An amperometric xanthine biosensor was prepared by immobilizing xanthine oxidase (XOx) on the surface of a platinum (Pt) disk electrode. The Pt electrode was first covered with a polyelectrolyte multilayer (PEM) film composed of poly(allylamine hydrochloride) (PAH) and poly(vinyl sulfate) (PVS) to block the Pt surface from the access of uric acid, a reaction product of the XOx-catalyzed oxidation reaction of xanthine, because uric acid can be electrochemically oxidized on the Pt electrode to induce interference. The PEM film-covered Pt electrode was further modified with a XOx-containing multilayer film composed of XOx and poly(dimethyldiallylammonium chloride) (PDDA). The xanthine biosensors thus prepared can be used successfully for detecting xanthine in the concentration range of 3-300 μM. The output current of the sensors depended on the number of the XOx/PDDA layers in the film. The PAH/PVS layer was effective to eliminate the uric acid interference.
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