Gold Nanochannel Research Articles

Gold nanochannels oxidation by confined water.

Confined and interstitial water has a key role in several chemical, physical and biological processes. It is remarkable that many aspects of water behavior in this regime (e.g., chemical reactivity) remain obscure and unaddressed. In particular for gold surfaces, results from simulations indicated that the first wetting layer would present hydrophilic behavior in contrast to the overall hydrophobic character of the bulk water on this surface. In the present work we investigate the properties of confined water on Au 〈111〉 nanochannels. Our findings, based on a large set of morphological, structural and spectroscopic experimental data and ab initio computer simulations, strongly support the hypothesis of hydrophilicity of the first wetting layer of the Au 〈111〉 surface. A unique oxidation process was also observed in the nanochannels driven by confined water. Our findings indicated that the oxidation product is Au(OH)3. Therefore, the Au surface reactivity against confined water needs to be considered for nanoscopic applications such as, e.g., catalysis in fine chemicals, pharmaceuticals, and the food industry green processes.

Study of the enantioselectivity and recognition mechanism of sulfhydryl-compound-functionalized gold nanochannel membranes.

Two new chiral membranes were prepared by modification of gold nanochannel membranes with D-penicillamine and N-acetyl-L-cysteine and were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy. The effects of key factors such as the gold deposition time, the pH, and the concentration of sodium dihydrogen phosphate on the separation factor are discussed. Chiral resolution of amino acid enantiomers by the chiral membranes was investigated. The experimental results show that the D-penicillamine-modified membrane has good enantioselectivity toward tyrosine and phenylalanine enantiomers, whereas the N-acetyl-L-cysteine-modified membrane has good enantioselectivity toward tyrosine and tryptophan enantiomers. Furthermore, the chiral recognition mechanism was studied by density functional theory. The calculation results indicate that the basic chiral recognition system of D-penicillamine complexes involves only one chiral selector and one selected enantiomer, whereas that of N-acetyl-L-cysteine complexes involves two chiral selectors and one selected enantiomer. Finally, the NH3+ group of D-penicillamine is proved to play an important role in enhancing interactions between complexes and improving enantioselectivity. Graphical abstract Enantioselective interactions between amino acid enantiomers and sulfhydryl-compound-functionalized gold nanochannel membranes.

Enantioselective permeations of amino acids through L-proline-modified gold nanochannel membrane: an experimental and theoretical study.

L-Proline-modified gold nanochannel membrane (L-Pro-GNM) was prepared and applied for the enantioselective permeations of amino acid enantiomers including tyrosine (Tyr), tryptophan (Trp) and phenylalanine (Phe). Experimental results show that L-Pro-GNM has enantioselectivities for Tyr and Phe enantiomers. Furthermore, the chiral recognition mechanism was studied by density functional theory (DFT) and reduced density gradient (RDG). DFT computational results illustrate that the fundamental chiral recognition system contains two chiral selectors and one selectand, which can be used to evaluate the enantioselective efficiencies of other chiral compounds and the enantioselective ability of other potential amino acid-modified GNM. Finally, graphs obtained by RDG using Multiwfn show helpful visual interactions between the chiral selector and selectand. Results indicate that the electrostatic interaction and hydrogen bonding are responsible for the binding of the chiral selector and selectand, and the larger binding energy shows larger van der Waals interactions.

Temperature profiles and heat fluxes observed in molecular dynamics simulations of force-driven liquid flows.

This paper concentrates on the unconventional temperature profiles and heat fluxes observed in non-equilibrium molecular dynamics (MD) simulations of force-driven liquid flows in nano-channels. Using MD simulations of liquid argon flows in gold nano-channels, we investigate the manifestation of the first law of thermodynamics for the MD system, and compare it with that of the continuum fluid mechanics. While the energy equation for the continuum system results in heat conduction determined by viscous heating, the first law of thermodynamics in the MD system includes an additional slip-heating term. Interaction strength between argon and gold molecules is varied in order to investigate the effects of slip-velocity on the slip-heating term and the resulting temperature profiles. Heat fluxes and temperature profiles from "continuum", "continuum augmented with slip-heating", and "heat conduction due to the power input by the driving force" are modeled and compared with the MD results. The continuum model can neither predict the heat fluxes nor the temperature profiles from MD simulations. While the continuum model augmented with slip-heating matches the MD heat fluxes, the resulting temperature profiles do not agree with the MD predictions. Overall the analytical model based on "heat conduction due to power input by the driving force" matches the heat fluxes from MD simulations, while the temperature profiles match MD predictions using an effective thermal conductivity that is about 70% of the thermodynamic value. Using different liquid-wall pairs affects the slip velocity, temperature jump, and the resulting thermal conductivity of the fluid, but results in similar physical observations. The inability of the MD method in mimicking continuum fluid mechanics in energy transport for force-driven liquid flows is scale independent, and it is more likely a numerical artifact.

A phenomenological continuum model for force-driven nano-channel liquid flows.

A phenomenological continuum model is developed using systematic molecular dynamics (MD) simulations of force-driven liquid argon flows confined in gold nano-channels at a fixed thermodynamic state. Well known density layering near the walls leads to the definition of an effective channel height and a density deficit parameter. While the former defines the slip-plane, the latter parameter relates channel averaged density with the desired thermodynamic state value. Definitions of these new parameters require a single MD simulation performed for a specific liquid-solid pair at the desired thermodynamic state and used for calibration of model parameters. Combined with our observations of constant slip-length and kinematic viscosity, the model accurately predicts the velocity distribution and volumetric and mass flow rates for force-driven liquid flows in different height nano-channels. Model is verified for liquid argon flow at distinct thermodynamic states and using various argon-gold interaction strengths. Further verification is performed for water flow in silica and gold nano-channels, exhibiting slip lengths of 1.2 nm and 15.5 nm, respectively. Excellent agreements between the model and the MD simulations are reported for channel heights as small as 3 nm for various liquid-solid pairs.

Scale effects in nano-channel liquid flows

Force-driven liquid argon flows both in nanoscale periodic domains and in gold nano-channels are simulated using non-equilibrium molecular dynamics to investigate the scale and wall force field effects. We examined variations in liquid density, viscosity, velocity profile, slip length, shear stress and mass flow rate in different sized periodic domains and nano-channels at a fixed thermodynamic state. In the absence of walls, liquid argon obeys Newton’s law of viscosity with the desired absolute viscosity in domains as small as 4 molecular diameters in height. Results prove that deviations from continuum solution are solely due to wall effects. Simulations in nano-channels with heights varying from 3.26 to 36 nm exhibit parabolic velocity profiles with constant slip length modeled by Navier-type slip boundary condition. Both channel averaged density and “apparent viscosity” decrease with reduced channel height, which has competing effects in determination of the mass flow rate. Density layering and wall force field induce deviations from Newton’s law of viscosity in the near-wall region, while constant “apparent viscosity” with the deformation rate from a parabolic velocity profile successfully predicts shear stress in the bulk flow region.

Calculation of Spin Conduction Matrix in Spin Circuit Considering Nano-Magnetic Nodes and Copper Nano-Channel

In this work, we intend to calculate spin conduction matrixes of T-shaped spin circuits' branches. Also we investigate simultaneously effects of gold nano-channel length and cross section area variations on its non-zero elements. Our findings show that G 11 and G 22 elements of series branches increase with simultaneously channel length reduction and channel cross section area grow up. For spin flip branches, G 22 element decreases with simultaneously nano-channel length and cross section area reduction. We choose copper metal as nano-channel because of its high conductance and lattice constant.

Aptamer-Modified Gold Nanochannels Membrane for Separation of β-Estradiol and Estrone

Abstract In the present work, a new method for the separation of β-estradiol and estrone by the modified gold nanochannels membrane was described. The gold nanochannels were prepared by chemical deposition of gold on polycarbonate templates membrane. The morphology of the nanochannels, characterized by field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM), showed that smooth and uniform Au nanochannels were produced. After being modified with aptamer on the nanochannels membranes using a molecular self-assembly method, the nanochannels membranes facilitated the transport of β-estradiol through the membranes while the estrone was not easy to permeate. The transport behaviours of β-estradiol and estrone through the gold nanochannels modified with aptamer of β-estradiol were investigated. The results showed that the nanochannels membrane modified with β-estradiol aptamer could be used to separate β-estradiol and estrone on the basis of unique selectivity. A separation efficiency of 1.75 was obtained when the nanochannels had a pore size of 20 nm in the medium pH from 6.0 to 8.0.

Study on transportation of phenol through a nanotubule membrane

Gold nanochannels were prepared by plating electrolessly gold within the pores of polycarbonate lter membranes (PCTMs). These PCTMs with cylindrical Au nanotubules of uniform radius and high density can be used as a convenient model system to investigate the mechanism of particle transport through nanotubules. The transport properties of phenol through a modied Au nanotubule membrane were studied. The permeate ux of phenol transport through the nanotubule membrane can be spatially and temporally manipulated by controlling the magnitude and direction of the current applied across the separation cell, and the electroosmotic ow (EOF) was investigated by measuring the ux of phenol across the PCTM. The current values and modication of nanotubules aected the EOF generated inside the nanotubules. The permeation ux of phenol through the nanotubule membrane can be easily changed by modifying the Au nanotubules with Cl or L-cysteine, and changing the direction of the applied current and the pH of the buer solution used in mass transport experiments.

Study of transportation of atrazine and paraquat through nanochannels

The transportation of paraquat and atrazine through the modified gold nanochannels polycarbonate track etched (PCTE) membrane was described. The gold nanochannels can be electrolessly plated within the pores of PCTE membranes. The gold nanochannels were hydrophobic because of modification of thiol (HSC18H37). They can forbid paraquat and allow atrazine to transport through the membranes. However, these hydrophobic membranes can be switched from an “off” state (no or lower ion-current through the membrane) to an “on” state (higher ion-current) due to the presence of some surfactants. The effects of different surfactants, including cationic surfactant such as C16H29 (CH3)3NH4Br, nonionic surfactant like emulsifier OP, on the transport properties of paraquat through the membrane were investigated. It is found that for some alkyl surfactants with a 12-carbon chain length can switch the membrane to the on state even if their concentrations were lower than critical micelle concentrations. Specially, for a 10-carbon chain alkyl surfactant, 1-decanesulfonic acid sodium has the same function of switching the membrane to the on state as long as its concentration is high enough. But other chemical substances, regardless of cation, anion or molecule, cannot switch the membrane.

Cold-welding fabrication of highly ordered gold nanochannel monolayers in aqueous medium

Herein, we demonstrate that galvanic replacement reaction over aligned Ag nanowire arrays can be employed as a simple and powerful cold-welding technique for large-scale fabrication of highly ordered Au nanochannel monolayers.