a-Naphthoyl Nile blue (NNB) is a new electron-transfer mediator. It can be strongly adsorbed on graphite to make modified electrodes. The immobilized NNB exhibits relatively reversible redox behavior in the potential region from -0.5 to +0.6V (vs. SCE), 2 electrons and 2 protons taking part in the overall reaction. In pH 7.0 buffer solution, the surface standard potential E0' is -170 mV, and apparent electron-transfer rate constant ks is 3 s-1. NNB-modified electrodes show significant catalytic effects on electrochem. oxidation of dihydrocoenzyme NADH, making oxidation overpotential decrease by 550 mV. The electrocatalytic oxidation of NADH obeys EC mechanism, where the catalytic reaction is the rate-detg. step with a rate constant of 3 ?103 dm3/mol/s. In neutral and weakly basic solns., NNB is more stable than the other mediators; hence, it appears to be promising for practical applications.

Key words: STABILITY, OXIDATION REDUCTION REACTION, DEHYDROGENASE, NUCLEOSIDE DIPHOSPHATE, DISK ELECTRODES, CHEMICAL MODIFIED ELECTRODE, ELECTRO-CATALYSIS, CATALYTIC OXIDATION, CHARGE TRANSFER, NAPHTHALENECARBOXYLIC ACID P