Electrochemical oxidation of NADH on sol-gel derived, surface renewable, non-modified and mediator modified composite-carbon electrodes

The electrochemical oxidation of the cofactor, dihydronicotinamide adenine dinucleotide was studied on sol-gel derived, polishable, ceramic-carbon electrodes (CCEs), in phosphate buffer of pH 7.3. NADH was found to undergo an apparently irreversible, two-electron oxidation in the available range of potentials. Cyclic voltammetric studies at high sweep rates revealed a prewave due to the adsorption of the oxidation product, NAD⁺. The prewave was found to be suppressed when the surface was adsorbed with NAD⁺, prior to initiating the voltammetric scan. Steady state sensing of the cofactor at high overpotentials of 0.3 and 0.5 V was complicated by the adsorption process. However, CCEs have the advantage of sensing NADH at low potentials of 0.15 V vs. Ag|AgCl|KCl (satd.) where the interferences due to adsorption were found to be greatly minimized. A comparison of glassy carbon and CCEs reveals a shift of the onset potential of oxidation by more than 0.3 V and higher sensitivity of the CCE. Bulk modification of the CCEs by incorporation of Meldola's blue into the sol-gel precursors was found to reduce the overpotential needed for NADH sensing to -0.2 V. Stability of the signal at low overvoltages in the continuous operation mode was found to be good. The surface renewability of the CCEs by mechanical polishing revealed less than 8% relative standard deviation for successive surface renewals of the blank and mediator modified electrodes.