Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:6.2.1.1 (ACS)
 78,556 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Ultrathin silicon-on-insulator, composed of a crystalline sheet of silicon bounded by native oxide and a buried oxide layer, is extremely resistive because of charge trapping at the interfaces between the sheet of silicon and the oxide. After chemical modification of the top surface with hydrofluoric acid (HF), the sheet resistance drops to values below what is expected based on bulk doping alone. We explain this behavior in terms of surface-induced band structure changes combined with the effective isolation from bulk properties created by crystal thinness.
ACS Nano 2009 Jul 28
PMID:Influence of surface chemical modification on charge transport properties in ultrathin silicon membranes. 1949 33

We integrate microtubule (MT)-resistant self-assembled monolayers (SAMs) with lithographically patterned electrodes to control MTs in a cell-free environment. Formed through a facile, one-step assembly method, the poly(ethylene glycol) trimethoxysilane SAM prevents MT adsorption on both silicon substrates and Au microstructures without casein. We characterize the SAM using ellipsometry, X-ray photoelectron spectroscopy, and atomic force microscopy and compare it with other MT passivation techniques. The SAM retains its passivating ability when used as a substrate for electron beam lithography, a key feature that allows us to pattern microtubules on lithographically defined Au structures. Moreover, by combining the SAM-passivated Au microelectrodes and DC electrophoresis, we demonstrate reversible trapping of MTs as well as capture and alignment of individual MTs.
ACS Nano 2009 Jul 28
PMID:Surface manipulation of microtubules using self-assembled monolayers and electrophoresis. 1951 95

Ultrathin AlN/GaN crystalline porous freestanding nanomembranes are fabricated on Si(111) by selective silicon etching, and self-assembled into various geometries such as tubes, spirals, and curved sheets. Nanopores with sizes from several to tens of nanometers are produced in nanomembranes of 20-35 nm nominal thickness, caused by the island growth of AlN on Si(111). No crystal-orientation dependence is observed while releasing the AlN/GaN nanomembranes from the Si substrate indicating that the driving stress mainly originates from the zipping effect among islands during growth. Competition between different relaxation mechanisms is experimentally revealed for different nanomembrane geometries and well-described by numerical calculations. The cathodoluminescence emission from GaN nanomembranes reveals a weak peak close to the GaN bandgap, which is dramatically enhanced by electron irradiation.
ACS Nano 2009 Jul 28
PMID:Fabrication, self-assembly, and properties of ultrathin AlN/GaN porous crystalline nanomembranes: tubes, spirals, and curved sheets. 1955 86

One of the most challenging but potentially rewarding goals in nanoscience is the ability to direct the assembly of nanoscale materials into functional architectures with high yields, minimal steps, and inexpensive procedures. Despite their unique physical properties, the inherent difficulties of engineering wafer-level arrays of useful devices from nanoscale materials in a cost-effective manner have provided serious roadblocks toward technological impact. To address nanoscale features while still maintaining low fabrication costs, we demonstrate here an inexpensive printing method that enables repeated patterning of large-area arrays of nanoscale materials. DNA strands were patterned over 4 mm areas with 50 nm resolution by a soft-lithographic subtraction printing process, and DNA hybridization was used to direct the assembly of sub-20 nm materials to create highly ordered two-dimensional nanoparticle arrays. The entire printing and assembly process was accomplished in as few as three fabrication steps and required only a single lithographically templated silicon master that could be used repeatedly. The low-cost procedures developed to generate nanoscale DNA patterns can be easily extended toward roll-to-roll assembly of nanoscale materials with sub-50 nm resolution and fidelity.
ACS Nano 2009 Aug 25
PMID:50 nm DNA nanoarrays generated from uniform oligonucleotide films. 1960 37

Thin (0.5 to 1 microm) layers of nonaligned or quasi-aligned hollow ZnO fibers were prepared by sputtering ZnO onto sacrificial templates comprising polyvinyl-acetate (PVAc) fibers deposited by electrospinning on silicon or alumina substrates. Subsequently, the ZnO/PVAc composite fibers were calcined to remove the organic components and crystallize the ZnO overlayer, resulting in hollow fibers comprising nanocrystalline ZnO shells with an average grain size of 23 nm. The inner diameter of the hollow fibers ranged between 100 and 400 nm and their wall thickness varied from 100 to 40 nm from top to bottom. The electronic transport and gas sensing properties were examined using DC conductivity and AC impedance spectroscopy measurements under exposure to residual concentrations (2-10 ppm) of NO(2) in air at elevated temperatures (200-400 degrees C). The inner and outer surface regions of the hollow ZnO fibers were depleted of mobile charge carriers, presumably due to electron localization at O(-) adions, constricting the current to flow through their less resistive cores. The overall impedance comprised interfacial and bulk contributions. Both contributions increased upon exposure to electronegative gases such as NO(2) but the bulk contribution was more sensitive than the interfacial one. The hollow ZnO fibers were much more sensitive compared to reference ZnO thin film specimens, displaying even larger sensitivity enhancement than the 2-fold increase in their surface to volume ratio. The quasi-aligned fibers were more sensitive than their nonaligned counterparts.
ACS Nano 2009 Sep 22
PMID:Hollow ZnO nanofibers fabricated using electrospun polymer templates and their electronic transport properties. 1968 4

This work focuses on the synthesis and interfacial characterization of gold nanostructures on silicon surfaces, including Si(111), Si(100), and Si nanowires. The synthetic approach uses galvanic displacement, a type of electroless deposition that takes place in an efficient manner under aqueous, room-temperature conditions. The case of gold-on-silicon has been widely studied and used for several applications and yet, a number of important, fundamental questions remain as to the nature of the interface. Some studies are suggestive of heteroepitaxial growth of gold on the silicon surface, whereas others point to the existence of a silicon-gold intermetallic sandwiched between the metallic gold and the underlying silicon substrate. Through detailed high resolution transmission electron microscopy (TEM), combined with selected area electron diffraction (SAED) and nanobeam diffraction (NBD), heteroepitaxial gold that is grown by galvanic displacement is confirmed on both Si(100) and Si(111), as well as silicon nanowires. The coincident site lattice (CSL) of gold-on-silicon results in a very small 0.2% lattice mismatch due to the coincidence of four gold lattices to three of silicon. The presence of gold-silicon intermetallics is suggested by the appearance of additional spots in the electron diffraction data. The gold-silicon interfaces appear heterogeneous with distinct areas of heteroepitaxial gold on silicon, and others, less well-defined, where intermetallics may reside. The high resolution cross-sectional TEM images reveal a roughened silicon interface under these aqueous galvanic displacement conditions, which most likely promotes nucleation of metallic gold islands that merge over time: a Volmer-Weber growth mechanism in the initial stages.
ACS Nano 2009 Sep 22
PMID:Heteroepitaxial growth of gold nanostructures on silicon by galvanic displacement. 1971 82

Cathodoluminescence spectroscopy has been performed on silver nanoparticles in a scanning electron microscopy setup. Peaks appearing in the visible range for particles fabricated on silicon substrate are shown to arrive from excitation of out-of-plane eigenmodes by the electron beam. Monochromatic emission maps have been shown to resolve spatial field variation of resonant plasmon mode on length scale smaller than 25 nm. Finite-difference time-domain numerical simulations are performed for both the cases of light excitation and electron excitation. The results of radiative emission under electron excitation show an excellent agreement with experiments. A complete vectorial description of induced field is given, which complements the information obtained from experiments.
ACS Nano 2009 Oct 27
PMID:Imaging of plasmonic modes of silver nanoparticles using high-resolution cathodoluminescence spectroscopy. 1973 3

Weak molecular interactions drive processes at the core of living systems, such as enzyme-substrate interactions, receptor-ligand binding, and nucleic acid replication. Single-molecule force spectroscopy is a remarkable tool for revealing molecular scale energy landscapes of noncovalent bonds, by exerting a mechanical force directly on an individual molecular complex and tracking its survival as a function of time and applied force. In principle, force spectroscopy methods can also be used for highly specific molecular recognition assays, by directly characterizing the strength of bonds between probe and target molecules. However, complexity and low throughput of conventional force spectroscopy techniques render such biosensing applications impractical. Here we demonstrate a straightforward single-molecule approach, suitable for both biophysical studies and molecular recognition assays, in which a approximately 3 nm silicon nitride nanopore is used to determine the bond lifetime spectrum of the biotin-neutravidin complex. Thousands of individual molecular complexes are captured and dissociated in the solid-state nanopore under constant applied forces, ranging from 400 to 900 mV, allowing us to extract the location of the energy barrier that governs the interaction, mapped at Deltax approximately 0.5 nm. These results highlight the capacity of a solid-state nanopore to detect and characterize intermolecular interactions and demonstrate how this could be applied to rapid, highly specific molecular detection assays.
ACS Nano 2009 Oct 27
PMID:Single-molecule bonds characterized by solid-state nanopore force spectroscopy. 1975 Oct 64

Local probe oxidation experiments by conductive AFM have been performed on a hexadecyl monolayer and a N-hydroxysuccinimide (NHS)-ester-functionalized undecyl (NHS-UA) monolayer assembled on hydrogen-terminated (i.e., unoxidized) silicon. The oxidation conditions for the mild oxidation of the top terminal groups of monolayers and the deep oxidation of the underlying silicon into silicon oxide were investigated. The results show that the bias threshold for the AFM tip-induced oxidation of the top groups of monolayers on oxide-free silicon can be reduced by 2 V for the methyl-terminated hexadecyl monolayer and even by 3.5 V for the active NHS-ester-terminated undecyl monolayer, in comparison to a methyl-terminated octadecyl trichlorosilane (OTS) monolayer on oxidized silicon. Upon such local mild oxidation, the active NHS ester group of the NHS-UA monolayer is selectively cleaved off to generate carboxyl-containing monolayer nanopatterns, opening further possibilities for subsequent patterned multifunctionalization.
ACS Nano 2009 Oct 27
PMID:Local probe oxidation of self-assembled monolayers on hydrogen-terminated silicon. 1975 33

We observe pore formation with diameters in the 10 nm range in silicon when it is covered with gold particles. This pore etching occurs when the sample is put in 5 wt % hydrofluoric acid (HF) solution for a few minutes. The pores form along the 100 direction, which is also the preferred direction of macro- and mesopores electrochemically etched into silicon. No etching occurs if the dissolved oxygen is removed from the aqueous HF solution or the gold is removed from the silicon surface. This leads to the assumption that the dissolved oxygen acts as an oxidant as in the case of stain etching with gold as cathodic material. A tentative model is suggested to explain why all of the observed nanopores have roughly the same diameter of about 10 nm. These pores can occur for inhomogeneously gold-covered planar silicon surfaces but also in MBE (molecular beam epitaxy) grown silicon nanowires since these nanowires are covered unintentionally with gold nanoclusters at their cylindrical surface.
ACS Nano 2009 Oct 27
PMID:Formation of straight 10 nm diameter silicon nanopores in gold decorated silicon. 1976 Nov 94


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>