Disposable Noncompetitive Immunosensor for Free and Total Prostate-Specific Antigen Based on Capacitance Measurement

This work reports on the successful integration of a one-step lateral flow immunoassay format and impedance detection of the specific affinity event using an electrochemical transducer coated with a pH-sensitive polymer layer. This approach was particularly applied to the development of a rapid single-use immunosensor for the sensitive detection of free and total prostate-specific antigen (f-PSA, t-PSA) tumor marker. Strips of nitrocellulose membrane were coated with appropriate antibodies to f-PSA and t-PSA and used as solid supports for the performance of noncompetitive immunoassays where PSA was allowed to react with both immobilized anti-PSA antibody and anti-PSA urease enzyme conjugate for less than 1 min. An additional piece within the device consisting of a storage blister filled with a urea solution allowed the rapid washing of unbound species from the membrane strips and simultaneous urea hydrolysis catalyzed by the bound urease conjugate in an automatic fashion. The hydrolysis of urea increased the pH of the reaction media, which in turn induced a breakdown of the polymer layer on the transducer and a consequent measurable change in capacitance of the system. This was easily recorded at a given frequency over a 30-min period. Overall, we describe a one-step immunosensor prototype that exhibits enough sensitivity to detect both forms of PSA at concentration levels down to 3 ng/mL. With the possibility of being portable and considering its ease of use, robustness, and simplicity, this device has great potential as a tool for the screening and early detection of prostate cancer.