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In order to prepare a biosensor for the determination of uric acid, electropolymerization of pyrrole on Pt surface was carried out with an electrochemical cell containing pyrrole, ferrocene (as a electron mediator) and tetrabutylammonium tetrafluoroborat in acetonitrile by cyclic voltammetry between 0.0 and 1.0 V (vs. Ag/AgCl) at a scan rate of 50 mV/s upon Pt electrode. Uricase was immobilized by a glutaraldehyde/gelatine croslinking procedure on to polypyrrole film after the electropolymerization processes. The response of the biosensor against uric acid was measured after 330 seconds following the application of a constant potential of +0.7 V (vs. Ag/AgCl). The resulting biosensor exhibits excellent electrocatalysis for the uric acid. The amperometric determination is based on the electrochemical detection of H2O2, which is generated in enzymatic reaction of uric acid. The sensor responds to uric acid with a detection limit of 5.0 x 10(-7) M. The sensor remains relatively stable for 5 weeks. Interference effect were investigated on the amperometric response of the biosensor. Determination of uric acid was carried out in the biological fluids by biosensor.

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A new amperometric biosensor was developed for determining hypoxanthine in fish meat. Xanthine oxidase with pyrrole and polyvinylsulphonate was immobilized on the surface of a platinum electrode by electropolymerization. The determination of xanthine-hypoxanthine was performed by means of oxidation of uric acid liberated during the enzyme reaction on the surface of the enzyme electrode at + 0.30V (SCE). The effects of pH, substrate concentration, and temperature on the response of the xanthine-hypoxanthine biosensor were investigated. The linear working range of the enzyme electrode was 1.0 × 10(-7) -1.0 × 10(-3) M of the hypoxanthine concentration, and the detection limit was 1.0 × 10(-7)M. The apparent K(m(app)) and I(max) of the immobilized xanthine oxidase were found to be 0.0154 mM and 1.203 μA/mM, respectively. The best pH and temperature value for xanthine oxidase were selected as 7.75 and 25°C, respectively. The sensor was used for the determination of hypoxhantine in fish meat. Results show that the fish degraded very rapidly after seven days and the hypoxanthine amount was found to increase over days of storage.

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