Electrochemical immunoassay for α-1-fetoprotein based on CdS nanoparticles and Thionine bilayer films modified glass carbon electrode

A novel and effective electrochemical immunosensor for the rapid determination of α-1-fetoprotein (AFP), based on electrostatic interaction of CdS nanoparticles (nano-CdS) and thionine (Thi) on poly-congo red (PCR) modified glass carbon electrode (GCE), alternately was developed. The formation of the {nano-CdS/Thi+}2 bilayer films showed a good electrochemical activity, and a couple of stable and well-defined Thi redox peaks were obtained in pH 7.0 phosphate buffer solution (PBS). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were adopted to confirm the successful stepwise layer-by-layer (LBL) assembly procedure of the immunosensor. Horseradish peroxidase (HRP) was employed to block sites against non-specific binding instead of bovine serum albumin (BSA) and amplify the response currents. Tests showed that the reduction current of the immunosensor was proportional to AFP concentration in the range of 0.30–250.00 ng/mL with a detection limit of 0.12 ng/mL. Moreover, the prepared immunosensor exhibited high sensitivity and good stability, would be valuable for clinical immunoassay of AFP.