A New Approach to Electrochemical Immunoassays Using Conducting Electroactive Polymers

The problem of generating a rapid, sensitive and reversible electrochemical signal with antibody-antigen (Ab-Ag) interactions has previously been addressed. It was shown that the use of antibodies immobilized in conducting electroactive polypyrrole matrices, with pulsed amperometric detection, and flow injection analysis, provides a unique solution to this problem. A sub-ppm detection limit for the target protein thaumatin was obtained, and a high selectivity towards other non-target proteins was realized. These encouraging results have resulted in further scrutiny of the principle of the mechanism involved as reported in this paper. Evidence from electrochemical quartz crystal microbalance studies (EQCM) and cyclic voltammetry confirmed that a reversible mass increase was obtained in the presence of the antigen. The results showed that the application of alternating voltage waveforms induced changes in the conducting polymers such that a detectable interaction with a target analyte (antigen) was obtained in a reversible manner. Thus the detection method resulted in a reusable immunological sensor that responded within a time scale of minutes.