Direct Electron Transfer of Polyphenol Oxidase on Carbon Nanotube Surfaces: Application in Biosensing

In this work, the adsorption of polyphenol oxidase (PPO) on single-walled carbon nanotubes (SWCNTs) and its electrocatalytic behavior were investigated. To construct the biosensor, polyphenol oxidase was immobilized on the SWCNTs/GC electrode. Scanning electron microscope (SEM) and atomic force microscope (AFM) images were obtained for used SWCNTs. Direct electrochemistry of immobilized PPO was extensively investigated. Immobilized enzyme displayed a couple of stable redox peaks with a formal potential (E°´) of 0.102 V with respect to reference electrode in 0.05 M phosphate buffer solution (pH 7.0). The experimental results demonstrated that the immobilized PPO on SWCNTs could catalyze the oxidation of HCA. Additionally, apparent Michaelis-Menten constant (Km), a reflection of enzymatic affinity, for HCA and stability of PPO/SWCNTs/GC electrode were estimated. The proposed method exhibits good sensitivity, stability and reproducibility.