Xiangqin Lin

Electrochemical preparation, characterization and application of electrodes modified with hybrid hexacyanoferrates of copper and cobalt

Abstract Hybrid copper–cobalt hexacyanoferrate (CuCoHCF) films were electrodeposited on a platinum electrode or a glassy carbon electrode by cyclic voltammetry and characterized by electrochemistry, XRD, ICP–AES and XPS. The results indicated that CuCoHCF was a substitution-type hybrid hexacyanoferrate. With the increase of Cu2+ content in the deposition solution, the Cu2+ content in the films increased correspondingly, while the lattice constant of the films decreased gradually. The CuCoHCF modified platinum electrode exhibited stable electrochemical responses in a wide pH range of 4–10 and permeability for monovalent cations in the order of K+>Li+>Na+>NH4+, both of which are different from those of the respective single component copper or cobalt hexacyanoferrates. XPS gave direct evidence that the iron element existed in the form of Fe(III) in oxidized films and was reduced to Fe(II) during X-ray scanning. K+ was incorporated into and excluded from CuCoHCF films to maintain electrical neutrality during the reduction and oxidation process, respectively. The CuCoHCF modified glassy carbon electrode exhibited obvious electrocatalytic activity towards both reduction and oxidation of hydrogen peroxide. When a cathodic catalytic current was used, the sensor exhibited a linear response in a hydrogen peroxide concentration range of 2.3×10−3–8.1×10−7 M with a detection limit of 6.6×10−8 M. The hydrogen peroxide sensor showed excellent stability and anti-interference ability towards oxygen and other easily oxidized compounds due to a low applied potential of 0.02 V, which is a great merit for further application in the field of biosensors.

Covalent modification of glassy carbon electrode with glutamic acid for simultaneous determination of uric acid and ascorbic acid

A novel covalently modified glassy carbon electrode with glutamic acid has been fabricated via an electrochemical oxidation procedure and was applied to the catalytic oxidation of uric acid (UA) and ascorbic acid (AA), reducing the overpotentials by about 0.2 V and 0.3 V, respectively. Based on its strong catalytic function toward the oxidation of UA and AA, the modified electrode resolved the overlapping voltammetric response of UA and AA into two well-defined voltammetric peaks with both cyclic voltammetry (CV) and differential pulse voltammetry (DPV), which can be used for the simultaneous determination of these species in a mixture. The catalytic peak current obtained from DPV was linearly dependent on the UA and AA concentration in the range 2 x 10(-6)-4 x 10(-4) mol L-1 and 1.0 x 10(-6)-4 x 10(-4) mol L-1 with correlation coefficients of 0.996 and 0.997, respectively. The detection limits (3 delta) for UA and AA were 1.1 x 10(-6) mol L-1 and 9.2 x 10(-7) mol L-1, respectively. The modified electrode shows good sensitivity, selectivity and stability, and has been applied to the determination of UA and AA simultaneously in human urine samples with satisfactory results.

Immobilization of DNA on carbon fiber microelectrodes by using overoxidized polypyrrole template for selective detection of dopamine and epinephrine in the presence of high concentrations of ascorbic acid and uric acid

The overoxidized polypyrrole (PPyox) film as a template for DNA immobilization has been demonstrated in this paper. The DNA molecules inserted into the micropores of the ultrathin PPyox matrix under the driving forces of an electric field and were firmly immobilized on the carbon fiber electrode (CFE). Such a DNA-PPyox biocomposite layer exhibited more effective rejection of anionic ascorbate (AA) and uric acid (UA) and more preferential collection of the cationic dopamine (DA) and epinephrine (EP) than pure PPyox and DNA coatings. The DPV peak currents increased linearly with increasing DA and EP concentrations in the range of 3.0 x 10(-7) to 1.0 x 10(-5) M and 5.0 x 10(-7) to 2.0 x 10(-5) M with the lowest detected concentrations of 8.0 x 10(-8) M and 6.0 x 10(-8) M, respectively. The electrochemical signal of AA could be totally suppressed under a concentration of 20 mM and beyond this concentration, the overlapped responses of AA, DA/EP and UA could be resolved into three well-defined voltammetric peaks. The selectivity factors k(DA/AA) and k(EP/AA) were about 5000 and 2000 for an equal concentration in the presence of 0.5 mM UA. The properties of the biocomposite film have been characterized by atomic force microscopy and electrochemical investigations.

Separation of anodic peaks of ascorbic acid and dopamine at an α-alanine covalently modified glassy carbon electrode

A covalently modified glassy carbon electrode with an α-alanine monolayer was fabricated and was applied to the electrocatalytic oxidation of ascorbic acid, reducing the overpotential by about 280 mV with an obviously increased current response. The catalytic current obtained from square-wave voltammetry was linearly dependent on ascorbic acid concentration in the range 2.0 × 10−5–5.0 × 10−3 mol L−1 with a correlation coefficient of 0.997. Owing to the catalytic effect of the modified film towards ascorbic acid, the modified electrode resolved the overlapped voltammetric responses of ascorbic acid and dopamine into two well-defined square wave voltammetric peaks with peak-to-peak separation in potentials of about 180 mV. This can be used to allow the determination of ascorbic acid in the presence of dopamine. The modified electrode showed good selectivity, stability and anti-fouling properties.

Selective Determination of Uric Acid by Using a β-Cyclodextrin Modified Electrode

A β-cyclodextrin (CD) modified poly(N-acetylaniline) (PNAANI) glassy carbon electrode (GCE) was used to study the electrode reaction of uric acid (UA). The formation of a supramolecular complex between β-CD and UA improves the sensitivity and selectivity of the UA determination. The mechanism of selective detection of UA at the β-CD/PNAANI/GCE is proposed. Also, an analytical procedure involving square-wave voltammetry has been developed for determination of UA in the concentration range 1.0×10−5 to 2.0×10−4 mol dm−3.

Amperometric Biosensor for Hydrogen Peroxide Based on Immobilization of Horseradish Peroxidase on Methylene Blue Modified Graphite Electrode

A methylene blue modified graphite electrode was first prepared by adsorbing the molecules on a spectrographic graphite disk electrode saturated with wax. Then, a novel hydrogen peroxide biosensor was fabricated based on immobilization of horseradish peroxidase on the methylene blue modified graphite electrode by cross-linking with glutaraldehyde. This electrode exhibited excellent electrochemical activity in aqueous solutions, and the electron transfer rate constant for the adsorbed methylene blue was determined as 0.12 s–1. It was demonstrated that the modified methylene blue molecules could shuttle electrons between immobilized HRP and graphite substrate very well for H2O2 sensing. The characteristics of this sensor were evaluated with respect to applied potential, pH and temperature. A detection limit of 3.0×10–6 mol/L hydrogen peroxide was examined at simple experimental conditions. Dopamine and ascorbic acid did not interfere with the determination. This sensor was also stable, reproducible and outstanding for long-term use.

Simultaneous determination of dopamine and ascorbic acid at glutamic acid modified graphite electrode

This paper reports the preparation of the glutamic acid chemically modified graphite electrode and its electrocatalytic function toward dopamine and ascorbic acid. The overlapped oxidation peaks of dopamine and ascorbic acid can be separated up to about 200 mV, which is large enough to determine both of them simultaneously in a mixture. The catalytic peak currents obtained from the cyclic voltammograms are linearly related to both dopamine and ascorbic acid concentrations in the ranges of 6.0 × 10−6–8.0 × 10−4mol/L with correlation coefficient of 0.9976 for dopamine and 4.0 × 10−5–0.1 mol/L with correlation coefficient of 0.9982 for ascorbic acid. The detection limits (3σ) for dopamine and ascorbic acid are 1.8 × 10−6mol/L and 1.3 × 10−5mol/L, respectively. The modified electrodes showed high catalyticability and good stability. The proposed method has been successfully applied to the simultaneous determination of dopamine and ascorbic acid in samples.

In situ external reflection FTIR spectroelectrochemical investigation of poly(o-phenylenediamine) film coated on a platinum electrode

The electrochemically deposited poly(o-phenylenediamine) film on a Pt electrode has been investigated utilizing in situ external reflection FTIR spectroelectrochemistry technique. The prepared ladder polymer film is found to be partially ring-opened. The dopant ClO4- is evidenced to orient in such a way that more than one oxygen atom attach to the charge sites of the polymer. This suggests that positive charges of oxidized polymer are partially delocalized over the whole chains. The proton movement observed during the oxidation reaction is associated with the solvated MeCN molecule. It is proposed that the proton diffusion, dissolvation and protonation of the film may be essential to the electrochemical reduction reaction of the film. Copyright (C) 1996 Elsevier Science Ltd.

Selective determination of dopamine in the presence of ascorbic acid at an over-oxidized poly(N-acetylaniline) electrode

An over-oxidized poly(N-acetylaniline) (PNAANI)/GCE was used to determine dopamine (DA) in a large excess of ascorbic acid (AA) by differential pulse voltammetry. A linear relation between Ip and DA concentration was found over the range 5.0 x 10(-7) to 2.0 x 10(-5) M. The detection limit was 1.68 x 10(-8) M for S/N = 3 and 400 microM AA did not interfere with the DA determination. The high sensitivity was due to accumulation and selectivity was due to charge discrimination. The mechanism of selective determination of DA at over-oxidized PNAANI/GCE was also proposed.

Multi-mode in situ spectroelectrochemical studies of redox pathways of adrenaline

Abstract The electrochemical oxidation–reduction processes of adrenaline were studied by multi-mode in situ spectroelectrochemistry involving thin-layer cyclic voltammetry, UV–vis absorption, fluorescence spectroelectrochemistry and electrogenerated chemiluminescence based on a versatile long path-length thin-layer electrochemical cell with a glassy carbon working electrode. It was found that the redox pathways were related to the pH of the solution, the potential window and the oxygen dissolved in the solution. A mechanism was proposed for the redox process under different conditions. Furthermore, the reaction pathway for the electrooxidation of adrenaline was compared with the pathway for the permanganate oxidation of adrenaline, and a possible reason for the fact that the electrooxidation of adrenaline cannot generate chemiluminescence was proposed.