A superoxide anion biosensor based on direct electron transfer of superoxide dismutase on sodium alginate sol-gel film and its application to monitoring of living cells.

The direct electron transfer of superoxide dismutase (SOD) was greatly facilitated by sodium alginate (SA) sol-gel film with the formal potential of 0.14 V, which was just located between O(2)(•-)/O(2) and O(2)(•-)/H(2)O(2). The preparation of the SOD/SA modified electrode was simple without any mediators or promoters. Based on bimolecular recognition for specific reactivity of SOD/SA toward O(2)(•-), the SOD modified electrode was utilized to measure O(2)(•-) with good analytical performance, such as low applied potential (0 V), high selectivity (no obvious interference), wide linear range (0.44-229.88 μM) and low detection limit (0.23 μM) in pH 7.0 phosphate buffer solution. Furthermore, it could be successfully exploited for the determination of O(2)(•-) released from living cells directly adhered on the modified electrode surface. Thus, the proposed O(2)(•-) biosensor, combining with the properties of SA sol-gel film, provided a novel approach for protein immobilization, direct electron transfer study of the immobilized protein and real-time determination of O(2)(•-) released from living cells.