POTENTIOMETRIC ENZYME ELECTRODES BASED ON SUBSTRATE RECYCLING AND MEDIATORLESS BIOELECTROCATALYSIS

A sensitive potentiometric enzyme electrode for lactate determination has been developed based on the bienzyme system lactate oxidase-peroxidase co-immobilized on the surface of carbonic material. Enzymatic oxidation of lactate results in the formation of hydrogen peroxide. The latter leads to a shift in the electrode potential due to mediatorless peroxidase catalysis of hydrogen peroxide electroreduction. The rate of potential increase is proportional to the concentration of lactate and the calibration curve is linear between 0.01 and 0.25 mM. For increasing the sensitivity, a recycling system containing additionally co-immobilized lactate dehydrogenase has been realized. In the presence of NADH, lactate dehydrogenase catalyses the reduction of pyruvate formed by lactate oxidation. In this way lactate oxidase and lactate dehydrogenase co-immobilized on the electrode surface form an enzyme recycling system, which has a higher sensitivity towards lactate. The detection limit of lactate is 100 nM.