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  • 1
    ISSN: 0006-3592
    Keywords: D-lactate ; biosensor ; on-line monitoring ; fermentation ; carbon paste electrode ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The production of D-lactic acid by Lactobacillus delbrueckii (ATCC 9649) during fermentation was monitored on-line with a reagentless D-lactate dehydrogenase modified carbon paste electrode in a flow injection system integrated with a filtration sampling device. The time delay between sampling and detection was approximately 6 min. The use of an electropolymerized ortho-phenylenediamine membrane on the elctrode resulted in a very selective sensor response with acceptable stability and sensitivity. The D-lactate concentrations determined on-line agreed well with those determined by a standard method, suggesting that this sensor system is suitable for on-line monitoring of fermentation processes. © 1995 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1040-0397
    Keywords: Biosensor ; Aldose ; Ferrocene ; Carbon paste electrode ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The aim of this work was to improve an aldose-detecting biosensor based on quinoprotein aldose dehydrogenase (ALDH). Polymer-bound ferrocene derivatives with four different structures were studied as electron transfer mediators between the coenzyme of ALDH, pyrroloquinoline qninone (PQQ), and the conducting electrode material. The ferrocene polymers were mixed into carbon paste, which was used for the preparation of aldose-detecting electrodes by immobilizing ALDH on the carbon paste surface by adsorption. The current responses of the ferrocene polymer modified electrodes were studied and the effect of the polymer structure on the response was examined. The electrodes modified with all four polymers showed maximum response at the working potential around 300 mV (vs. Ag/AgCl). The operational stability of the ferrocene polymer modified electrodes was better than that of corresponding dimethylferrocene modified electrodes. The ferrocene polymer modified electrodes seemed to be suitable for the measurement of real samples.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1040-0397
    Keywords: NADH ; Ethylenimine ; Redox polymers ; Biosensors ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electrocatalytic oxidation of nicotinamide adenine dinucleotide (NADH) by two redox polymers was evaluated from steady-state measurements at drop-coated solid graphite electrodes in 0.25 M phosphate buffer, pH 7.0, at 0 mV (vs. SCE). The redox polymers studied comprised a styrene polymer incorporating positive charges through quaternary amines and Toluidine Blue 0 (TBO) moieties (ST) and a branched polyethylenimine with part of its primary amine groups loaded with TBO (PE). The catalytic efficiencyjudged from the maximum NADH sensitivity for the PE polymer was estimated to be 230 μa cm.-2 mM-1 at a coverage of 40 μgcm-2 and for the ST polymer 300 μAcm-2 cmM-1 at about 100 μg cm-2. Reagentless biosensors sensing D-glucose and L-malate were constructed from bulk modified carbon paste containing the PE redox polymer, NAD+, polyethylenimine (PEI) and D-glucose dehydrogenase or L-malate dehydrogenase. The D-glucose and L-malate sensors were characterized in a flow injection system by apparent j′max- and K′M-values of 230 μA cm-2 and 62mM and 3.3 μAcm-2 and 1.7mM, respectively. It was shown for glucose dehydrogenase that the presence of PEI in the paste in addition to the PE polymer, drastically improved the enzymatic conversion of glucose to gluconic acid.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1040-0397
    Keywords: Peroxidases ; Hydrogen peroxide ; Carbon paste electrodes ; Amperometric ; Organic-phase biosensor ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Biosensor characteristics of peroxidase-lactitol-modified carbon paste microclectrodes have been evaluated in aqueous and partial aqueous media (H2O-10% v./v. CH3OH and H2O-10% v./v. CH3CN), for hydrogen peroxide and 2-butanone peroxide amperometric detection, using a flow injection system. The activity of the investigated peroxidases (horseradish and fungal peroxidase from Arthromyces ramosus) was higher for hydrogen peroxide than for 2-butanone peroxide, irrespective of the solvent composition. For both peroxidases, the microelectrodes' sensitivity, estimated from the slopes of the linear domains as well as calculated from the Eddie-Hofstee plots decreased in the sequence: H2O 〉 H2O-10% v./v. CH3CN 〉 H2O-10% v./v. CH3OH. It is suggested that this behavior was due to the difference between the polarity and other physical properties, such as kinematic viscosity and dielectric constant of the nonaqueous solvents.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1040-0397
    Keywords: Carbon paste ; Impedance spectroscopy ; Cyclic voltammetry ; Electrochemical pretreatment ; Bovine serum albumin ; Polyethyleneimine ; Kanamycin ; Chitosan glutamate ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electrochemical properties of carbon paste electrodes (CPEs), including unmodified and modified with protein and polycations, were investigated by impedance spectroscopy (IS) using ferricyanide and ferrocene monocarboxylic acid (FcMA) as redox probes. Various electrochemical pretreatments were applied to the unmodified CPE. The heterogeneous charge transfer rate constant of ferro/ferricyanide couple is enhanced by 2 to 10 times compared with that obtained at untreated electrodes. It was found that for ferricyanide the more suitable pretreatments are successive cyclic voltammetric scans, cathodization and a square wave-like stepping rather than high-potential anodization. However, the pretreatment only exhibits a slight effect on the kinetics of FcMA. At the CPEs containing modifier, the electron transfer rate of the redox couple depends more on the pH of electrolyte solution if ferro/ferricyanide is used. The results can be explained by the differently charged states of the CPEs that were caused by the protonation or deprotonation of the modifiers in various pH solutions and demonstrate the importance of the electrostatic interaction on the kinetics of the highly polar species such as ferricyanide. The different adsorptive behavior of ferricyanide and FcMA is also discussed.
    Additional Material: 8 Ill.
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  • 6
    ISSN: 1040-0397
    Keywords: Amperometry ; Composite electrode ; Tyrosinase ; Catechol ; Teflon ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Amperometric biosensors incorporating tyrosinase into Teflon/graphite composite were developed for the detection of catechol. The homogeneity of Teflon/graphite was elucidated by means of chronoamperometry (using ferricyanide) and the calculation of the electrochemically active and total surface area of the electrodes. The homogeneity of composite is increased when working with the frozen Teflon. The mechanical strength, sensitivity, apparent Michaelis-Menten constant, maximum currents, and the compatibility with methanol and acetonitrile of the bioelectrodes were investigated. It was found that 10-30% of graphite in Teflon were suitable for the preparation of electrodes of high mechanical strength and low electrical resistivity. The sensitivity was found to be dependent on the ratio of Teflon/graphite where higher percentage of graphite gave the highest sensitivity. Electrode responses for catechol decreased 5% during one hour of its operation in buffer solution containing 10% methanol.
    Additional Material: 3 Ill.
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  • 7
    ISSN: 1040-0397
    Keywords: Tyrosinase ; Zeolite ; Biosensor ; Phenols ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The dependence of electrode response on additive properties in enzyme-modified carbon paste was studied. Four different HY-zeolite powders, dealuminated to different extents and characterized by both Si/Al ratio and hydrophilicity, were used as the carbon paste modifiers. The enzyme tyrosinase used in biosensors for the detection of catechol and other phenolic compounds was chosen as the model system for the construction of a composite carbon paste biosensor incorporating different HY-zeolites as additives. Tyrosinase was trapped on the HY-zeolite particles from a buffer solution, dried and mixed with graphite powder and a pasting oil. It was found that by incorporating HY-zeolites into the carbon paste the heterogeneous reaction rate of catechol redox conversion and the signal response for catechol were increased. In the latter case a higher response was observed for increased hydrophilicity, i.e., decreased Si/Al ratio of the HY-zeolite. The carbon paste/solution interface is considered to be an aqueous/organic phase and the characteristics of the enzyme- modified carbon paste electrode are related to theories, explaining enzymatic catalysis in organic solvents.
    Additional Material: 6 Ill.
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  • 8
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
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  • 9
    ISSN: 1436-5073
    Keywords: glucose determination ; enzyme electrode ; modified electrode ; flow injection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Glucose oxidase, mutarotase and bovine serum albumin were chemically crosslinked with glutaraldehyde directly on the surface of a carbon rod, covered with a layer of sputtered palladium/gold to produce a catalytic electrode for hydrogen peroxide oxidation. The polymerization resulted in glucose sensors with response factors that were stable for months under different storage conditions. The thin membranes had a fast response so that flow injection peaks with a width at half peak height of 3 s could be recorded accurately. The detection limit was 0.5μM D-glucose and the response was linear up to 3 mM D-glucose.
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  • 10
    ISSN: 1436-5073
    Keywords: glucose ; microdialysis ; ‘wired’ glucose oxidase ; amperometric detection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In-vitro on-line glucose monitoring is described, based on microdialysis sampling and amperometric detection operated in a flow-injection system. Samples were injected into a two-electrode microcell containing an Ag/AgCl quasi-reference electrode and a glucose enzyme electrode as the working electrode, operated at + 0.15 Vvs. Ag/AgCl. The enzyme electrode is constructed by mixing the ‘wired’ glucose oxidase into carbon paste. {Poly[1-vinylimidazole osmium(4,4′-dimethylbipyridine)2Cl)]}+/2+ was used to ‘wire’ the enzyme. The non-coated electrodes, cross-linked with poly(ethylene glycol) diglycidyl ether, responded linearly to glucose concentrations up to 60 mM, and were characterized by a sensitivity of 0.23 μA mM−1 cm−2, when operated in flow injection mode and of 5.4 μAmM –1 cm–2 in steady-state conditions. This sensitivity of the resulting enzyme electrode was 50% lower than that of similarly prepared but non-cross-linked electrodes. However, the cross-linked electrodes showed superior operational and storage stabilities, which were further improved by coating the electrodes with a negatively charged Eastman AQ film. An in-house designed microdialysis probe, equipped with a polysulphone cylindrical dialysis membrane, yielded a relative recovery of 50–60% at a perfusion rate of 2.5 μl/min–1 in a well stirred glucose solution. The on-line set up effectively rejected common interferences such as ascorbic acid and 4-acetaminophen when present at their physiological concentrations.
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