consisting of free space photons to SPPs that interact effectively with the PC molecules. These molecules can reversibly be switched between transparent and absorbing states using a free space optical pump. In the transparent (signal "on") state, the SPPs freely propagate through the molecular layer, and in the absorbing (signal "off") state, the SPPs are strongly attenuated. The second grating serves to decouple the SPPs back into a free space optical beam, enabling measurement of the modulated signal with a far-field detector. In a preliminary study, the switching behavior of the PC molecules themselves was confirmed and quantified by surface plasmon resonance spectroscopy. The excellent (16%) overlap of the SPP mode profile with the thin layer of switching molecules enabled efficient switching with power densities of approximately 6.0 mW/cm2 in 1.5 microm x 8 microm devices, resulting in plasmonic switching powers of 0.72 nW per device. Calculations further showed that modulation depths in access of 20 dB can easily be attained in optimized designs. The quantitative experimental and theoretical analysis of the nonvolatile switching behavior in this letter guides the design of future nanoscale optically or electrically pumped optical switches.

  View details for DOI 10.1021/nl0808839

  View details for Web of Science ID 000255906400042

  View details for PubMedID 18412401

• Efficient optical coupling into metal-insulator-metal plasmon modes with subwavelength diffraction gratings APPLIED PHYSICS LETTERS Preiner, M. J., Shimizu, K. T., White, J. S., Melosh, N. A. 2008; 92 (11)

  View details for DOI 10.1063/1.2898509

  View details for Web of Science ID 000254292400085

• Suspension of nanoparticles in SU-8: Processing and characterization of nanocomposite polymers European Nano System Conference (ENS '05) Chiamori, H. C., Brown, J. W., Adhiprakasha, E. V., Hantsoo, E. T., Straalsund, J. B., Melosh, N. A., Pruitt, B. L. ELSEVIER SCI LTD. 2008: 228–36

  View details for DOI 10.1016/j.mejo.2007.05.012

  View details for Web of Science ID 000253562400010

• Creating large area molecular electronic junctions using atomic layer deposition Applied Physics Letters Preiner, M., J., Melosh, N., A. 2008; 92
• Efficient optical coupling into metal-insulator-metal plasmon modes with subwavelength diffraction gratings Applied Physics Letters Preiner, M., J., Shimizu, K., T., White, J., S., Melosh, N., A. 2008; 92: 113109-1-3
• Diamondoids as low-kappa dielectric materials Applied Physics Letters Clay, W., A., Sasagawa, T., Kelly, M., Dahl, J., E., Carlson, R., M.K., Melosh, N. 2008; 93: 172901
• Lipid bilayer deposition and patterning via air bubble collapse LANGMUIR Mager, M. D., Melosh, N. A. 2007; 23 (18): 9369-9377

  Abstract

  We report a new method for forming patterned lipid bilayers on solid substrates. In bubble collapse deposition (BCD), an air bubble is first "inked" with a monolayer of phospholipid molecules and then touched to the surface of a thermally oxidized silicon wafer and the air is slowly withdrawn. As the bubble shrinks, the lipid monolayer pressure increases. Once the monolayer exceeds the collapse pressure, it folds back on itself, depositing a stable lipid bilayer on the surface. These bilayer disks have lateral diffusion coefficients consistent with high quality supported bilayers. By sequentially depositing bilayers in overlapping areas, fluid connections between bilayers of different compositions are formed. Performing vesicle rupture on the open substrate surrounding this bilayer patch results in a fluid but spatially isolated bilayer. Very little intermixing was observed between the vesicle rupture and bubble-deposited bilayers.

  View details for DOI 10.1021/la701372b

  View details for Web of Science ID 000248886700037

  View details for PubMedID 17683151

• COLL 108-Lateral fusion of lipid membranes to nanoscale functionalized posts Almquist, B. D., Melosh, N. A. AMER CHEMICAL SOC. 2007

  View details for Web of Science ID 000207593902029

• BIOT 53-Nanoscale reservoirs for spatially and temporally controlled biointerfaces Melosh, N. A., VanDersarl, J. J., Hagar-Barnard, E., Yenilmez, E. AMER CHEMICAL SOC. 2007

  View details for Web of Science ID 000207593903212

• Monochromatic electron photoemission from diamondoid monolayers SCIENCE Yang, W. L., Fabbri, J. D., Willey, T. M., Lee, J. R., Dahl, J. E., Carlson, R. M., Schreiner, P. R., Fokin, A. A., Tkachenko, B. A., Fokina, N. A., Meevasana, W., Mannella, N., Tanaka, K., Zhou, X. J., van Buuren, T., Kelly, M. A., Hussain, Z., Melosh, N. A., Shen, Z. 2007; 316 (5830): 1460-1462

  Abstract

  We found monochromatic electron photoemission from large-area self-assembled monolayers of a functionalized diamondoid, [121]tetramantane-6-thiol. Photoelectron spectra of the diamondoid monolayers exhibited a peak at the low-kinetic energy threshold; up to 68% of all emitted electrons were emitted within this single energy peak. The intensity of the emission peak is indicative of diamondoids being negative electron affinity materials. With an energy distribution width of less than 0.5 electron volts, this source of monochromatic electrons may find application in technologies such as electron microscopy, electron beam lithography, and field-emission flat-panel displays.

  View details for DOI 10.1126/science.1141811

  View details for Web of Science ID 000247066400037

  View details for PubMedID 17556579

• Dynamic control of biomolecular activity using electrical interfaces SOFT MATTER Wong, I. Y., Footer, M. J., Melosh, N. A. 2007; 3 (3): 267-274

  View details for DOI 10.1039/b607279h

  View details for Web of Science ID 000246006700003

• Monochromatic Electron Emission from Negative Electron Affinity Diamondoid Monolayers Science Yang, W., L., Fabbri, J., D., Willey, T., M., Lee, J., R.I., Dahl, J., E., Carlson, R., M.K., Melosh, Nicholas, A. 2007; 315: 1460-1462
• Probing molecular junctions using surface plasmon resonance spectroscopy NANO LETTERS Shimizu, K. T., Pala, R. A., Fabbri, J. D., Brongersma, M. L., Melosh, N. A. 2006; 6 (12): 2797-2803

  Abstract

  The optical absorption spectra of nanometer-thick organic films and molecular monolayers sandwiched between two metal contacts have been measured successfully using surface plasmon resonance spectroscopy (SPRS). The electric field within metal-insulator (organic)-metal (MIM) cross-bar junctions created by surface plasmon-polaritons excited on the metal surface allows sensitive measurement of molecular optical properties. Specifically, this spectroscopic technique extracts the real and imaginary indices of the organic layer for each wavelength of interest. The SPRS sensitivity was calculated for several device architectures, metals, and layer thicknesses to optimize the organic film absorptivity measurements. Distinct optical absorption features were clearly observed for R6G layers as thin as a single molecular monolayer between two metal electrodes. This method also enables dynamic measurement of molecular conformation inside metallic junctions, as shown by following the optical switching of a thin spiropyran/polymer film upon exposure to UV light. Finally, optical and electrical measurements can be made simultaneously to study the effect of electrical bias and current on molecular conformation, which may have significant impact in areas such as molecular and organic electronics.

  View details for DOI 10.1021/nl061893h

  View details for Web of Science ID 000242786500029

  View details for PubMedID 17163708

• Soft deposition of large-area metal contacts for molecular electronics ADVANCED MATERIALS Shimizu, K. T., Fabbri, J. D., Jelincic, J. J., Melosh, N. A. 2006; 18 (12): 1499-?

  View details for DOI 10.1002/adma.200600195

  View details for Web of Science ID 000238727100002

• Soft Deposition of Large Area Metal Contacts for Molecular Electronics Advanced Materials Shimizu, K., T., Fabbri, J., D., Jelincic, J., J., Melosh, N., A. 2006; 18: 1499-1504
• Probing molecular junctions using surface plasmon resonance spectroscopy Nano Letters Shimizu, K., T., Pala, R., A., Fabbri, J., D., Brongersma, M., L., Melosh, N., A. 2006; 6: 2797-2803
• Silicon chip-based patch-clamp electrodes integrated with PDMS microfluidics 49th Annual Meeting of the Biophysical-Society Nagarah, J. M., Wang, P., Luo, Y., Pantoja, R., Melosh, N. A., Starace, D. M., Blunk, R., Bezanilla, F., Heath, J. R. CELL PRESS. 2005: 522A–522A

  View details for Web of Science ID 000226378502555

• Fabrication of conducting Si nanowire arrays JOURNAL OF APPLIED PHYSICS Beckman, R. A., Johnston-Halperin, E., Melosh, N. A., Luo, Y., Green, J. E., Heath, J. R. 2004; 96 (10): 5921-5923

  View details for DOI 10.1063/1.1801155

  View details for Web of Science ID 000224926000089

• Silicon chip-based patch-clamp electrodes integrated with PDMS microfluidics BIOSENSORS & BIOELECTRONICS Pantoja, R., Nagarah, J. M., Starace, D. M., Melosh, N. A., Blunck, R., Bezanilla, F., Heath, J. R. 2004; 20 (3): 509-517

  Abstract

  We report on a silicon wafer-based device that can be used for recording macroscopic ion channel protein activities across a diverse group of cell-types. Gigaohm seals were achieved for CHO-K1 and RIN m5F cells, and both cell-attached and whole-cell mode configurations were also demonstrated. Two distinct intrinsic potassium ion channels were recorded in whole-cell mode for HIT-T15 and RAW 264.7 cells. Polydimethylsiloxane (PDMS) microfluidics were also coupled with the micromachined silicon chips in order to demonstrate that a single cell could be selectively directed to a micropore, and membrane protein currents could subsequently be recorded. These silicon chip-based devices have significant advantages over traditional micropipette approaches, and may serve as combinatorial tools for investigating membrane biophysics, pharmaceutical screening, and other bio-sensing tasks.

  View details for DOI 10.1016/j.bios.2004.02.020

  View details for Web of Science ID 000225009000016

  View details for PubMedID 15494233

• Ultrahigh-density nanowire lattices and circuits SCIENCE Melosh, N. A., Boukai, A., Diana, F., Gerardot, B., Badolato, A., Petroff, P. M., Heath, J. R. 2003; 300 (5616): 112-115

  Abstract

  We describe a general method for producing ultrahigh-density arrays of aligned metal and semiconductor nanowires and nanowire circuits. The technique is based on translating thin film growth thickness control into planar wire arrays. Nanowires were fabricated with diameters and pitches (center-to-center distances) as small as 8 nanometers and 16 nanometers, respectively. The nanowires have high aspect ratios (up to 10(6)), and the process can be carried out multiple times to produce simple circuits of crossed nanowires with a nanowire junction density in excess of 10(11) per square centimeter. The nanowires can also be used in nanomechanical devices; a high-frequency nanomechanical resonator is demonstrated.

  View details for DOI 10.1126/science.1081940

  View details for Web of Science ID 000181988900043

  View details for PubMedID 12637672

• Ultrahigh-density nanowire lattices and circuits Science Melosh, N., A., Boukai, A., Diana, F., Gerardot, B., Badolato, A., Petroff, P., M. 2003; 300: 112-15
• Triblock copolymer syntheses of mesoporous silica with periodic 50 to 300 angstrom pores Science Zhao, D., Y., Feng, J., L., Huo, Q., S., Melosh, N., Fredrickson, G., H., Chmelka, B., F. 1998; 279: 548-552