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) 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 produced by xanthine oxidation catalyzed by xanthine oxidase. The amperometric response for O 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 and showed a linear relationship between the current and the O concentration. Axial coordination of an imidazole ligand to the iron porphyrin center enhanced selectivity for O by impeding the undesired coordination of H₂O₂ that resulted from the dismutation of O. Copyright © 2005 John Wiley & Sons, Ltd.