Two Types of Potential Oscillation During the Reduction of Dichromate on Gold Electrode in H2SO4 Solution

Two different types of potential oscillations have been identified for the first time during dichromate reduction on a gold electrode in a solution of dilute sulfuric acid. One occurs before hydrogen evolution due to the formation and dissolution of passivating films of low-valence chromium oxides, and the other generates, accompanying periodic hydrogen evolution, from the coupling of electrochemical reactions with diffusive and convective mass transport. More interestingly, these two types of oscillations correspond to two crossing loops in the cyclic voltammogram （CV）. Such a relation of oscillations with crossed CVs will provide a new way to find electrochemical oscillatory systems systematically and rapidly.

Electrochemical Behavior and Determination of Trifluoperazine at Decanethiol Self-Assembled Monolayer Modified Gold Electrodes

The electrochemical behavior of trifluoperazine at decanethiol self-assembledmonolayer (SAM) modified gold electrodes (i. e. C_(10) H_(21) SH/Au) has been studied,Trifluoperazine can effectively accumulate on C_(10) H_(21) SH/Au electrodes and generate asensitive anodic peak at about 0.63 V (vs. SCE) in 0.05 mol/L pH 9.4 Na_2 B_4 O_7 buffer solution.Under the selected conditions, the anodic peak current was linear to trifluoperazine concentrationin the range of 5.0 X 10^(-7)-3.O X 10^(-3) mol/Lwith correlation coefficient of 0.997, thedetection limit was 3.0 X 10^(-5) mol/L. This method was applied to the determination oftrifluoperazine in drug samples and the recovery was 97.3%-104.0% It was found that sodium dodecylsulfate (SDS) could make the anodic peak current increase. In the presence of SDS, the peak at about0.63 V turned into two peaks, resulting from the change of the electrochemical mechanism.

Direct Electrochemical Evidence of the Dissociation and Adsorption Behavior of Acetonitrile at Gold Electrodes by Ultrafast Voltammetry

Ultrafast cyclic voltammetry was used to study the redox behavior of a gold electrode in acetonitrile. The direct electrochemical evidence of the dissociation and adsorption behavior of acetonitrile at gold electrodes was found. It could be stated that two consecutive redox paths are involved, each with a special adsorption state acting as the reaction intermediate. The mean value, obtained of the electron-transfer rate constant of the second path, was 1.3 × 10^5 s^-1 with a standard deviation of 0.24 × 10^5 s^-1.

Anion Adsorption on an Au Colloid Monolayer Based Cysteamine-Modified Gold Electrode

Anion adsorption behavior on Au colloid surface was investigated in virture of depositing monolayers of Au colloid on the self-assembled monolayers of cysteamine on a gold electrode. Po- tential-dependent anion adsorption-desorption waves via the nonfaradaic current were obtained by means of cyclic voltammetry at Au coltoid-modified gold electrodes in the potential range of -2 00-600 mV. The adsorption sequence in the order of adsorption peak potentials (Epa) is OH- >citrate3 ->H2PO4- >Cl->SO42->ClO4->NO3-. Among them, citrate3- exhibited an en- tirely irreversible adsorption. A rise in temperature can increase the rates of adsorption-desorp- tion and improve the reversibility of the adsorption-desorption of Cl-, SO42-, ClO4-, NO3- and H2PO-4. The adsorption peak potentials shifted more negatively for Ca. 63 mV as the anion con- centrations were increased by a decade factor. The change of pH from 7 to 1 slightly affected the adsorption peak potentials of Cl- and NO3-. Au colloids with a smaller size (16 nm) gave rise to a better reversibility of the adsorption-desorption process and lower adsorption currents. The ex- perimental results of citrate ions adsorption on Au colloid surface show that Au colloids with a smaller size prepared by sodium citrate method exhibited a higher stability in the solution in com- parison to those with larger sizes because of its higher ratio of charge/mass. In other words, the smaller gold nanoparticles are covered with citrate ions monolayer that can also be formed at larg- er gold nanoparticles by means of electrochemical scan.

ELECTROCHEMISTRY OF OI-μ-OXO-DIMANGANESE COMPLEX AT THIOURACIL MODIFIED GOLD ELECTRODE

The electrochemistry of di-μ-oxo-dimanganese complex was investigated. It was found that no redox peak was observed in the cyclic voltammogram (CV) of the complex at the bare gold electrode, but at thiouracil-modified gold electrode, a pair of redox peaks were observed showing that thiouracil can promote the proton-coupled electron transfer reaction of the complex.

PROMOTION EFFECT OF PYRIDINE FOR THE DIRECT ELECTROCHEMISTRY OF CYTOCHROME C AT GOLD ELECTRODES

It was found for the first time that the compounds with only one functional group, such as pyridine, can show the promotion effect for the electrochemical reaction of cytochrome C at gold electrodes.

A Gold Electrode QCM Study on the Self-Assembling Process of Thioglycollic Acid in Aqueous Solution

In this letter, the self-assembling process of thioglycollic acid on gold in aqueous solutions was studied by QCM technique. Frequency information suggests bilayer or multilayer adsorbate formation in 0.5 mol/L HCl solution but only monolayer one in 0.5 mol/L KOH solution. This phenomenon is explained by hydrogen bond effect.

A comprehensive first-principle study of borophene-based nano gas sensor with gold electrodes

Using density functional theory combined with nonequilibrium Green’s function method,the transport properties of borophene-based nano gas sensors with gold electrodes are calculated,and comprehensive understandings regarding the effects of gas molecules,MoS2 substrate and gold electrodes to the transport properties of borophene are made.Results show that borophene-based sensors can be used to detect and distinguish CO,NO,NO2 and NH3 gas molecules,MoS2 substrate leads to a nonlinear behavior on the current-voltage characteristic,and gold electrodes provide charges to borophene and form a potential barrier,which reduced the current values compared to the current of the systems without gold electrodes.Our studies not only provide useful information on the computationally design of borophene-based gas sensors,but also help understand the transport behaviors and underlying physics of 2D metallic materials with metal electrodes.

Underpotential Deposition Study and Determination of Bismuth on Gold Electrode by Using Voltammetry

The cyclic voltammetry (CV) and the semidifferential anodic stripping voltammetry (SdASV) were used for investigation of bismuth(III) underpotential deposition (UPD) on gold electrode. Based on the excellent electrochemical properties of Au/Bi UPD system, a new method for determining bismuth(III) was established. A solution of 0.1 mol/L HNO 3 was selected as the supporting electrolyte. Factors affecting the Bi(III) UPD and stripping steps were investigated and an optimized analytical procedure was developed. The calibration plots for Bi(III) concentration in the range 1.25×10 -8 -1.0×10 -7 mol/L were obtained. The detection limit, calculated as three times the standard deviation of the analytical signal of 8.3×10 -8 mol/L for a 90 s electrodeposition at 0.00 V (while the solution magnetically stirred at a speed of 300 rpm), was 7.5×10 -9 mol/ L. For 8 successive determinations of 1.25×10 -7 mol/L Bi(III), the obtained RSD (relative standard deviation) was 0.4%. The developed method was applied to bismuth determining in medicine and urine samples. The analytical results were compared with that of atomic emission spectrometry (AES) method.

Studies on the Gold-Coated Electrode with Grid

Introduction Thin-layer spectroelectrochemical method has many unique advantages, therefore this method has been widely applied and developed. Recently light transparent thinlayer spectroelectrochemical cells with various types of structures have been reported at home and abroad with gold or platinum minigrids as the working electrode in most of

Reaction of erythromycin with dissolved oxygen on gold nanoparticle-modified glassy carbon electrodes

Cyclic voltammetry was used to investigate the reaction of erythromycin （EM） with dissolved oxygen on gold nanopartiele-modified electrodes prepared via electrodeposition. A well-defined reduction peak at -0.420 V and a reoxidation peak at -0.055 V were observed. With the addition of EM into the NaOH solution containing dissolved oxygen, the oxidation peak at -0.055 V was still indiscernible. However, a new oxidation peak at 0.200 V appeared, which suggests the interaction between EM and dissolved oxygen. Therefore, this method can be used for the analysis of EM in tablets. The present method is simple, reproducible, and does not require complex analytical instruments.

Preparation and Characterization of Gold Thin Film Electrode Modified by Microbe

A novel method based on microbe modification has been employed to prepare gold thin film electrode. The preparation method is simple and the electrode obtained is stable and very sensitive in determining heavy metal ions. The quantitation limit of Cu2+ is 0.05 ng/mL.

In Situ FTIR Spectroscopic Study of Electrochemical Adsorption of Phosphate Ions on Gold

Infrared reflection-absorption spectra for primary, secondary and tertiary orthophosphate anions on a gold electrode in aqueous solution were studied by in situ FTIR spectroscopy. The spectra show that H2PO4- , HPO ions do not interact with the electrode surface as strong as PO do. According to the surface selection rule, we deduce the modes of adsorption of these anions on the electrode from these spectra. The experiment also confirms the affection to adsorption of ion on the electrode due to ion-migration into thin-layer cavity.

The Determination of Iodide Based on a Flow-injection Coupling Irreversible Biamperometry

A novel flow-injection irreversible biamperometric method is described for the direct determination of iodide. The method is based on electrochemical oxidation of iodide at the gold electrode and the reduction of permanganate at the platinum electrode to form an irreversible biamperometric detection system. Under the applied potential difference of 0 V, in the 0.05 mol/L sulfuric acid, iodidecan be determined over the range 4.00×10^-7-1.00×10^-5 mol/L with a sampling frequency of 120 samples per hour. The detection limit for I- is 3.0×10^-7 mol/L and the RSD for 40 replicate determinations of 4.0×10^-5 mol/L potassium iodide is 1.68%. The new method was applied to the analysis of iodide in table salt with satisfactory results.

Attachment of tyrosinase on mixed self-assembled monolayers for the construction of electrochemical biosensor

A mixed self-assembled monolayers （SAMs） of thioctic acid （T-COOH） and thioctic acid amide （T-NH2） were used to immobilize tyrosinase for fabricating biosensor. The results showed that the mixed SAMs prepared from solution at the ratio of 1：4 provided an excellent microenvironment for enzymatic reaction between tyrosinase and substrate. The biosensor exhibited a fast response and high sensitivity for sensing substrate.

The growth of Staphylococcus aureus and Escherichia coli in low-direct current electric fields

Electrical potentials up to 800 mV can be observed between different metallic dental restorations. These potentials produce fields in the mouth that may interfere with microbial communities. The present study focuses on the impact of different electric field strengths （EFS） on the growth of Staphylococcus aureus （ATCC 25923） and Escherichia coil （ATCC 25922） in vitro. Cultures of S. aureus and E. coil in fluid and gel medium were exposed to different EFS. Effects were determined by calculation of viable counts and measurement of inhibition zones. In gel medium, anodic inhibition zones for S. aureuswere larger than those for E. coliat all field strength levels. In fluid medium, the maximum decrease in the viable count of S. aureus cells was at 10 V.m-1. Field-treated S. aureus cells presented ruptured cell walls and disintegrated cytoplasm. Conclusively, S. aureus is more sensitive to increasing electric field strength than E. coll.

Determination of levodopa in pharmaceutical preparations by irreversible biamperometry

Based on the electrocatalytic oxidation of levodopa at gold electrode and the reduction of permanganate at platinum electrode, a novel flow injection irreversible biamperometric method is developed for the determination of levodopa under the potential difference of 0 V imposed between two electrodes. In H2SO4 solution, the linear relationships between currents and the concentrations of levodopa are obtained in the range from 0.04 mg/L to 20 mg/L with the detection limit of 0.012 mg/L. The proposed method is applied to the determination of levodopa in pharmaceutical preparations.

Electrochemical Study of Hypophosphite

Electrochemical behavior of hypophosphite was studied with cyclic voltammogram in acidic solution(pH = 4.6) at 80℃. Two anodic peaks were observed on gold electrode at - 0.44V and - 0.59 V (SCE),respectively, and no corresponding cathodic peaks were obtained. The one at - 0.44 V wits ascribed to the oxidation oftautomeric form of hypophosphite, the other at - 0.59 V was due to the oxidation of absorbed form of hypophosphite. The two oxidation reactions were believed to be the electron source of nickel ion reduction in electrolessnickel processes.

Cucurbit[6]uril functionalized gold nanoparticles and electrode for the detection of metformin drug

Based on the host-guest molecular recognition capability of cucurbit[6]uril(CB[6])modified on the gold surface,sensitive spectrophotometric and electrochemical methods for the detection of metformin(MET)have been developed.The molecular recognition between cucurbit[7]uril(CB[7])or CB[6]and MET is initially demonstrated and the related recognition mechanism is further deliberated.First,CB[6]-modified gold nanoparticles(AuNPs/CB[6])were synthesized and then characterized by ultraviolet visible light spectrum(UV–vis)and transmission electron microscopy(TEM).The aggregation of Au NPs/CB[6]prompted by MET triggered changes of color and the absorption spectrum,that explored for the visual identification and spectrophotometric determination of MET.Under the optimized detection conditions,the UV–vis spectrometry had a good linear relationship in the range of 6–700μmol/L,and the detection limit was 2μmol/L.In addition,a single-layer CB[6]-modified gold electrode(GE-CB[6])detection system for MET was constructed.As the concentration of MET in the solution continues to increase,the charge transfer resistance(Rct)in the Nyquist diagram of the electrochemical impedance method(EIS)continues to increase.In the concentration range from 10 pmol/L to 20 nmol/L,the logarithm of the MET concentration has a good linear relationship with Rct,and the detection limit of this method is 1.35 pmol/L.Both methods have good concentration sensitivity to MET in different concentration ranges,providing a powerful tool for the detection of MET.

Square wave voltammetric quantification of folic acid,uric acid and ascorbic acid in biological matrix

Nowadays, modified electrodes with metal nanoparticles have appeared as an alternative for the electroanalysis of various compounds. In this study, gold nanoparticles（GNPs） were chosen as interesting metal nanoparticles for modifying carbon paste electrode（CPE）. GNPs and the gold nanoparticles-modified carbon paste electrode（GNPs/CPE） were characterized by UV–Vis spectroscopy, transmission electron microscopy（TEM） and scanning electron microscopy（SEM）. GNPs/CPE as a simple and sensitive electrode was used to study three important biological molecules： folic acid（FA）, uric acid（UA） and ascorbic acid（AA）. Square wave voltammetry（SWV） was used as an accurate technique for quantitative measurements. A good linear relation was observed between anodic peak current（ipa） and FA（5.2 × 10（-6）– 2.5 × 10（-5）M）, UA（1.2 × 10（-6）– 2.1 × 10（-5）M） and AA（1.2 × 10（-6）– 2.5 × 10（-5）M） concentrations in simultaneous determination of these molecules.