Electrochemical cysteine biosensor based on the selective oxidase–peroxidase activities of copper, zinc superoxide dismutase

Abstract

A new cysteine (CySH) biosensor was developed based on its oxidase–peroxidase activities with copper, zinc superoxide dismutase (SOD1). The biosensor comprising of SOD1 coimmobilized with horseradish peroxidase (HRP) on polypyrrole (PPy)-platinum (Pt) electrode was characterized by cyclic voltammetry. The bienzymatic electrode exhibited an electrochemical response with cysteine due to the bicarbonate-dependent peroxidase activity stimulated by thiol oxidase activity of SOD1. Among the thiols, viz., CySH, HCY and GSH, CySH only showed a remarkable amplification of current. Thus, the biosensor is CySH selective. The electrode linearly responded to cysteine concentrations up to 500μM with a detection limit of 10μM. The CySH biosensor is highly stable, selective and reproducible, making it suitable for analytical purposes. Using this biosensor, the levels of CySH present in commercially available l-CySH dietary supplement tablets, serum and urine were estimated.