Fabrication of electrodes for highly sensitive detection of a superoxide anion radical by electropolymerization of thienylporphyrins in the presence of thiophene and application to active oxygen sensors

The superoxide anion radical (O₂^-·) has attracted much attention in many fields of biology since it was realized that superoxide anions are produced in significant quantities in various parts of biological systems, from microorganisms to mammals. Therefore, quantitative measurements of O₂^-· in vivo are important for clarifying such relationships under various conditions. However, in most cases, the biological significance and the mechanism of the generation O₂^-· are not yet well understood. We have developed an O₂^- · sensor composed of a thin film of 1-methylimidazole-coordinated iron meso-tetra(3-thienyl)porphyrin ([Fe(im)₂(ttp)]Br) for the electrochemical detection of O₂^-· The microsensor displayed high selectivity and activity for the oxidation of O₂^-· and showed a linear relationship between the current and the O₂^-· concentration. In this research, the improvement of the sensor sensitivity was accomplished by mixing polythiophene as the electroconductive polymer on the electrode surface. The sensors were prepared using various compositions of [Fe(im)₂(ttp)]Br and thiophene as the monomers. During in vitro tests, O₂^-· was generated as an intermediate during the oxidation of xanthine by xanthine oxidase (XOD), for detection using this sensor. The electric conductivity of the polymer increased, accompanied by the increase in the amount of the thiophene unit. The highest sensitivity was obtained at a monomer composition of [Fe(im)₂(ttp)]Br : thiophene = 1:8.