Aqueous polythiophene electrosynthesis: A new route to an efficient electrode coupling of PQQ-dependent glucose dehydrogenase for sensing and bioenergetic applications

In this study, polythiophene copolymers have been used as modifier for electrode surfaces in order to allow the immobilization of active pyrroloquinoline quinone dependent glucose dehydrogenase (PQQ-GDH) and to simultaneously improve the direct electrical connection of the enzyme with the electrode. Polymer films are electrosynthesized in aqueous solution without the need of surfactants onto carbon nanotubes modified gold electrodes from mixtures of 3-thiopheneacetic acid (ThCH2CO2H) and 3-methoxythiophene (ThOCH3) using a potentiostatic pulse method. Polythiophene deposition significantly improves the bioelectrocatalysis of PQQGDH: the process starts at -200 mV vs. Ag/AgCl and allows well-defined glucose detection at 0 V vs. Ag/AgCl with high current density. Several parameters of the electro-polymerization method have been evaluated to maximize the anodic current output after enzyme coupling. The polymer deposited by this new procedure has been morphologically and chemically characterized by different methods (SEM, EDX, FT-IR, UV-Vis, XPS and Raman spectroscopy). The bioelectrocatalytic response towards increasing glucose concentrations exhibits a dynamic range extending from 1 mu M to 2 mu M. The low applied potential allows to avoid interferences from easily oxidizable substances such as uric acid and ascorbic acid. Short and long-term stability has been evaluated. Finally, the PQQ-GDH electrode has been coupled to a bilirubin oxidase (BOD)-and carbon nanotube-based cathode in order to test its performance as anode of a biofuel cell. The promising results suggest a further investigation of this kind of polymers and, in particular, the study of the interaction with other enzymes in order to employ them in building up biosensors and biofuel cells.