Sensors and Actuators B 151 (2010) 30–38 Contents lists available at ScienceDirect Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb Electropolymerization of catecholamines after laccase-catalyzed preoxidation to efficiently immobilize glucose oxidase for sensitive amperometric biosensing Yunyong Li a , Yueming Tan a , Wenfang Deng a , Qingji Xie a,∗ , Yingying Zhang a , Jinhua Chen b , Shouzhuo Yao a,b a Key Laboratory of Chemical Biology and Traditional Chinese Medicine Research (Ministry of Education), College of Chemistry and Chemical Engineering, Hunan Normal University, Changsha 410081, PR China b State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082, PR China article info Article history: Received 25 June 2010 Received in revised form 15 September 2010 Accepted 25 September 2010 Available online 20 October 2010 Keywords: Electropolymerization of catecholamines preoxidized by laccase (Lac) catalysis Enzyme immobilization Glucose biosensing Electrochemical quartz crystal microbalance abstract 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 ampero- metric 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 spectrophotome- try and EQCM methods. The PNA-involved enzyme electrode displayed a glucose-assay sensitivity of 38 A cm -2 mmol -1 L and a limit of detection of 0.4 mol L -1 at 0.7 V vs. SCE under optimal condi- tions, 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. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Amperometric enzyme electrodes are important bioelectroana- lytical devices of high academic and industrial interest [1,2]. Robust immobilization of reactive enzymes at high activity and high load on the electrode is very important in this field, and many rele- vant techniques have been reported [3–6], including adsorption, covalent crosslinking, and entrapment in various materials (e.g. polymers, redox gels, sol–gel-derived glasses, and carbon pastes). Electropolymerization and appropriate chemical polymeriza- tion of various monomers in aqueous solutions containing the target enzyme(s) have been widely used to entrap the enzyme(s) in the synthesized polymers for biosensing [7–10]. An enzyme film electrode can be readily prepared by the electropolymer- ization protocol, but the chemical polymerization protocol often requires an additional and special step for modification of the ∗ Corresponding author. Tel.: +86 731 88865515; fax: +86 731 88865515. E-mail address: xieqj@hunnu.edu.cn (Q. Xie). chemically synthesized polymeric biocomposites on the electrode surface (e.g. cast or spin coating). Hence, by precisely controlling the electrochemical parameters of the electropolymerization proto- col, one can control the enzyme-film thickness more conveniently than using the chemical polymerization protocol. However, the electropolymerization protocol has the disadvantages that (1) the enzyme load in the electrosynthesized thin-layer polymers is lim- ited even in the conducting polymer cases [11], since the electrode conductance and reactivity will be gradually decreased and thus the growth of a very thick polymer film is difficult, but the chemi- cal polymerization starts from the chemical reactions and is free of the electrode-reactivity problem, thus the high enzyme load in the chemically synthesized polymer precipitates can be obtained; (2) enzyme immobilization is achieved through the interfacial code- position of the enzyme molecules with the growing polymer on the electrode surface, probably leading to limitation of the 3-D conformational freedom of deposited enzyme molecules; thus, the enzymes immobilized by the electropolymerization protocol are easier to partially loss their biological activities [11–13]. Obviously, it is interesting and useful to integrate the above advantages of the 0925-4005/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2010.09.061