[Os(bpy)2(PVI)10Cl]Cl polymer-modified carbon fiber electrodes for the electrocatalytic oxidation of NADH

Carbon fiber microelectrodes modified with [Os(bpy)2(PVI)10Cl]+ films are described, where bpy is 2,2′-bipyridine and PVI is a poly(vinylimidazole) polymer. The electrochemical properties of the polymer-modified microelectrodes were studied using cyclic voltammetry, chronoamperometry and normal pulse voltammetry. A charge transport diffusion coefficient, Dct, of (1.6 ± 0.2) × 10−9 cm2 s−1 was estimated for these films using chronoamperometry at a modified microdisk carbon fiber electrode. A heterogeneous electron transfer rate constant of (5.0 ± 0.5) × 10−4 cm s−1 was evaluated by normal pulse voltammetry at the microcylinder electrode. The polymer-modified microelectrodes exhibit electrocatalytic activity for the oxidation of NADH. An apparent Michaelis-Menten constant of 0.23 ± 0.02 mM for the catalytic oxidation of NADH at the osmium-modified microcylinder electrode was evaluated and compared to the value obtained at rotating-disk polymer-modified macroelectrodes. The advantages of the modified microelectrodes for monitoring NADH levels are discussed.