Electrochemical polyaniline/polypyrrole composite film with novel nanostructure and high biosensitivity

Yunan Cheng Yunan Cheng,Gang Wu Gang Wu,Gustaaf Borghs Gustaaf Borghs,Mang Wang Mang Wang,Hong-Zheng Chen Hong-Zheng Chen

doi:10.1109/aoe.2007.4410769

Abstract

Conductive polymer, such as polypyrrole (PPY) and polyaniline (PANI), have shown a special ability to rapidly and reversibly switch between different oxidation states [1,2], which plays a critical role in biocommunication. In addition, various biomolecules can be incorporated into conducting polymer by electrochemical polymerization. These two abilities make conducting polymers potential candidates for application in the area of biosensors [3,4]. The synthesis of conducting polymer films thus has recently been an increasingly important subject of intensive research. [5,6] PPY is the most thoroughly investigated one among various conducting polymers for biological applications because of its high electrical conductivity in wide range of pH values, flexible method of preparation, ease of surface modification, excellent environmental stability, ion exchange capacity and biocompatibility [3,7-9,10-11] . But one of the properties that restrict the development of electrochemically synthesized PPY film is its flat surface with limited surface area. This has been overcome to some extent by template methods. Method of polymerizing pyrrole within porous materials was used to enhance the surface area of PPY[10-11]. PPY films with sub-100-nm features were synthesized on atomically flat surfaces using adsorbed surfactant molecules as templates [12]. Arrays of PPY dots (80-180 nm diameter) were prepared by using diblock copolymer surface micelle arrays as the reaction template[13]. PPY nanotubes with average pore diameter of 6 nm were synthesized by using FeC 3 oxidant and V 2 O 5 nanofibers as the sacrificial template [14]. In addition, the method of preparing multilayer polymer composite film on the base of PANI[15], polythiophene [PMET-PPY], polysiloxane[16], etc., was also employed to enhance the surface area of PPY and the continuous films with microscaled structure were obtained. While, few researchers reported the synthesis of continuous PPY films with nanostructrural surface morphology with a templateless method. In this study, we synthesized PANI/PPY bilayer composite films on ITO substrate by two-step constant potential electrochemical method. Our ultimate goal is to produce continuous PPY films with large surface area to ease the immobilization of enzyme and to enhance the concentration of enzyme redox centers. The PPY and PANI films were also separately prepared on ITO for a comparison. Scanning Electron Microscope and Atomic Force Microscope were used to observe the surface morphology. The PANI/PPY bilayer composite film on ITO was found to be made up of micro/nano domains, which may contribute in a remarkable increase of the surface area of the film. The H 2 O 2 amperometric biosensor was constructed by coating horseradish peroxidase (HRP) on the PANI/PPY bilayer composite film. Compared with the PPY or PANI film on an ITO substrate, the HRP-containing micro/nano structural PANI/PPY bilayer composite film could act as highly sensitive sensor for the enzymatically generated H 2 O 2 . The proposed biosensor permitted reliable determinations of H 2 O 2 by chronoamperometry analysis. The detection limit and sensitivity were found to be on the range of 0.3 -1.0 mmol/1 and 38.81 mA cm -1 mol -1 , respectively. This work was financially supported by the National Natural Science Foundation of China (No.50433020, 50520150165 and 50673083). The authors also would like to thank the financial support from the Research Fund for the Doctoral Program of Higher Education in China (No. 20060335078).

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