ascorbic-acid and gold-tetrachloride--acid

Topics: Acid Phosphatase; Ascorbic Acid; Benzidines; Chlorides; Chromogenic Compounds; Colorimetry; Fluorescent Dyes; Gold Compounds; Humans; Limit of Detection; Oxidation-Reduction; Rhodamines; Smartphone; Spectrometry, Fluorescence

Ligand-free stellated gold nanoparticles (AuStNPs) with well-defined octahedral (O(h)) and icosahedral (I(h)) core symmetries were prepared using hydrogen peroxide as a reducing agent. Only three reagents: gold precursor (HAuCl4), H2O2 and NaOH were required to form colloidally and chemically stable AuStNPs with a zeta-potential between -55 and -40 mV indicative of excellent charge stabilization. The size and degree of stellation of AuStNPs can be controlled by several synthetic parameters so that the localized surface plasmon resonance (LSPR) can be varied from ca. 850 nm in near-infrared (NIR) to ca. 530 nm. In particular, AuStNP size and LSPR tuning can be conveniently accomplished by iodide variation. The size distribution of AuStNPs was improved by nucleation with ascorbic acid, and the AuStNP size and degree of branching could be readily modified using arginine. AuStNPs are advantageous for SPR sensing, as it was demonstrated in the sensitive detection of not only thiols, such as ampicillin, but also iodide with the detection limit of 3.2 pM (0.4 ng L(-1)). The reported ligand-free stable AuStNPs thus should be very useful for biodiagnostics based on SPR sensing and potentially for SERS and hyperthermia therapy.

Topics: Ascorbic Acid; Chlorides; Gold; Gold Compounds; Hydrogen Peroxide; Ligands; Metal Nanoparticles; Microscopy, Electron, Scanning; Particle Size; Sodium Hydroxide; Spectrum Analysis, Raman; Surface Plasmon Resonance

A simple and effective strategy was proposed for synthesis of AuNPs@polyaniline (AuNPs@PANI) core-shell nanocomposites. AuNPs@PANI nanocomposites were prepared by one-step chemical oxidative polymerization of aniline using chloroaurate acid as the oxidant and AuNPs as the seeds. The synthesized AuNPs@PANI nanocomposites were characterized with transmission electron microscope and UV-vis absorption spectra. Cyclic voltammetric experiments indicated that AuNPs@PANI nanocomposites showed excellent electroactivity in neutral and even alkaline solution. The obtained AuNPs@PANI nanocomposites-modified electrode was fabricated to simultaneously determine dopamine (DA) and ascorbic acid (AA) by differential pulse voltammetry. The separation between the two peak potentials of DA and AA oxidation is 236 mV. The catalytic peak currents were linearly with the concentrations of DA and AA in the range of 10-1700 and 20-1600 μM with correlation coefficients of 0.9997 and 0.9998, respectively. The detection limits for DA and AA were 5 and 8 μM, respectively.

Topics: Aniline Compounds; Ascorbic Acid; Biosensing Techniques; Chlorides; Dopamine; Electrochemistry; Electrodes; Gold Compounds; Humans; Hydrogen-Ion Concentration; Limit of Detection; Microscopy, Electron, Transmission; Nanocomposites; Oxidation-Reduction; Reproducibility of Results; Spectrophotometry

Graphene decorated with gold nanoparticles (AuNPs-β-CD-Gra) has been synthesized by in situ thermal reduction of graphene oxide and HAuCl(4) with β-cyclodextrin (β-CD) under alkaline condition. The AuNPs-β-CD-Gra product was well characterized by infrared spectroscopy, X-ray powder diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and selected area electron diffraction. This material was used to fabricate an AuNPs-β-CD-Gra-modified glassy carbon electrode (GCE) which showed excellent electro-oxidation of l-ascorbic acid (AA), dopamine (DA) and uric acid (UA) in 0.10 M NaH(2)PO(4)-HCl buffer solution (pH 2.0) by square wave voltammetry (SWV). Three well-resolved oxidation peaks of AA and DA and UA were obtained. The AuNPs-β-CD-Gra/GCE exhibits linear responses to AA, DA and UA in the ranges 30-2000, 0.5-150 and 0.5-60 μM, respectively. The detection limits (based on S/N=3 and preconcentration time=3.0 min) for AA, DA and UA are 10, 0.15 and 0.21 μM, respectively. The AuNPs-β-CD-Gra/GCE has been successfully applied to determine UA in human urine with satisfactory results. Our work provides a simple, convenient and green route to synthesize AuNPs on Gra which is potentially useful in electroanalysis.

Topics: Ascorbic Acid; beta-Cyclodextrins; Chlorides; Dopamine; Electrochemistry; Electrodes; Gold; Gold Compounds; Graphite; Green Chemistry Technology; Humans; Hydrogen-Ion Concentration; Metal Nanoparticles; Models, Molecular; Molecular Conformation; Oxidation-Reduction; Temperature; Time Factors; Uric Acid

Single strand DNA (ssDNA) was used to modify nanogold to obtain a nanogold-aptamer resonance scattering (RS) probe (NGssDNA) for Hg(2+), based on the formation of stable thymine-Hg(2+)-thymine (T-Hg(2+)-T) mismatches and aggregation of the released nanogold particles. After removing the aggregated particles by filtrate membrane, the excess NGssDNA in the filtration solution exhibit catalytic effect on the gold particle reaction between HAuCl(4) and ascorbic acid (AA) that appear as RS peak at 596nm. When Hg(2+) concentration increased, the RS intensity at 596nm decreased. The decreased intensity is linear to Hg(2+) concentration in the range of 0.00008-0.888ng/mL Hg(2+), with detection limit of 0.000034ng/mL. The nanogold-aptamer catalytic RS assay was applied to determination of Hg(2+) in water with satisfactory results.

Topics: Absorption; Aptamers, Nucleotide; Ascorbic Acid; Base Sequence; Biosensing Techniques; Catalysis; Chlorides; Circular Dichroism; DNA, Single-Stranded; Gold; Gold Compounds; Indicators and Reagents; Mercury; Metal Nanoparticles; Microscopy, Electron, Transmission; Spectrum Analysis; Thymidine

Inhibition of adenosine triphosphatase (ATPase) by chlorauric acid (Au3+) and gold sodium thiomalate (Au+) was studied in dog brain and kidney and in human kidney enzyme preparations. Au3+ indiscriminately affected ouabain-sensitive (Na+ + K+-dependent) ATPase and ouabain-insensitive (Mg2+-dependent) ATPase with concentrations for 50% inhibition (I50) approximately 10(-6) M. The I50 of Au3+ for Na+ + K+ ATPase was several-fold higher in homogenates than in microsomal fractions. The enzyme was protected by bovine serum albumin. Although Au3+ and Au+ were equipotent against Mg2+ ATPase, Au+ inhibited Na+ + K+ ATPase 2 to 3 times more effectively than did Au3+. The inhibitory action of Au3+ (but not Au+) was potentiated by ascorbic acid, suggesting reduction of Au3+ to Au+ by ascorbic acid. The fractional inhibition of Na+ + K+ ATPase by Au3+ or Au+ was not affected by changing concentrations of NaCl, KCl, MgCl2, ATP, and MgATP. Decreasing pH from 8.0 to 6.8 enhanced both Au+ and Au3+ inhibition. We conclude that gold is one of the most potent nonspecific of Na+ + K+ ATPase, with characteristics differing from other metallic inhibitors of this enzyme system.

Topics: Animals; Ascorbic Acid; Brain; Chlorides; Dogs; Gold; Gold Compounds; Gold Sodium Thiomalate; Kidney; Microsomes; Sodium-Potassium-Exchanging ATPase