Amperometric Enzyme Electrodes for Substrates of Immobilized Pyranose Oxidase

Two kinds of biosensors for the determination of pyranose oxidase substrates were developed, based on the detection of evolving hydrogen peroxide on a platinum or platinized graphite electrode at +650 or +400 mV, respectively. The membranes consisted of enzyme immobilized by covalent bonds on nylon net and were stable for 8 months of dry storage at 4 °C. In addition to D-glucose, low concentrations of D-xylose, D-galactose and L-sorbose can also be measured with the biosensor. The shift of the optimum pH of the immobilized enzyme to the alkaline region (8.0 - 9.5) is convenient for the borate buffer medium which extends the linear concentration region of the biosensor to 15 mmol l-1 for D-galactose, 30 mmol l-1 for D-xylose and 30 mmol l-1 for maltose. L-Sorbose provides no response up to a concentration of 10 mmol l-1 in 0.05 M borate and up to a concentration of 30 mmol l-1 in 0.2 M borate at pH 9.2. Interfering D-glucose was eliminated up to 2.5 mmol l-1 by means of an enzyme pre-membrane with immobilized hexokinase. The effect of ascorbate was eliminated, up to 75 mmol l-1, by using a cellulose acetate electrostatic barrier. D-Galactose, however, decreases the sensor response to D-glucose.