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)(+)-cofa ctor-dependent enzyme, malic enzyme, is described using a quinone-enzy me 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 coverag e 1.98 x 10(-10) mol.cm(-2)) catalyzes the electrooxidation of NADPH a nd NADH. The developed anodic currents are controlled by NAD(P)H conce ntrations and provide an amperometric sensor for the cofactor. Melic e nzyme has been covalently linked to the PQQ-monolayer electrode. The r esulting 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, biocatal yzed oxidation of malic acid generates NADPH that is oxidized by the P QQ component.