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, D(ct), of (1.6±0.2)x 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)x10^-4cm 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.