ELECTRICAL COMMUNICATION BETWEEN ELECTRODES AND NAD(P)(+)-DEPENDENT ENZYMES USING PYRROLOQUINOLINEQUINONE-ENZYME ELECTRODES IN A SELF-ASSEMBLED MONOLAYER CONFIGURATION - DESIGN OF A NEW GLASS OF AMPEROMETRIC BIOSENSORS

The development of an amperometric sensor utilizing the NAD(P)(+)-cofactor-dependent enzyme, malic enzyme, is described using a quinone-enzyme monolayer-modified electrode. Pyrroloquinolinequinone (PQQ, 1) was covalently linked to a self-assembled monolayer of cysteamine on an Au electrode. The resulting PQQ-monolayer electrode (PQQ surface coverage 1.98 x 10(-10) mol.cm(-2)) catalyzes the electrooxidation of NADPH and NADH. The developed anodic currents are controlled by NAD(P)H concentrations and provide an amperometric sensor for the cofactor. Melic enzyme has been covalently linked to the PQQ-monolayer electrode. The resulting PQQ-enzyme electrode (enzyme coverage 4.01 x 10(-12) mol.cm(-2)) provides an amperometric biosensor for the determination of melic acid in the presence of the cofactor NADP(+). In this system, biocatalyzed oxidation of malic acid generates NADPH that is oxidized by the PQQ component.