A sensor for superoxide in aqueous and organic/aqueous media based on immobilized cytochrome c on binary self-assembled monolayers

A method for the electrochemical detection of superoxide radical was developed, based on cytochrome c (cyt c) immobilized on the binary self-assembled monolayers (SAMs) of thioctic acid (T-COOH) and thioctic amide (T-NH2) on gold electrode. The sensor works by electrochemically detecting cyt c reduced by the superoxide radical generated by a xanthine–XOD system. The electrochemical properties of immobilized cyt c were investigated in aqueous buffer and in a mixture of aqueous and organic solvents. The interaction of superoxide radical with the modified electrode was characterized in phosphate buffer solution (PBS) and in the mixtures of both PBS and dimethyl sulfoxide (DMSO) and PBS and glycerol (Gly). The results showed that the sensors responded immediately to superoxide radical in PBS and gave a steady-state anodic current within 10 s during the generation of superoxide radical. In 40% DMSO and in 30% Gly solution, the current response reached a steady-state anodic current within 20 s. The sensor could also be used to estimate superoxide dismutase (SOD).