Sol-gel-derived ceramic carbon composite electrode containing isopolymolybdic anions

A new class of polyoxomelalate (POM)-modified electrodes is fabricated by the sol-gel technique and demonstrated for nitrite sensing. The electrode material comprises an interconnected dispersion of graphite powder and a uniform dispersion of isopolymolybdic anions (Mo8O26) in a porous methylsilicate matrix. The chemically modified electrodes showed well-defined cyclic voltammograms with three reversible redox couples in acidic aqueous solutions because of the good physicochemical compatibility of Mo8O26 and the carbon ceramic matrix. The Mo8O26-modified electrodes show good stability and reproducibility, especially the renewal repeatability by simple polishing in the event of surface fouling. (C) 2000 Elsevier Science Ltd. All rights reserved.

Sol-gel-derived, polishable, 1 : 12-phosphomolybdic acid-modified ceramic-carbon electrode and its electrocatalytic oxidation of ascorbic acid

Novel ceramic-carbon electrodes (CCEs) containing 1:12-phosphomolybdic acid (PMo12) were constructed by homogeneously dispersing PMo12 and graphite powder into methyltrimethoxysilane-derived gel. Peak currents for the PMo12-doped CCE were surface-controlled at lower scan rates but diffusion-controlled at higher scan rates and peak potentials shifted to the negative potential direction with increasing pH. In addition, the electrode exhibited electrocatalytic activity toward the oxidation of ascorbic acid. The PMo12-modified CCE presented good chemical and mechanical stability and good surface renewability (ten successive polishing resulted in less than 5% relative standard deviation). (C) 2000 Elsevier Science B.V. All rights reserved.

Amperometric quantification of polar organic solvents based on a tyrosinase biosensor

A novel amperometric biosensor for quantification of the electrochemically inert polar organic solvents based on tyrosinase electrode was preliminarily reported. The biosensor was fabricated by simply syringing an aqueous solution of tyrosinase/PVAVP (PVAVP: copolymer of poly(vinyl alcohol) grafting with 4-vinylpyridine) onto glassy carbon electrode surface followed by drying the modified electrode at +4 degrees C in a refrigerator. The current generated from electrochemical reduction of quinone is a probe signal. The biosensor can be used for quantification of polar organic solvents, and its mechanism was characterized with in situ steady-state amperometry-quartz crystal microbalance experiments. The detection limit, sensitivity, and dynamic range for certain organic solvents are dependent on the kind and concentration of the substrate probe and the hydrophobicity of the immobilization matrix. The response time for all the tested organic solvents is less than 2 min.

Amperometric glucose biosensor based on lipid film

A novel glucose biosensor based on cast lipid film was developed. This model of biological membrane was used to supply a biological environment on the surface of the electrode, moreover it could greatly reduce the interference and effectively exclude hydrophilic electroactive material from reaching the detecting surface. TTF was selected as a mediator because of its high electron-transfer efficiency, and it was incorporated in the lipid film firmly. Glucose oxidase was immobilized in hydrogel covered on the lipid film. The effects of pH, operating potential were explored for the optimum analytical performance by using amperometric method. The response time of the biosensor was less than 20 s, and the linear range is up to 10 mmol l(-1) (corr. coeff. 0.9932) with the detection limit of 2 x 10(-5) mol l(-1). The biosensor also exihibited good stability and reproducibility. (C) 2000 Elsevier Science S.A. All rights reserved.

Mass spectrometry study on snake venoms and enzymes

In this paper, three kinds of snake venoms and lour kinds of enzymes (phospholipase A(2), fibrinolytic enzyme, arginine esterase and L-amino acid oxidase) isolated from the snake venom were analyzed. As the snake venom was different, the MALDI/TOF/MS showed difference, The MALDI/TOF/MS determination results could be affected Ly the concentrations of snake venom enzymes, And the mechanisms of desorption and ionization was also given in this study, By using MALDI/TOF/MS we obtained the accurate molecular weights and homogeneities of the enzymes. The apparent characteristics of the positive MALDI/TOF/MS of enzymes composed by two subunits were also given out, The results showed that MALDI/TOF/MS is an effective analytic method for discovering new components from snake venom complexes. And it is reliable to use this method to determine the molecular weights and purifies of protein molecules.

Amperometric enzyme electrode for the determination of hydrogen peroxide based on sol-gel/hydrogel composite film

A new type of organic-inorganic composite material was prepared by sol-gel method, and a peroxidase biosensor was fabricated by simply dropping sor-gel-peroxidase mixture onto glassy carbon electrode surface. The sol-gel composite film and enzyme membrane were characterized by Fourier-transform infrared (FT-IR) spectroscopy and EQCM, the electrochemical behavior of the biosensor was studied with potassium hexacyanoferrate(II) as a mediator, and the effects of pH and operating potential were explored for optimum analytical performance by using amperometric method. The response time of the biosensor was about 10 s; the linear range was up to 3.4 mM with a detection limit of 5 x 10(-7) M. The sensor also exhibited high sensitivity (15 mu A mM(-1)) and good long-term stability. In addition, the performance of the biosensor was investigated using flow injection analysis (FIA), and the determination of hydrogen peroxide in real samples was discussed. (C)2000 Elsevier Science B.V. All rights reserved.

Assembly of alternating polycation and DNA multilayer films by electrostatic layer-by-layer adsorption

The assembly of alternating DNA and positively charged poly(dimethyldiallylammonium chloride) (PDDA) multilayer films by electrostatic layer-by-layer adsorption has been studied. The real-time surface plasmon resonance (BIAcore) technique was used to characterize and monitor the formation of multilayer films in solution in real time continuously. Electrochemical impedance spectroscopy (EIS) and UV-vis absorbance measurements were also used to study the film assembly, and linear film growth was observed. All the results indicate that the uniform multilayer can be obtained on the poly(ethylenimine)- (PEI-) coated substrate surface. The kinetics of the adsorption of DNA on PDDA surface was also studied by the real-time BIAcore technique; the observed rate constant was calculated using a Langmuir model (k(obs) = (1.28 +/- 0.08) x 10(-2) s(-1).

Ceramic carbon/polypyrrole materials for the construction of bienzymatic amperometric biosensor for glucose

A novel amperometric glucose biosensor was constructed by electrochemical formation of a polypyrrole (PPy) membrane in the presence of glucose oxidase (GOD) on the surface of a horseradish peroxidase (HRP) modified ferrocenecarboxylic acid (FCA) mediated sol-gel derived ceramic carbon electrode. The amperometric detection of glucose was carried out at +0.16 V (vs. SCE) in 0.1 mol/L phosphate buffer solution (pH 6.9) with a linear response range between 8.0x10(-5) and 1.3x10(-3) mol/L of glucose. The biosensor showed a good suppression of interference and a negligible deviation in the amperometric detection.

Amperometric biosensor for hydrogen peroxide based on sol-gel/hydrogel composite thin film

A reagentless amperometric hydrogen peroxide biosensor was developed. Horseradish peroxidase (HRP) was immobilized in a novel sol-gel organic-inorganic hybrid matrix that is composed of silica sol and a grafting copolymer of poly(vinyl alcohol) with 4-vinylpyridine (PVA-g-PVP). Tetrathiafulvalene (TTF) was employed as a mediator and could lower the operating potential to -50 mV (versus Ag/AgCl). The sensor achieved 95% of the steady-state current in 15 s. Linear calibration for hydrogen peroxide was up to 1.3 mM with the detection limit of 2.5 x 10(-7)M. The enzyme electrode retained about 94% of its initial activity after 30 days of storage in a dry state at 4 degreesC.

Hydrogen peroxide biosensor with enzyme entrapped within electrodeposited polypyrrole based on mediated sol-gel derived composite carbon electrode

A novel amperometric biosensor for the detection of hydrogen peroxide was described. The biosensor was constructed by electrodepositing HRP/PPy membrane on the surface of ferrocenecarboxylic acid mediated sol-gel derived composite carbon electrode. The biosensor gave response to hydrogen peroxide in a few seconds with detection limit of 5.0 x 10(-5) M (based on signal:noise = 3). Linear range was upto 0.2 mM. The biosensor exhibited a good stability. (C) 2001 Elsevier Science B.V. All rights reserved.

A hydrogen peroxide biosensor combined HRP doped polypyrrole with ferrocene modified sol-gel derived composite carbon electrode

A novel amperometric biosensor for the detection of hydrogen peroxide is described. The biosensor was constructed by electrodepositing HRP/PPy membrane on the surface of ferrocenecarboxylic acid mediated sol-gel derived composite carbon electrode. The biosensor gives response to hydrogen peroxide in a few seconds with detection limit of 5x10(-7) mol (.) L-1 (based on signal : noise=3). Linear range is up to 0.2 mmol (.) L-1.

Hydrogen peroxide biosensor based on sol-gel-derived glasses doped with Eastman AQ polymer

A hydrogen peroxide biosensor based on sol-gel-derived glasses doped with poly(ester sulfonic acid) Eastman AQ 55D was constructed. Thionine (TH), as a mediator, was incorporated in this matrix by electrostatic force between TH+ and the negatively charged sulfonic acid group in Eastman AQ polymer. Performance and characteristics of the sensor were evaluated with respect to response time, sensitivity and storage stability. The enzyme electrode has a sensitivity of 11.36 muA mM(-1) with a detection limit of 5.0 x 10(-7) M H2O2, and the sensor achieved 95% of the steady state current within 20 s. (C) 2001 Elsevier Science B.V. All rights reserved.

Cobalt(II)hexacyanoferrate film modified glassy carbon electrode for construction of a glucose biosensor

An amperometric glucose biosensor was constructed based on a glassy carbon electrode modified with a Cobalt(II)hexacyanoferrate film which catalyzes electroreduction of hydrogen peroxide. Gelatin was used as immobilization matrix. Interference could be effectively eliminated by the combination of low detection potential with a Nafion coating. A low applied potential can avoid oxidation of interferences such as ascorbic acid, uric acid, p-acetyl-aminophenol, etc.. Nafion coating prevents interferences from access to the electrode surface by electrostatic repulsion. A wide linear range of detection was obtained. Analytical performance parameters are given and kinetic analysis discussed.

Sol-gel biosensor

yA review with 44 references is presented on the development of sol-gel-based biosensor. The main discussions are devoted to the process, advantages and properties of sol-gel immobilization method, sol-gel optical biosensor and amperometric biosensor, also the trend in this field is forecasted.

Chemiluminescent determination of glucose with a modified carbon paste electrode

A flow injection analysis detection method for glucose is presented which is based on the oxidation of glucose by glucose oxidase followed by chemiluminescent detection of hydrogen peroxide. Both glucose oxidase and hematin, a chemiluminescent reaction catalyst, were bulk-immobilized conveniently by direct mixing with carbon paste, which allows renewal of the electrode surface by simply polishing or cutting to expose a new and fully active surface in the case of fouling. Luminol in reagent solution passed through the flow cell and reacted with hydrogen peroxide produced by the enzyme reactor in the presence of the catalyst to yield light. An applied potential of -0.4 V avoided the electrode fouling effectively. The log-log plot of the emitted light intensity vs glucose concentration was linear over the range of 1-100 mmol L-1 with a correlation coefficient of 0.992. Application of this method to other chemiluminescent and bioluminescent systems is suggested. (C) 1999 Academic Press.