2,179 research outputs found
Correlating AFM Probe Morphology to Image Resolution for Single-Wall Carbon Nanotube Tips
We report local-field-enhanced light emission from silicon nanocrystals close to a film of nanoporous gold. We resolve photoluminescence as the gold−Si nanocrystal separation distance is varied between 0 and 20 nm and observe a fourfold luminescence intensity enhancement concomitant with increases in the coupled silicon nanocrystal/nanoporous gold absorbance cross section and radiative decay rate. A detailed analysis of the luminescence data indicated a local-field-enhanced quantum efficiency of 58% for the Si nanocrystals coupled to the nanoporous gold layer
Switchable Imbibition in Nanoporous Gold
Spontaneous imbibition enables the elegant propelling of nano-flows because
of the dominance of capillarity at small length scales. The imbibition kinetics
are, however, solely determined by the static geometry of the porous host, the
capillarity, and the fluidity of the imbibed liquid. This makes active control
particularly challenging. Here, we show for aqueous electrolyte imbibition in
nanoporous gold that the fluid flow can be reversibly switched on and off
through electric potential control of the solid-liquid interfacial tension,
i.e. we can accelerate the imbibition front, stop it, and have it proceed at
will. Simultaneous measurements of the mass flux and the electrical current
allow us to document simple scaling laws for the imbibition kinetics, and to
explore the charge flow dynamics in the metallic nanopores. Our findings
demonstrate that the high electric conductivity along with the pathways for
ionic and/or fluid transport render nanoporous elemental gold a versatile,
accurately controllable electro-capillary pump and flow sensor for minute
amounts of liquids with exceptionally low operating voltages.Comment: 12 pages, 5 figure
Fabrication of Nanoporous Gold and Biological Applications
FABRICATION OF NANOPOROUS GOLD AND BIOLOGICAL APPLICATIONS By Badharinadh Uppalapati A Dissertation submitted in partial fulfillment of the requirements for the degree of Master of Science at Virginia Commonwealth University. Virginia Commonwealth University, 2014 Major Director: Maryanne M. Collinson, Professor, Department of Chemistry Fabrication of nanoporous gold electrodes by dealloying Au:Ag alloys has attracted much attention in sensing applications. In the first part of this work, the electrochemical response of the redox active molecule, potassium ferricyanide, in a solution of bovine serum albumin in buffer, serum or blood was studied using nanoporous gold and comparisons made to planar gold. Nanoporous gold electrodes with different surface areas and porosity were prepared by dealloying Au:Ag alloy in nitric acid for different dealloying times, specifically, 7.5, 10, 12.5, 20 minutes. Characterization was done using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), and cyclic voltammetry (CV). Using cyclic voltammetry, planar gold electrodes exposed to bovine serum albumin in buffer showed a decrease in Faradaic peak current and an increase in peak splitting for potassium ferricyanide. The time required for the peak Faradaic current to drop to one-half of its original value was 3 minutes. At nanoporous gold electrodes, however, no significant reduction in Faradaic peak current or increase in peak splitting was observed. Nanoporous gold electrodes having the smallest pore size and largest surface area showed ideal results to biofouling. These electrodes are believed to impede the mass transport of large biomolecules while allowing small redox molecules to exchange electrons effectively with the electrode. In the second part of this work, the open circuit potential (OCP) of biologic solutions (e.g., blood) was measured using nanoporous gold electrodes. Historically, the measurement of blood redox potential has been hindered due to significant fouling and surface passivation of the metal electrodes. As nanoporous gold electrodes retained electrochemical activity of redox probes like potassium ferricyanide in human serum and rabbit blood, they were used to measure the OCP of blood and plasma from various animals like pig, rabbit, rat, monkey and humans. Comparisons were made to planar gold electrodes. The OCP values at both the planar gold and nanoporous gold electrodes were different from each other and there was variability due to different constituents present in blood and plasma. The OCP of rabbit blood and crashed rabbit blood was measured and the values were found to be different from each other indicating that ORP helps in measuring the animal condition. Ascorbic acid was added to rabbit and sheep blood and OCP measured at the nanoporous electrodes. Addition of reducing agent to blood at different intervals and different concentrations showed a change in potential with concentration
3D stochastic bicontinuous microstructures: Generation, topology and elasticity
Motivated by recent experimental investigations of the mechanical behavior of nanoporous metal we explore an efficient and robust method for generating 3D representative volume elements (RVEs) with strikingly similar behavior. Our approach adopts Cahn's method of generating a Gaussian random field by taking a superposition of standing sinusoidal waves of fixed wavelength but random in direction and phase. In its theory part, our study describes closed-form expressions for how the solid volume fraction affects the binarization level, mean structure size, specific surface area, averages of mean and Gaussian curvature, and the scaled topological genus. Based on numerical studies we report on criteria for achieving representative realizations of the structure by proper choice of the number of waves and element size. We also show that periodic structures are readily created. We analyze the mechanical properties considering linear and infinitesimal elasticity and evaluate the residual anisotropy (which can be made small) and the effective values of the Young's modulus and Poisson's ratio. The numerical results are in excellent agreement with experimental findings for the variation of stiffness with solid fraction of nanoporous gold made by dealloying. We propose scaling relations that achieve naturally a perfect agreement with the numerical and experimental data. The scaling relation for the stiffness accounts for a percolation-to-cluster transition in the random field microstructure at a finite solid fraction. We propose that this transition is the origin of the previously reported anomalous compliance of nanoporous gold
Nanoporous Gold Electrodes and Their Applications in Analytical Chemistry
Nanoporous gold prepared by dealloying Au:Ag alloys has recently become an attractive material in the field of analytical chemistry. This conductive material has an open, 3D porous framework consisting of nanosized pores and ligaments with surface areas that are 10s to 100s of times larger than planar gold of an equivalent geometric area. The high surface area coupled with an open pore network makes nanoporous gold an ideal support for the development of chemical sensors. Important attributes include conductivity, high surface area, ease of preparation and modification, tunable pore size, and a bicontinuous open pore network. In this paper, the fabrication, characterization, and applications of nanoporous gold in chemical sensing are reviewed specifically as they relate to the development of immunosensors, enzyme-based biosensors, DNA sensors, Raman sensors, and small molecule sensors
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