A needle-type electrochemical sensor for the facile detection of superoxide anion radical (O 2 À.) 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) mesotetra(3-thienyl)porphyrin in the presence of 1-methylimidazole in CH 2 Cl 2 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 À0.05 V versus Ag/AgCl due to the iron(II/III) couple. The microsensor was applied to detect O 2 À. produced by xanthine oxidation catalyzed by xanthine oxidase. The amperometric response for O 2 À. 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 À.and showed a linear relationship between the current and the O 2 À. concentration. Axial coordination of an imidazole ligand to the iron porphyrin center enhanced selectivity for O 2 À. by impeding the undesired coordination of H 2 O 2 that resulted from the dismutation of O 2 À..
5-(3-Thienyl)-10,15,20-triethyl-21H,23H-porphine (H 2 (ttep)) was synthesized and characterized. Oxidative polymerization of H 2 (ttep) gave a novel oligomeric porphyrin linked at the 2,5-positions of the thienyl group. Electric conductivity of 4 Â 10 À1 S/cm after I 2 doping indicated that the oligomer had a p-conjugated structure with a delocalization of p electrons over the thienylene backbone. PM3 calculations revealed a low HOCO-LUCO gap, which was consistent with the relatively high electric conductivity. Regioregular (head-to-tail) structure was inferred from spectroscopic and calculational results. The pendant porphyrin groups formed a regular J-type array along the thienylene backbone, which was indicated by a significant red shift of the Soret band maximum. Figure 6. (a) UV-vis spectra of H 2 (ttep) (3.5 Â 10 À7 mol/L) (solid curve) and undoped 1 (3.5 Â 10 À7 mol unit/L) (dotted curve) in DMSO. Optical path length was 1 cm. (b) UV-vis spectrum for the electropolymerized film of 1 on an ITO electrode. [Color figure can be viewed in the online issue, which is available at www.interscience. wiley.com.] 5410 OYAIZU ET AL.
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