Label-free photoelectrochemical immunoassay for α-fetoprotein detection based on TiO2/CdS hybrid

A novel photoelectrochemical immunosensor based on TiO2/CdS hybrid modified electrode was developed. The TiO2/CdS hybrid modified electrode was obtained by alternately dipping the TiO2 modified indium–tin oxide (ITO) electrode into the [Cd(NH3)4]2+ and S2− solution repeatedly. Compared with the routine method using Cd2+ solution for CdS deposition, the as obtained TiO2/CdS electrode showed enhanced photocurrent intensity with fewer coating times. After the ITO/TiO2/CdS electrode was coated with chitosan (CS), α-fetoprotein (AFP) antibodies were covalently conjugated on the surface of the electrode. Thus, a label-free photoelectrochemical immunosensor for the detection of AFP was developed by monitoring the changes in the photocurrent signals of the electrode resulting from the immunoreaction. The immunosensor displayed a linear response to AFP in the ranges from 50 pg/mL to 50 ng/mL with a relatively low detection limit of 40 pg/ml. The photoelectrochemical results for the detection of AFP in five human sera showed acceptable accuracy. The method is simple, sensitive and specific. Moreover, the studied immunosensor possessed acceptable reproducibility and storage stability. The proposed methodology was potentially attractive for clinical immunoassay.