BIOCATALYSIS AND ELECTROCATALYSIS AT CARBON PASTE ELECTRODES DOPED BY DIAPHORASE-METHYLENE GREEN AND DIAPHORASE-MELDOLA BLUE

The electrocatalytical oxidation of dihydronicotinamide adenine dinucleotide (NADH) and ascorbic acid was investigated on carbon paste (CP) electrodes doped by diaphorase and the mediators methylene green (MG) and meldola blue (MaB). Bioelectrocatalytical oxidation of NADH proceeds at the potential 0-0.25 V versus saturated calomel electrode (SCE). K(m(app)), I(max), and sensitivity were 0.9 and 3.6 mM, 1.4 and 6.7 muA and 0.20 and 0.24 mA mM-1 cm-2 for MaB- and MG-doped CP electrodes, respectively. The biocatalytical process of NADH oxidation is not sensitive to oxygen, and optimum activity is at pH 7.3. The nonenzymatic electrocatalytical oxidation of NADH and ascorbic acid on CP electrodes doped by mediators proceeds at the same potential, and the efficiency of NADH oxidation was 50% in comparison to the biocatalytical process. Ascorbate oxidase immobilized on graphite powder was used to increase the selectivity of the electrocatalytical system of NADH oxidation over the electrochemical oxidation of ascorbic acid.