Third-generation superoxide anion sensor based on superoxide dismutase directly immobilized by sol-gel thin film on gold electrode

A third-generation biosensor for superoxide anion (O-2(.-)) was developed based on superoxide dismutase (SOD) immobilized by thin silica-PVA sol-gel film on gold electrode surface. A rapid and direct electron transfer of SOD in the thin sol-gel film at the gold electrode was realized without any mediators or promoters. The characterization of the SOD electrodes showed a quasi-reversible electrochemical redox behavior with a formal potential of 80 + 5 mV (versus SCE) in 50 mmol 1(-1) phosphate buffer solution (PBS), pH 7.0. The heterogeneous electron transfer rate constant was evaluated to be about 2.1 s(-1). The anodic and cathodic transfer coefficients are 0.6 and 0.4, respectively. Based on biomolecular recognition for specific reactivity of SOD toward O-2(.-), the SOD electrode was applied to a sensitive and selective measurement Of 02*- with the low operation potential (-0.15 V versus SCE) in phosphate buffer solution, pH 7.0. The amperometric response was proportional to O-2(.-) concentration in the range of 0.2-1.6 mumol 1(-1) and the detection limit was 0.1 mumol 1(-1) at a signal-to-noise ration of 3. The preparation of SOD electrode is easy and simple. The uniform porous structure of the silica-PVA sol-gel matrix results in a fast response rate of immobilized SOD and is very efficient for stabilizing the enzyme activity. (C) 2003 Elsevier B.V. All rights reserved.