An Electrochemical Immunosensor Based on Poly(Thionine)-Modified Carbon Paste Electrode for the Determination of Prostate Specific Antigen

We have attempted to fabricate an electrochemical immunosensor for prostate specific antigen (PSA) using the amine groups in poly(thionine) film to which anti-PSA antibody can be covalently bound using glutaraldehyde as a bifunctional reagent. The poly(thionine) film was deposited on a carbon paste electrode after the electropolymerization of thionine monomers. Detection of the PSA/anti-PSA reaction was performed using polyclonal antibodies conjugated with HRP. The catalytic reduction current was then measured in the presence of H2O2. The poly(thionine) film effectively shuttled electrons between the redox center of HRP and the electrode surface. On the other hand, the value of the current correlated with the amount of HRP placed near the electrode surface which was in turn proportional to the amount of the PSA bound to the sensor surface. Since more than one polyclonal antibody generally link to each antigen, a large amount of HRP accumulates near the electrode surface leading to the signal amplification. Different experimental parameters were also optimized for higher sensitivity. The proposed immunosensor exhibited two linear relationships between PSA concentration and the electrochemical signal in the ranges of 3-15 and 15-100 ng/mL with a detection limit of 0.093 ng/mL. The accuracy of the presented biosensor was confirmed using a certified human serum.