Sol-gel derived carbon ceramic electrode bulk-modified with tris(1,10-phenanthroline-5,6-dione)iron(II) hexafluorophosphate and its use as an amperometric iodate sensor

A surface-renewable tris (1,10-phenanthroline-5, 6-dione) iron (II) hexafluorophosphate (FePD) modified carbon ceramic electrode was constructed by dispersing FePD and graphite powder in methyltrimethoxysilane (MTMOS) based gels. The FePD-modified electrode presented pH dependent voltammetric behavior, and its peak currents were diffusion-controlled in 0.1 mol/L Na2SO4 + H2SO4 solution (pH = 0. 4). In the, presence of iodate, clear electrocatalytic reduction waves were observed and thus the chemically modified electrode was used as an amperometric sensor for iodate in common salt. The linear range, sensitivity, detection limit and response time of the iodate sensor were 5 x 10(-6)-1 x 10(-2) mol/L, 7.448 muA.L/mmol, 1.2 x 10(-6) mol/L and 5 s, respectively. A distinct advantage of this sensor is its good reproducibility of surface-renewal by simple mechanical polishing.

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.

Sol-gel-derived amperometric biosensor for hydrogen peroxide based on methylene green incorporated in Nafion film

A hydrogen peroxide biosensor was fabricated by coating a sol-gel-peroxidase layer onto a Nafion-methylene green modified electrode. Immobilization of methylene green (MG) was attributed to the electrostatic force between MG(+) and the negatively charged sulfonic acid groups in Nafion polymer, whereas immobilization of horseradish peroxidase was attributed to the encapsulation function of the silica sol-gel network. Cyclic voltammetry and chronoamperometry were employed to demonstrate the feasibility of electron transfer between sol-gel-immobilized peroxidase and a glassy carbon electrode. Performance of the sensor was evaluated with respect to response time, sensitivity as well as operational stability. The enzyme electrode has a sensitivity of 13.5 mu A mM(-1) with a detection limit of 1.0 x 10(-7) M H2O2, and the sensor achieved 95% of the steady-state current within 20 s. (C) 2000 Elsevier Science B.V. All rights reserved.

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.

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.

Acid-stable amperometric soybean peroxidase biosensor based on a self-gelatinizable grafting copolymer of polyvinyl alcohol and 4-vinylpyridine

A peroxidase was extracted from Chinese soybean seed coat, and its thermostability and acid-stability were characterized. This peroxidase was immobilized into a self-gelatinizable grafting copolymer of polyvinyl alcohol with 4-vinylpyridine(PVA-g-PVP) to construct an acid-stable hydrogen peroxide biosensor. The effect of pH was studied for optimum analytical performances by amperometric and spectro-photometric methods, also the K-m(app) and the stability of the soybean peroxidase-based biosensor are discussed. At pH 3.0, the soybean peroxidase maintained its bioactivity and the enzyme electrode had a linear range from 0.01 to 6.2 mM with a detection limit of 1.0 x 10(-7) M. In addition, the main characteristics of different hydrogen peroxide sensors were compared.

Self-gelatinizable graft copolymer of poly(vinyl alcohol) with 4-vinylpyridine as an immobilization matrix for the construction of a tyrosinase-based amperometric biosensor

A tyrosinase-based amperometric biosensor using a self-gelatinizable graft copolymer of poly(vinyl alcohol) with 4-vinylpyridine (PVA-g-PVP) as an immobilization matrix was constructed. The 4-vinylpyridine component of PVA-g-PVP enhances the adherence to a glassy carbon electrode surface. The content of 4-vinylpyridine in this immobilization matrix plays a key role in retaining the activity of tyrosinase. A simple, milder method was adopted by simply syringing the copolymer-tyrosinase aqueous solution on to the electrode surface and allowing water to evaporate at 4 degrees C in a refrigerator. Several parameters, including copolymer composition; pH, applied potential and enzyme membrane composition, ware optimized. The enzyme membrane composition can be varied to obtain higher sensitivity or a wider linear detection range. The biosensor was used for the determination of phenol, p-cresol and catechol. The biosensor exhibited excellent reproducibility, stability and sensitive response and can be used in flow injection analysis. The biosensor showed an extended linear range in hydrophilic organic solvents and it can be used in monitoring organic reaction processes. The analytical performance demonstrated this immobilization matrix is suitable for the immobilization of tyrosinase.

Functionalized inorganic-organic composite material derivated by sol-gel for construction of mediated amperometric hydrogen peroxide biosensor

A novel functionalized inorganic-organic hybrid material with cation exchange property was prepared by sol-gel method. The H2O2 biosensor was fabricated by simply dipping the horseradish peroxidase-containing functionalized membrane modified electrode into Meldola's blue (MDB) solution. MDB was adsorbed and firmly immobilized within the membrane. The electrochemical behavior of MDB incorporated in the membrane was more reversible compared with that of the solution species and suitable as mediator for the horseradish peroxidase. The response time was less than 25 s. Linear range is up to 0.6 mM (COH. coeff. 0.9998) with detection Limit of 9 x 10(-7) M. High sensitivity of 75 nA mu M cm(-2) was obtained due to high MDB-loading. The biosensor exhibited a good stability. (C) 1999 Elsevier Science B.V. All rights reserved.

AMPEROMETRIC BIOSENSORS BASED ON THE IMMOBILIZATION OF OXIDASES IN A PRUSSIAN BLUE FILM BY ELECTROCHEMICAL CODEPOSITION

Prussian blue has been formed by cyclic voltammetry onto the basal pyrolytic graphite surface to prepare a chemically modified electrode which provides excellent electrocatalysis for both oxidation and reduction of hydrogen peroxide. It is found for the first time that glucose oxidase or D-amino oxidase can be incorporated into a Prussian blue film during its electrochemical growth process. Two amperometric biosensors were fabricated by electrochemical codeposition, and the resulting sensors were protected by coverage with a thin film of Nafion. The influence of various experimental conditions was examined for optimum analytical performance. The glucose sensor responds rapidly to substrates with a detection limit of 2 x 10(-6) M and a linear concentration range of 0.01-3 mM. There was no interference from 2 mM ascorbic acid or uric acid. Another (D-amino acid) sensor gave a detection limit of 3 x 10(-5) M D-alanine, injected with a linear concentration range of 7.0 x 10(-5)-1.4 x 10(-2) M. Glucose and D-amino acid sensors remain relatively stable for 20 and 15 days, respectively. There is no obvious interference from anion electroactive species due to a low operating potential and excellent permselectivity of Nafion.

SURFACE MODIFICATION OF ELECTRODES FOR AMPEROMETRIC BIOSENSORS IN ANALYTICAL-CHEMISTRY

Amperometric biosensors based on surface modifications of electrodes are described. Cobalt porphyrins modified on glassy carbon and carbon fiber electrodes can greatly decrease the overpotential and increase the sensitivity of detection due to EC electroc

ELECTROCATALYTIC OXIDATION AND AMPEROMETRIC DETERMINATION OF SULFHYDRYL COMPOUNDS AT A COPPER HEXACYANOFERRATE FILM GLASSY-CARBON ELECTRODE IN LIQUID-CHROMATOGRAPHY

Electrocatalytic oxidation of sulfhydryl compounds was effective on a copper hexacyanoferrate (CuHCF) film glassy carbon electrode, at a significantly reduced overpotential (0.55 to 0.65 V) and for a broader pH range (2.0 to 7.0). The electrocatalysis was

FLOW-INJECTION ANALYSIS OF GLUCOSE AT AN AMPEROMETRIC GLUCOSE SENSOR-BASED ON ELECTROCHEMICAL CODEPOSITION OF PALLADIUM AND GLUCOSE-OXIDASE ON A GLASSY-CARBON ELECTRODE

A glassy carbon electrode (GCE) modified with palladium provides excellent electrocatalytic oxidation of hydrogen peroxide. When the electrolyte contains palladium chloride and glucose oxidase, the GCE can be modified by electrochemical codeposition at a given potential. The resulting modified surface was coated with a thin film of Nation to form a glucose sensor. Such a glucose sensor was successfully used in the flow-injection analysis of glucose with high stability and anti-poisoning ability. It gave a detection limit of 1 X 10(-7) M injected glucose, with a linear concentration range of 0.001-8 mM. There is no obvious interference from substances such as ascorbate and saccharides.

Microprojectile bombardment of Laminaria japonica gametophytes and rapid propagation of transgenic lines within a bubble-column bioreactor

A human acidic fibroblast growth factor gene, hafgf, was successfully transferred into Laminaria japonica (kelp) gametophytes via microprojectile bombardment using the biolistic PDS-1000/He gene gun. Following phosphinothricin screening, PCR detection and Southern blot analysis, transgenic L. japonica gametophytes were cultivated in an illuminated bubble-column bioreactor to optimize growth conditions. A maximal final dry cell density of 1,695 mg l(-1) was obtained in a batch culture having an initial dry cell density of 129.75 mg l(-1). This was achieved using an aeration rate of 1.08 l air min(-1) l(-1) culture in a medium containing 1.5 mM inorganic nitrate and 0.15 mM phosphate. In addition, the relationship between different nitrogen sources and growth of transgenic gametophytes indicated that both urea and sodium nitrate were effective nitrogen sources for cell growth, while ammonium ions inhibited growth of these gametophytes.

Analysis of carbohydrates in a tibetan medicine using new labeling reagent, 1-(2-naphthyl)-3-methyl-5-pyrazolone, by HPLC with DAD detection and ESI-MS identification

A new labeling reagent, 1-(2-naphthyl)-3-methyl-5-pyrazolone (NMP), coupling with liquid chromatography (LC) with electrospray ionization mass spectrometry (ESI-MS) for the detection of carbohydrates from a famous Tibetan medicine is reported. Carbohydrates were derivatized to their bis-NMP-labeled derivatives. The method, in conjunction with a gradient elution, offered a baseline resolution of carbohydrate derivatives on a reversed phase Hypersil ODS-2 column. The carbohydrates such as mannose, galacturonic acid, glucuronic acid, rhamnose, glucose, galactose, xylose, arabinose, and fucose could be successfully detected by UV and ESI-MS. Derivatives showed intense protonated molecular ion at m/z [M+H]+ in positive ion mode. The mass to charge ratios of characteristic fragment ions at m/z 473.0 could be used for the accurately qualitative identification of carbohydrates; this characteristic fragment ion was from the cleavage of C2-C3 bond in the carbohydrate chain giving the specific fragment ions at m/z [MH-CmH2m+1Om-H2O](+) for pentose, hexose, and glyceraldehydes, and at m/z [MH-CmH2m-1Om+1-H2O](+) for alduronic acids, such as galacturonic acid and glucuronic acid (m=n-2, n is carbon atom number of carbohydrate). Compared with the traditional 1-phenyl-3-methyl-5-pyrazolone (PMP) reagent, currently synthesized NMP show the advantage of higher sensitivity to carbohydrate compounds with UV and ESI-MS detection.