Electropolymerization of thionine in neutral aqueous media and H2O2 biosensor based on poly(thionine)

A novel two-step method is presented for the electropolymerization of thionine in neutral phosphate buffer solutions containing 1 x 10(-4) M thionine on glassy carbon electrode surfaces. The formation of the PTH film is dependent on the preanodization voltage and occurs only on a GCE surface, The preanodization operation is critical. During this period, a large amount of positive charge can be accumulated on the GCE surface and is used to create the thionine cation radical for the electropolymerization of thionine. The poly(thionine) (PTH)-modified electrode obtained in this manner has a golden, fairly even film, which is firm and permanent. Strong treatment in an ultrasonic bath for 20 min does not affect the voltammetric redox peaks of PTH. The E-0' decreases by 55 mV/pH between pH 6 and 8 for the immobilized PTH, which is close to the expected Nernstian value of 59 mV for a two-electron, two-proton process. The PTH-modified electrodes show linear dependence of peak current with scan rate within the range of 20 to 100 mV s(-1). A H2O2 biosensor was fabricated by using Nafion membranes with enzyme. The catalytic reaction towards H2O2 reduction occurring on the H2O2 sensor in the presence of 1 mM H2O2 demonstrated that the film of PTH can effectively shuttle electrons between the redox center of HRP and the base electrode. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.