Au nanospheres and nanorods for enzyme-free electrochemical biosensor applications

Au nanocrystals with different morphologies were prepared and used for enzyme-free electrochemical biosensor applications. To investigate the electrocatalytic properties of Au nanocrystals as a function on their morphologies, Au nanocrystals, Au nanospheres (NSs) on silica, Au NSs, and Au nanorods (NRs) with aspect ratios of 1:3 and 1:5, were coated on the screen printed electrodes and further measure the amperometric responses to hydrogen peroxide via three-electrode system. The electrodes modified with Au nanocrystals showed biosensing properties without any enzyme being attached or immobilized at their surface. The hydrogen peroxide detection limits of the biosensors with Au NSs, Au NRs (1:3), and Au NRs (1:5) were 6.48, 8.65, and 9.38 μM (S/N = 3), respectively. The biosensors with Au NSs, Au NRs (1:3), and Au NRs (1:5) showed the sensitivities of 11.13, 54.53, and 58.51 μA/mM, respectively. These results indicate that morphologies of Au nanocrystals significantly influence the sensitivity of the biosensors. In addition, the enzyme-free biosensors with Au nanocrystals were stable for 2 months. Au nanocrystal-based enzyme-free system, which is proposed in this study, can be used as a platform for various electrochemical biosensors.     

Localization of cell surface sites involved in fibronectin fibrillogenesis

Fibronectin binding sites on cultured human fibroblasts were localized by high voltage electron microscopy using either 5- or 18-nm colloidal gold beads (Au5 or Au18) bound to intact fibronectin, the 70-kD amino- terminal fragment of fibronectin that blocks incorporation of exogenous fibronectin into extracellular matrix, or 160-180-kD fragments of fibronectin with cell adhesion and heparin-binding activities. Binding sites for Au18-fibronectin on the cell surface were localized to specific regions along the edge of the fibroblast and on retraction fibers. Au18-fibronectin complexes at these sites were initially localized in clusters that co-aligned with intracellular microfilament bundles. With longer incubations, Au18-fibronectin complexes were arranged into long fibrillar networks on the cell surface and in the extracellular space. The appearance of Au18-fibronectin in these fibrillar networks and disappearance of clusters of Au18-fibronectin suggest that Au18-fibronectin complexes are arranged into matrix at specific regions of the cell surface. Au18-70-kD fragment complexes initially had a similar distribution to Au18-fibronectin complexes. With longer incubations, Au18-70-kD fragment complexes were found in long linear arrangements on the cell surface. Double labeling experiments using Au18-70-kD fragment and Au5-160-180-kD fragments showed that the 70-kD fragment and the 160-180-kD fragments bind to different regions of the cell.     

Ordered Hexagonal Nanoplasmonic Au Nanoparticle Arrays: AAO-Assisted Thermal Treatment Synthesis and Application as Surface-Enhanced Raman Scattering Substrates

We have reported on the synthesis of ordered hexagonal Au nanoparticle (NPs) arrays by anodic alumina oxide templates (AAO)-assisted thermal treatment. This simple process has led to the formation of an ordered hexagonal array of Au NPs on the surface of AAO. SERS properties of the ordered hexagonal Au NPs could be obtained by varying the size of Au NPs. Compared with the Au thin film on AAO, the SERS intensity of rhodamine adsorbed on the ordered hexagonal Au NPs was about 1000 times stronger. And the hexagonal Au NPs array films have had stronger Raman-enhanced signal compared to the disorder Au NPs films. Simulations according to the three-dimensional finite-difference time domain (3D-FDTD) have displayed that these electric field enhancements of the ordered hexagonal Au NPs are strongly dependent on the gap distance. Plasmonic ordered hexagonal Au NPs could provide us new platforms to realize novel optoelectronic devices.

     

巨大芽孢杆菌D01吸附金(Au3+)的研究

巨大芽孢杆菌（Ｂａｃｉｌｌｕｓ ｍｅｇａｔｅｒｉｕｍ）Ｄ０１菌体吸附ＡＵ＾３＋的最适ｐＨ值为３．０,其生物吸附作用是一种快速的过程,最初５ｍｉｎ 的吸附量可达到最大吸附量的９５％,温度不影响该吸附作用。在ｐＨ３．０和３０℃、起始金离子浓度与菌体浓度之比为３０５ｍｇ／ｇ的条件下,吸附３０ｍｉｎ,吸附率达９９．１％,吸附量为３０２．０ｍｇ／ｇ干菌体。Ｄ０１菌体能将浓度中的Ａｕ＾３＋还原成Ａｕ＾０,在细     

A Mechanistic Study of Au(III) Removal from Solution by Bacillus subtilis

Bacteria–Au interactions control the fate of Au in a variety of geologic systems. Although previous studies have determined that non-metabolizing Bacillus subtilis cells can remove Au(III) from solution via cell surface adsorption reactions, and that upon removal Au(III) is rapidly reduced to Au(I) and remains bound to the cell surface, the mechanism of Au(III) removal by B. subtilis is poorly understood. This study provides further constraints on the mechanisms responsible for Au(III) removal by B. subtilis by conducting batch Au(III) removal experiments as a function of pH and Au loading (Au:biomass ratio) using biomass with and without two different types of treatment: (1) a treatment to remove extracellular polymeric substances (EPS) from the biomass, and (2) a treatment to irreversibly block surface sulfhydryl sites from Au binding. The experimental results suggest that Au(III) removal can be attributed primarily to Au complexation with bacterial sulfhydryl sites, but that Au–amino binding is also important under some conditions. Our experiments also suggest that Au–sulfhydryl binding occurs predominantly on EPS molecules produced by B. subtilis, and that Au–amino binding is also important and is located within the bacterial cell envelope. These findings are the first to constrain the location of sulfhydryl-binding sites for B. subtilis biomass, and they are the first to demonstrate the important role played by bacterial EPS in the process of Au adsorption and reduction by bacteria.     

Effects of cooling treatment and glutaraldehyde on the morphology of Au nanostructures synthesized from chitosan

A facile approach for the synthesis of chitosan-based Au nanostructures that have interesting absorptions in the near-infrared (NIR) region is presented. The effects of cooling treatment and the cross-linking agent glutaraldehyde on the formation of Au nanostructures based on chitosan were investigated. It has been demonstrated that the size and shape, and thus the optical properties of Au nanostructures, could be modulated via cooling treatment. The optical absorption extension of these Au nanostructures in the NIR region is promising in biomedical applications. The presence of a cross-linking agent, glutaraldehyde, during synthesis accelerated the reduction of the Au precursor and favored the growth of isotropic Au nanoparticles. A possible mechanism for the change in growth modality of Au nanostructures with and without glutaraldehyde was elucidated.     

Formation of Au(III)-DNA coordinate complex by laser ablation of Au nanoparticles in solution

We discovered that an Au(III)-DNA coordinate complex, Au(III)(DNA-base)2(amine)L, are formed by laser ablation of Au nanoparticles in an aqueous solution containing DNA molecules in the presence of amines and multi-valent cations, where L represents an unknown ligand (either amine or water). Optical absorption spectrum of the solution after laser ablation exhibited a 360 nm absorption peak assined to ligand-->Au(III) charge transfer (LMCT) band of the coordinate complex. The complex is considered to be formed as follows: (1) the DNA molecules are neutralized by binding the multi-valent cations to their negatively charged phosphate groups, and adsorbed on the surface of the Au nanoparticles by a hydrophobic interaction, (2) Au(III) ions are liberated from the Au nanoparticles by laser ablation, and (3) an Au(III) ion reacts with amine and two DNA bases of a DNA molecule into an Au(III)(DNA-base)2(amine)L.     

State-sensitive monitoring of gold nanoparticle sites on titania and the interaction of the positive Au site with O2 by Au Lα1-selecting X-ray absorption fine structure

The heterogeneity of gold sites in various Au/TiO₂ catalysts was studied by means of state-sensitive Au L₃-edge X-ray absorption fine structure (XAFS) combined with high energy-resolution X-ray fluorescence spectrometry. A series of Au/TiO₂ catalysts were prepared via deposition-precipitation method on anatase-type or mesoporous (amorphous) TiO₂ added with NaOH (lower Au loading) or urea (higher Au loading). The mean Au particle size ranged between 29 and 87 Å based on high-resolution TEM (transmission electron microscope) measurements. The Au Lα₁ emission peak energy for Au/mesoporous-TiO₂ in air and Au/anatase-TiO₂ in CO (5%) corresponded to Au⁰ state. The emission peak energy for Au/anatase-TiO₂ in air shifted toward that of Au^I state. For relatively greater Au particles (average 87 Å) dispersed on mesporous TiO₂, the major valence state discriminated by Au Lα₁-selecting XANES (X-ray absorption near-edge structure) spectrum tuned to Au Lα₁ emission peak top was Au⁰, but the Au^δ− state could be successfully monitored by Au Lα₁-selecting XANES tuned to the emission energy at 9707.6 eV, of which population was relatively small compared to the case of smaller Au particles (average 29 Å) on anatase-type TiO₂. On the other hand, negative charge transfer from Au 5d to support was demonstrated in Au^δ+-state sensitive XANES tuned to 9718.3-9718.7 eV. The Au^δ+-state sensitive XANES spectra resembled theoretically generated XANES for interface Au^δ+ sites model on TiO₂ in contact with surface Ti sites. Further charge transfer was demonstrated from Au to adsorbed O₂ for Au/anatase-TiO₂ catalyst.     

Inhibitiory effects of gold(III) ions on ribonuclease and deoxyribonuclease

Inhibitory effects of gold(III) ions (Au(III)) on ribonuclease A (RNase A) and deoxyribonuclease I (DNase I) were investigated at neutral pH. RNase A was completely inhibited by 3 molar equivalents of Au(III) ions. DNase I was inhibited by 10 molar equivalents of Au(III) ions. Stoichiometric analyses suggest that Au(III) ions were coordinated to RNase A molecules. The Au(III)-inhibited RNase A and DNase I were renatured to exhibit 80% and 60% of their intrinsic activity, when the bound Au(III) ions were eliminated from the nucleases by addition of thiourea, which forms a strong complex with gold ions. This suggests that RNase A and DNase I were not oxidized to lose their activity, but reversibly complexed with Au(III) ions to lose their activity. Au(III) ions were probably considered to be bound to histidine and methionine residues in the nucleases, resulting in the inhibition of their activity. CD spectra revealed that the Au(III)-induced inhibition caused a conformational change in RNase A molecules and that the addition of thiourea induced refolding of the Au(III)-inhibited RNase A.     

Selective effects of gold (III) on parathyroid hormone-, prostaglandin E2- and guanine nucleotide-sensitive adenylate cyclase

Gold(III) (Au(III)) up to 0.25 microM increased parathyroid hormone- and prostaglandin E2-sensitive chick osteoblast adenylate cyclase activity without affecting 5'-guanylylimidodiphosphate-stimulated enzyme activity. Au(III) at 5-50 microM inhibited hormone- and nucleotide-mediated activation of adenylate cyclase. Basal adenylate cyclase activity was not influenced by Au(III) in the given concentrations. Treatment of membranes with 5'-guanylylimidodiphosphate prior to incubation with Au(III) prevented the inhibitory effect of Au(III) on adenylate cyclase. Our data suggest that Au(III) alters the response of adenylate cyclase to agonists most likely through interaction with specific sulfhydryl groups associated with the enzyme system.     

Mass synthesis of single-crystal gold nanosheets based on chitosan

Single-crystal Au nanosheets with {111} planes as basal surfaces have been synthesized on the basis of the polysaccharide chitosan. The preferential adsorption of polar groups in chitosan molecules on {111} planes of Au nuclei may account for the formation of anisotropic nanosheets. Appropriate precursor (HAuCl(4)) concentrations are vital for the formation of Au nanosheets. The Au nanostructures thus prepared exhibit interesting shape-dependent optical properties. This convenient, environmentally friendly and low-cost route may be amenable to mass production.     

Controllable anchoring of gold nanoparticles to polypyrrole nanofibers by hydrogen bonding and their application in nonenzymatic glucose sensors

An enzymeless glucose biosensor based on polypyrrole nanofibers-supporting Au nanoparticles (Au/PPyNFs) was investigated in this study. The Au/PPyNFs heterogeneous composite materials were synthesized in-situ via hydrogen bonding interactions for the assembly of polyethyleneimine (PEI) on the surface of polypyrrole nanofibers (PPyNFs). By changing the molar ratio of PPy to HAuCl(4), Au/PPyNFs with different Au loadings were obtained. The morphology and composition of Au/PPyNFs were characterized using SEM, TEM, FTIR, XRD and XPS, respectively. The hybrids exhibited a high electrocatalytic activity toward glucose oxidation, which is prerequisite for the catalysts to be applied in amperometric glucose sensors. By using the nonenzymatic glucose sensor based on Au/PPyNFs, 0.2-13mM glucose can be detected with a sensitivity of 1.003μAcm(-2)mM(-1) and a good linearity (R(2)=0.9993) between current density and glucose concentration. The proposed glucose sensor provides a promising strategy to construct fast, sensitive, and anti-interfering amperometric sensors for early diagnosis and prevention of diabetes.     

Surface Plasmon Resonance Study of Au Nanorod Structures Templated in Mesoporous Silicon

Au nanorods forming carpet-like structures have been fabricated by electrochemical methods in mesoporous silicon templates. The anodically grown monodisperse pores on Si (100) were used to cathodically grow the Au structures from complexated Au solutions. Such structures feature selective absorption of light in the visible/near infrared wavelength range that can be tuned by controlling the aspect ratio and dielectric surrounding media. In the present work, the visible light absorption of Au structures has been studied and correlated with the light absorption of ideal structures with increasing complexity. According to these simulations, the observed selective light absorption arises from the anisotropic surface plasmon resonance (SPR) of the rods and a secondary SPR of isolated Au nanoparticles adsorbed on the rods.     

Improvement of mimetic peroxidase activity of gold nanoclusters on the luminol chemiluminescence reaction by surface modification with ethanediamine

Peroxidase is a commonly used catalyst in luminol–H₂O₂ chemiluminescence (CL) reactions. Natural peroxidase has a sophisticated separation process, short shelf life and unstable activity, therefore it is important to develop peroxidases that have both high catalytic activity and good stability as alternatives to the natural enzyme. Gold nanoclusters (Au NCs) are an alternative peroxidase with catalytic activity in the luminol–H₂O₂ CL reaction. In the present study, ethanediamine was modified on the surface of Au NCs forming cationic Au NCs. The zeta potential of the cationic Au NCs maintained its positive charge when the pH of the solution was between 4 and 9. The cationic Au NCs showed higher catalytic activity in the luminol–H₂O₂ CL reaction than did unmodified Au NCs. A mechanism study showed that the better performance of cationic Au NCs may be attributed to the generation of ¹O₂ on the surface of cationic Au NCs and a positive surface charge, for better affinity to luminol. Cationic Au NC, acting as a peroxidase mimic, has much better stability than horseradish peroxidase over a wide range of temperatures. We believe that cationic Au NCs may be useful as an artificial peroxidase for a wide range of potential applications in CL and bioanalysis.     

Potential of Chilopsis linearis for gold phytomining: using XAS to determine gold reduction and nanoparticle formation within plant tissues

This study reports on the capability of the desert plant Chilopsis linearis (Cav.) Sweet (desert willow) to uptake gold (Au) from gold-enriched media at different plant-growth stages. Plants were exposed to 20, 40, 80, 160, and 320 mg Au L(-1) in agar-based growing media for 13, 18, 23, and 35 d. The Au content and oxidation state of Au in the plants were determined using an inductively coupled plasma/optical emission spectrometer (ICP/OES) and X-ray absorption spectroscopy (XAS), respectively. Gold concentrations ranging from 20 to 80 mg Au L(-1) did not significantly affect Chilopsis linearis plant growth. The concentration of gold in the plants increased as the age of the plant increased. The Au concentrations in leaves for the 20, 40, 80, and 160 mg Au L(-1) treatments were 32, 60, 62, and 179 mg Au kg(-1) dry weight mass, respectively, demonstrating the gold uptake capability of desert willow. The XAS data indicated that desert willow produced gold nanoparticles within plant tissues. Plants exposed to 160 mg Au L(-1) formed nanoparticles that averaged approximately 8, 35, and 18 A in root, stem, and leaves, respectively. It was observed that the average size of the Au nanoparticles formed by the plants is related to the total Au concentration in tissues and their location in the plant     

Effects of cyanide and dissolved oxygen concentration on biological Au recovery

The number of discarded electric devices containing traces of Au is currently increasing. It is desirable to recover this Au because of its valuable physicochemical properties. Au is usually dissolved with relatively high concentrations of cyanide, which is associated with environmental risk. Chromobacterium violaceum is able to produce and detoxify small amounts of cyanide, and may thus be able to recover Au from discarded electric devices. This study investigated the effects of cyanide and dissolved oxygen concentration on biological Au recovery. Cyanide production by C. violaceum was sufficient to dissolve Au, while maintaining a high cyanide concentration did not enhance Au dissolution. Increased oxygen concentration enhanced Au dissolution from 0.04 to 0.16 mmol/l within the test period of 70 h. Electrochemical measurement clarified this phenomenon; the rest potential of Au in the cyanide solution produced by C. violaceum increased from -400 to -200 mV, while in the sterile cyanide solution, it was constant in cyanide concentrations ranging from 0 to 1.5 mmol/l and increased in dissolved oxygen concentrations ranging from 0 to 0.25 mmol/l. Therefore, it was clarified that dissolved oxygen concentration is the main factor affecting the efficiency of cyanide leaching of gold by using bacteria.     

Systematic Study on the Self-Assembled Hexagonal Au Voids,Nano-Clusters and Nanoparticles on GaN (0001)

Au nano-clusters and nanoparticles (NPs) have been widely utilized in various electronic, optoelectronic, and bio-medical applications due to their great potentials. The size, density and configuration of Au NPs play a vital role in the performance of these devices. In this paper, we present a systematic study on the self-assembled hexagonal Au voids, nano-clusters and NPs fabricated on GaN (0001) by the variation of annealing temperature and deposition amount. At relatively low annealing temperatures between 400 and 600°C, the fabrication of hexagonal shaped Au voids and Au nano-clusters are observed and discussed based on the diffusion limited aggregation model. The size and density of voids and nano-clusters can systematically be controlled. The self-assembled Au NPs are fabricated at comparatively high temperatures from 650 to 800°C based on the Volmer-Weber growth model and also the size and density can be tuned accordingly. The results are symmetrically analyzed and discussed in conjunction with the diffusion theory and thermodynamics by utilizing AFM and SEM images, EDS maps and spectra, FFT power spectra, cross-sectional line-profiles and size and density plots.     

RNA of Australia Antigen

ALTHOUGH the exact nature of Australia (Au) antigen is not resolved, increasing evidence suggests that it is the causal agent of viral hepatitis. This supposition is based chiefly on the frequent occurrence of Au antigen in the sera of patients with viral hepatitis^1–4 and on its virus-like appearance under the electron microscope^5–7. Biochemical studies have shown that Au antigen consists largely of protein, with a minor lipid moiety^{8, 9}. So far, however, no genetic material has been detected in the Au antigen and it has been suggested that the Au antigen might be “a unique infectious particle with little or no nucleic acid”¹⁰. We wish to present evidence, however, that RNA is an essential component of Au antigen.     

Gold complexes of purine and pyrimidine nucleosides

The reactions of chloroauric acid (HAuCl₄) with inosine=ino, guanosine=guo, triacetylinosine=trino, triacetylguanosine=trguo, and cytidine=cyd were studied. Complexes of Au(III) and Au(I) with these nucleosides have been isolated from reactions at different pH values in aqueous and in methanolic solutions. The Au(I) complexes were obtained by reducing Au(III) with 1-ascorbic acid in aqueous solutions. All the isolated complexes were characterized by elemental analyses, conductivity measurements, IR, ¹H nmr, and esr spectra. The Au(III) complexes correspond to the general formulae [Au(nucl)₂Cl₂] Cl, Au(nucl)Cl₃, and Au(nucl-H⁺)Cl₂, while the Au(I) complexes are of the Au(nucl)₂Cl type, where nucl represents the above nucleosides. In the complex with the composition [AucydCl₂]₂ that was isolated from aqueous solutions, the Au atom is believed to be in the (II) oxidation state.Possible structures for all the isolated complexes based on the experimental data are proposed and discussed.