Quantitative impedimetric immunosensor for free and total prostate specific antigen based on a lateral flow assay format

Abstract A disposable immunosensor approach for the determination of free and total prostate specific antigen (f-PSA, t-PSA) is described. The system combines impedance measurements of a degradation process taking place on pH sensitive polymer-coated electrodes with lateral flow immunostrips based on a non-competitive “sandwich” assay format and the use of a monoclonal anti-PSA urease conjugate as a tracer. Immunostrips were prepared using Nitrocellulose membranes coated with either anti-f-PSA or anti-t-PSA antibodies, together with a backing material containing both sample-addition and sink pads. Each immunostrip was inserted into a cartridge and placed in intimate contact with a polymer-coated electrode system. Following the completion of the immunoassay on the strip, hydrolysis of urea by the urease label generated ammonia and a consequent localised increase of pH, which, in turn, caused the degradation of the polymer layer on the electrode and thus a change in the capacitance of the system. The degree of degradation of the polymer could thus be related to the amount of analyte in the sample. This device exhibited an assay time of less than 20 min and the required sensitivity to determine both forms of PSA in serum. These results build up the first step for the development of a fully integrated PSA immunosensor that could be used as a front-line screen in the diagnosis of prostate cancer.