Bioelectrocatalysed reduction of nitrate utilizing polythiophene bipyridinium enzyme electrodes

Enzyme electrodes in several configurations including the enzyme nitrate reductase are applied in the bioelectrocatalysed reduction of nitrate to nitrite. One enzyme electrode configuration includes the physical immobilization of nitrate reductase in a polythiophene-bipyridinium matrix formed by electropolymerization of 1-methyl-1′-(3-thiophene-3-yl)-pentyl-4,4′-bipyridinium-bis-hexafluorophosphate. The bipyridinium units of the polymer act as electron mediators between the electrode and the enzyme. The concentration of bioelectrogenerated nitrite depends on the concentration of nitrate in the electrolyte solution. A calibration curve representing the rate of nitrite formation as a function of nitrate concentration in the electrolysis cell allows quantitative analysis of nitrate in aqueous solutions. Two other enzyme-electrode configurations include copolymerization of thiophene-bipyridinium and thiophene-3-acetic acid, onto a gold electrode and layered deposition of two polymers composed of thiophene-bipyridinium and thiophene-3-acetic acid onto the electrode. Covalent linkage of the enzyme nitrate reductase to the carboxylic acid residues of the different polymer matrices results in active enzyme electrodes for bioelectrocatalysed reduction of nitrate to nitrite.