Electrochemical sensor for superoxide anion radical using polymeric iron porphyrin complexes containing axial 1-methylimidazole ligand as cytochrome c mimics

A needle‐type electrochemical sensor for the facile detection of superoxide anion radical (O 2−.) was devised using an electrodeposited film of a polymeric porphyrin complex attached to a carbon microelectrode which was placed in a stainless steel 18G needle tube as an auxiliary electrode. The sensing element was prepared by means of electropolymerization of bromoiron(III) meso‐ tetra(3‐thienyl)porphyrin in the presence of 1‐methylimidazole in CH2Cl2 containing 100 mM tetrabutylammonium perchlorate (TBAP) as a supporting electrolyte, which gave a smooth film of the corresponding polymer. The film was electrochemically active to give a redox response near −0.05 V versus Ag/AgCl due to the iron(II/III) couple. The microsensor was applied to detect O 2−. produced by xanthine oxidation catalyzed by xanthine oxidase. The amperometric response for O 2−. was monitored at an electrode potential of 0.5 V versus the auxiliary electrode in a 10 mM phosphate buffer. The microsensor displayed a high catalytic activity for the oxidation of O 2−. and showed a linear relationship between the current and the O 2−. concentration. Axial coordination of an imidazole ligand to the iron porphyrin center enhanced selectivity for O 2−. by impeding the undesired coordination of H2O2 that resulted from the dismutation of O 2−.. Copyright © 2005 John Wiley & Sons, Ltd.