Dehydrogenase-modified carbon-fiber microelectrodes for the measurement of neurotransmitter dynamics. 1. NADH...

The voltammetry of NADH has been characterized at carbon-fiber microelectrodes at scan rates up to 100 V/s. Electrochemical pretreatment of the electrode dramatically changed the properties of the modified electrode. Anodic pretreatment of the surface resulted in an adsorptive wave for NADH oxidation, while less adsorption was evident under more moderate conditions. The pH of the buffer used for the anodization played a critical role in determining the voltammetric peak shape. Oxidation of NADH at slow scan rates (< 10 V/s) fouled the electrode. In contrast, consistent and reproducible voltammetry of NADH was observed at faster scan rates (100 V/s). This voltammetric measurement was used to monitor NADH generated during the oxidative deamination of glutamate catalyzed by glutamate dehydrogenase. A 150-microns-l.d. microdialysis fiber was used to entrap the enzyme near the microelectrode tip, forming the dehydrogenase-modified carbon-fiber microelectrode.