Amperometric Tyrosinase Biosensor Using Enzyme‐Labeled Au Colloids Immobilized on Cystamine/Chitosan Modified Gold Surface

An amperometric tyrosinase biosensor for phenolic compounds was developed via a simple and effective immobilization method. Tyrosinase‐labeled nano‐Au colloids were immobilized on chitosan layer, which was fixed on cystamine‐modified gold electrode through the glutaraldehyde crosslinking. The tyrosinase retained its bioactivity well in such an immobilization matrix. Phenolic compounds were determined by the direct reduction of biocatalytically generated quinone species at −100 mV vs. SCE. The parameters of the fabrication process and the variables of the experimental conditions for the enzyme electrode were optimized. The resulting sensor exhibited excellent reproducibility, stability and sensitive response. The detection limit of 0.32 µmol L−1 catechol, 0.60 µmol L−1 phenol, and 0.18 µmol L−1 p‐cresol were obtained and 75% of the activity was maintained after 2 weeks.