245 1040-8347/02/$.50 © 2002 by CRC Press LLC Critical Reviews in Analytical Chemistry, 32(3):245–252 (2002) Application of Polypyrrole for the Creation of Immunosensors A. Ramanaviciene 1 and A. Ramanavicius 1,2 * 1 Laboratory of Ecological Immunology, Institute of Immunology, Molètu c pl., 2600, Vilnius, Lithuania; 2 Department of Analytical and Environmental Chemistry, Vilnius University, 2009, Vilnius, Lithuania. * e-mail: arman@bchi.lt ABSTRACT: This review focuses on the use of conducting polymer (CP) films in electrochemical affinity sensors and emphasizes innovative designs and unique applications of immunosensors. The review covers some aspects in the application of polypyrrole (Ppy) for the creation of immunosensors. Polypyrrole film fabrication methods like solvent casting, adsorption, and electropolymerization are presented. The focus, is on electrochemically synthesized Ppy as very promising material for the formation of miniaturized electrochemical immunosensors. Polypyrrole films implemented in various capacities in amperometric, conductometric, and potentiometric immunosensor design are reviewed. The acceptance of immobilization and detection approaches used recently in affinity sensors with critical analysis applied in certain techniques is discussed. The biologically active components (BAC) used for the creation of polypyrrole-based immunosensors are described briefly. Some future trends in the development of polypyrrole-based immunosensors are predicted, as well as possible directions discussed. KEY WORDS: conducting polymers, polypyrrole, immunosensors, immobilization, antibody. I. INTRODUCTION The quantitative analysis of selected compo- nents from complex biological and environmen- tal samples traditionally has been achieved by the time-consuming and expensive combination of highly sophisticated chromatographic and spec- troscopic techniques. 1 The requirement for the real-time monitoring of given analytes in medi- cal, industrial, and environmental applications has meant that alternatives to bulky laboratory-based procedures had to be found, especially in the case of in vivo analysis. 2 In recent years advances in the miniaturization and construction of electronic components and the fast response times offered by electrochemical tech- niques has created a demand for fast bio- and immuno-sensing information-collecting systems that can be easily integrated into technology, such as microprocessor-based electronics. 3 For these applications, biosensors, immunosensors, and biomimetic affinity sensors are required, as they are suitable for mass production. The biosensors and immunosensors are usually defined as sensing devices consisting of a biological recognition ele- ment in intimate contact with a suitable transducer, which is able to convert biological recognition reaction or eventually the biocatalytic process into a measurable electronic signal. 4 Immunosensors and affinity sensors based on molecularly imprinted polymers or high-affinity RNA aptamers are ana- lytical devices that detect the binding of analyte by coupling immunochemical reaction to the modi- fied surface of the device known as a transducer. 5 They are used mainly in areas where both high selectivity and high sensitivity are required. 6 Immunosensors have been the subject of increas- ing interest mainly because of their potential appli- cation as an alternative immunoassay technique in areas such as clinical diagnostics and environmen- tal control. 7 The conversion of the binding event into a measurable signal in particular at low con- centrations, the regenerability, and the reusability are, among other topics, major challenges in immunosensor development research. 8 Piezoelec- tric quartz crystal microbalance (QCM), surface