AMPEROMETRIC GLUCOSE SENSORS BASED ON IMMOBILIZED GLUCOSE-OXIDIZING ENZYMES AND CHEMICALLY MODIFIED ELECTRODES

Amperometric biosensors based on two different reaction mechanisms are presented. Common to both types is the combination of a selective enzymatic reaction with a selective mediated reaction that can be followed amperometrically at 0 mV vs. SCE and below. One type is based on the chemical modification of carbon pastes with a dehydrogenase, the necessary cofactor NAD+ and a redox mediator. In the presence of the enzyme substrate NADH will be produced. The high overvoltage for the electrochemical oxidation of the NADH is decreased by the addition of the redox mediator to the paste. The redox mediators used are phenoxazine derivatives, making the electrocatalytic oxidation of NADH possible at 0 mV vs. SCE and below. A glucose sensor based on glucose dehydrogenase is described. Another type is based on the co-immobilization of a hydrogen peroxide-producing oxidase with horseradish peroxidase onto the surface of solid graphite. The detection is based on an apparent direct electron transfer from the electrode to the immobilized peroxidase starting at +600 mV and reaching a maximum at about 0 mV vs. SCE. The enzyme layer is stabilized by the addition of bovine serum albumin and cross-linking with glutaraldehyde. A glucose sensor based on glucose oxidase is presented.