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-peroxi dase co-immobilized on the surface of carbonic material. Enzymatic oxi dation of lactate results in the formation of hydrogen peroxide. The l atter leads to a shift in the electrode potential due to mediatorless peroxidase catalysis of hydrogen peroxide electroreduction. The rate o f potential increase is proportional to the concentration of lactate a nd the calibration curve is linear between 0.01 and 0.25 mM. For incre asing the sensitivity, a recycling system containing additionally co-i mmobilized lactate dehydrogenase has been realized. In the presence of NADH, lactate dehydrogenase catalyses the reduction of pyruvate forme d by lactate oxidation. In this way lactate oxidase and lactate dehydr ogenase co-immobilized on the electrode surface form an enzyme recycli ng system, which has a higher sensitivity towards lactate. The detecti on limit of lactate is 100 nM.