Development and application of a biosensor for hypoxanthine in fish extract

A hypoxanthine biosensor was constructed using immobilized xanthine oxidase and a polarographic electrode. The enzyme was covalently immobilized on a commercially available preactivated nylon membrane. The polarographic electrode detected hydrogen peroxide and uric acid released during the enzymatic reaction. The electrode responded linearly to hypoxanthine concentration in the range 3.6–107 μM. When applied to the determination of hypoxanthine in several fish meats, the results obtained agreed well with those obtained by the conventional enzymatic method. More than 40 assays could be performed with the same membrane and each sample could be assayed in ca. 2–3 min. The biosensor provides a reliable, simple, rapid and economical method for the measurement of hypoxanthine, a useful indicator of fish freshness.