Superoxide radical sensing using a cytochrome c3 immobilized conducting polymer electrode

A biosensor based on cytochrome c(3) (cyt c(3)) has been introduced to detect and quantify superoxide radical (O-2(center dot-)). Cyt c(3), isolated from the sulfate-reducing bacterium (Desulfovibrio vulgaris Miyazaki F. strain), and its mutant were immobilized onto a conducting polymer coated electrodes by the covalent bonding with carbodiimide chemistry. The immobilization of cyt c(3) was investigated with quartz crystal microbalance, electrochemical impedance spectroscopy, and cyclic voltammetric studies. The CVs recorded for cyt c(3) and a mutant modified-electrodes showed a quasi-reversible behavior having the formal potential of about -471 and -476 mV (versus Ag|AgCl), respectively, in a 0.1 M phosphate buffer solution (pH 7.0). The modified electrodes showed the surface controlled process and the electron transfer rate constants (k(s)) were evaluated to be 0.47 and 0.51 s(-1) for cyt c(3) and mutant modified electrodes, respectively. A potential application of the cyt c(3) modified electrode was evaluated by monitoring the bioelectrocatalytic response towards the O-2(center dot-). The hydrodynamic range of 0.2-2.7 mu mole L-1 and the detection limit of 0.05 mu mole L-1 were obtained. (C) 2007 Elsevier B.V. All rights reserved.