A CHEMICALLY MODIFIED GRAPHITE ELECTRODE FOR ELECTROCATALYTIC OXIDATION OF REDUCED NICOTINAMIDE ADENINE-DINUCLEOTIDE BASED ON A PHENOTHIAZINE DERIVATIVE, 3-BETA-NAPHTHOYL-TOLUIDINE BLUE-O

The 7-dimethylamino-2-methyl-3-naphthamido-phenothiazinium salt (3-NTB) was obtained by reacting Toluidine Blue O (TBO) and 2-naphthoyl chloride. It was adsorbed on graphite to give a chemically modified electrode (CME) with a formal redox potential of -135 mV (vs. SCE) at pH 7. The 3-NTB CME catalyses the electrochemical oxidation of the reduced co-enzyme nicotinamide adenine dinucleotide (NADH). The reaction rate between 3-NTB and NADH was evaluated from rotating disk electrode measurements. The 3-NTB CME was also mounted in a flow-through amperometric cell in a single-channel FIA system and tested as a sensor for NADH. The calibration graph was linear over almost three decades of concentration at pH 9 with a sensitivity of 13.8 mA M-1 and a detection limit of 0.2 (μM NADH with an injection volume of 50 μl. The NADH sensor showed good stability in alkaline solutions and an improved response in terms of a decrease in pH dependence compared with previously studied sensors based on graphite electrodes modified with phenoxazine derivatives. © 1990.