Construction of a thin-film immunosensor with self-doping polyaniline modified electrode for human serum albumin detection

A competitive immunosensor, based on the indium tin oxide (ITO) electrode coupling a thin film of self-doping polyaniline (SPANI), was fabricated for the detection of human serum albumin (HSA). By properly preparing the aniline doped with o-aminobenzenesulfonic acid, the morphology of the SPANI was shaped into microsphere form. When SPANI coated on the ITO glass surface as the electrode, a high conductivity, high biocompatibility and high stability sensor could be obtained attributed to the high surface area of SPANI microsphere. By coupling HSA in SPANI layer and measuring the differential pulse voltammograms, a competitive immunoassay, capable of HSA concentration determination, was constructed. To enhance the sensitivity of the immunosensor, a secondary antibody conjugated with colloidal gold were also applied. The optimal conditions for the detection were found as follows: the immobilized albumin of 250 μg/mL, the anti-albumin of 20 μg/mL and the secondary antibody conjugated with colloidal gold (CG) of 5 μg/mL. The detection has a linear range from 10 to 200 μg/mL and a detection limit of 1 μg/mL without using CG. In contrast, under the use of CG, the linear range was from 0.5 to 200 μg/mL with a detection limit of 413 ng/mL.