Reagentless hydrogen peroxide and glucose sensors based on peroxidase immobilized on graphite electrodes

The electrocatalytic reduction of hydrogen peroxide (H2O2) by horseradish peroxidase (HRP) immobilized on graphite electrodes without the addition of an electron mediator was found to start at + 600 mV vs. Ag/AgCl and the highest current was obtained at about −100 mV. With an applied potential of −50 mV and in the absence of soluble mediator, linear calibration curves for H2O2 were obtained between 0.5 μM and 250 μM and for β‐D‐glucose in air‐saturated solution between 2 μM and 0.5 μM (HRP co‐immobilized with glucose oxidase). Cross‐linking the enzymes with glutaraldehyde and bovine serum albumin was found to increase the stability of the sensors without causing mass transfer resistance within the enzyme layer. The response time was 5 seconds both for H2O2 and for glucose and the sample through put was 150 samples h−1. The glucose measurements were made in 0.1 M phosphate buffer, pH 6, where no interfering from physiological levels of ascorbic acid, uric acid, or paracetamol (acetaminophen) could be detected.