Abstract: A sensitive hypoxanthine biosensor was constructed using xanthine oxidase and a plate platinum electrode. The enzyme was conveniently immobilized on a silk protein membrane by glutaraldehyde. The electrode detected the hydrogen peroxide released during the enzymatic reaction. The electrode used very small quantity of enzyme and its detection limit of hypoxanthine was 1×10^-7 mol/L When applied to the determination of the freshness of fish, the results obtained agreed well with those obtained by the traditional methods——the method of total volatile basic nitrogen and the method of total colonies of microbe.

Key words: biosensor, hypoxanthine, total colonies of microbe, freshness of fish, xanthine, total volatile baaic nitrogen