Electropolymerization of catecholamines after laccase-catalyzed preoxidation to efficiently immobilize glucose oxidase for sensitive amperometric biosensing

We describe here the electropolymerization of catecholamines preoxidized by laccase (Lac) catalysis as a novel protocol to efficiently immobilize glucose oxidase (GOx) at Au electrodes for sensitive amperometric biosensing of glucose. The rates of Lac-catalyzed polymerization in aqueous solutions were found to follow the order of dopamine (DA) > l-noradrenaline (NA) ≫ epinephrine (EP), as examined by visual inspection, UV–vis spectrophotometry, and electrochemical techniques. Electrochemical quartz crystal microbalance (EQCM) was used to monitor the electropolymerization of catecholamines preoxidized by Lac catalysis in the absence and presence of GOx. The GOx immobilized in the poly(l-noradrenaline) (PNA) matrix retained a high enzymatic specific activity, as quantified by UV–vis spectrophotometry and EQCM methods. The PNA-involved enzyme electrode displayed a glucose-assay sensitivity of 38 μA cm−2 mmol−1 L and a limit of detection of 0.4 μmol L−1 at 0.7 V vs. SCE under optimal conditions, being more sensitive than that prepared via preoxidation-free conventional electropolymerization. Sensitivity enhancement was also obtained when DA or EP was used for similar polymerization and GOx-immobilization, and the DA and NA polymer substrates gave almost identical glucose-biosensing performance that were much better than the EP one, suggesting that the NA polymer substrate is a good alternative to the well-recognized DA one. The proposed strategy of high efficiency and universality may have application potentials in many fields, such as biosensing, biocatalysis, and biofuel cells.