Labeless Immunosensor Assay for Prostate Specific Antigen with Picogram per Milliliter Limits of Detection Based upon an ac Impedance Protocol

This paper describes the development of labeless immunosensors for the prostate cancer marker prostate specific antigen (PSA). Poly(1,2-diaminobenzene) was electrodeposited onto screen-printed carbon electrodes, and this modified surface was sonochemically ablated to form a microelectrode array. Polyaniline was electropolymerized within these pores to form a microarray of conductive polyaniline protrusions. Two methods were utilized to immobilize antibodies for prostate specific antigen (APSA). The first involved entrapment of APSA during electropolymerization of the polyaniline. The second utilized a polyaniline array as a substrate to immobilize a biotinylated APSA using a classical avidin−biotin affinity approach. Microelectrode arrays were interrogated using ac impedance protocols before and following exposure to PSA solutions. Our preliminary results show that concentration/ac response relationships were recorded over very different ranges; sensors fabricated using an affinity approach exhibited detection limits 1000 times lower than those formulated by the entrapment method. This demonstrates that assembly protocols have major effects on immunosensor performance.