Superoxide Anion Radical Biosensor Using Self-Assembled Cysteine Monolayer on Gold Nanoparticles in Polypyrrole Matrix Facilitated Electron Transfer in Cu,ZnSOD

An electrochemical superoxide anion radical (O(2)(center dot-)) sensor was developed using Cu,ZnSOD (SOD1) immobilized in self-assembled cysteine monolayer on gold nanoparticles (GNP)-polypyrrole (PPy) modified platinum electrode. The morphologies of the PPy and GNP-PPy film on the platinum electrode characterized by scanning electron microscopy exhibited highly porous structure resulting in effective loading of SOD1 enzymes and GNP on the electrode surface. The electrochemical behavior of the biosensor investigated by cyclic voltammetry revealed that the SOD1 immobilized electrode exhibited characteristic SOD1 quasi-reversible redox peaks with a formal potential of +0.065 V versus Ag/AgCl. The biosensor displayed an excellent electrocatalytic response to the oxidation and reduction of O(2)(center dot-) generated by KO(2) and xanthine/xanthine oxidase systems. The biosensor exhibited a linear response over the O(2)(center dot-) concentration range from 0.2 to 100 mu M (r(2) = 0.9939), with a detection limit of 0.2 mu M. Thus, a combination of the self-assembled cysteine monolayer (SAM) on GNP in PPy enhanced SOD1 loading and facilitated electron transfer provided an electrochemical approach for the determination of O(2)(center dot-) levels with high sensitivity, good reproducibility and increased stability.