Photoelectrochemical Immunosensor for Detection of Carcinoembryonic Antigen Based on 2D TiO(2) Nanosheets and Carboxylated Graphitic Carbon Nitride

Carcinoembryonic antigen (CEA) was used as the model, an ultrasensitive label-free photoelectrochemical immunosensor was developed using 2D TiO(2) nanosheets and carboxylated graphitic carbon nitride (g-C(3)N(4)) as photoactive materials and ascorbic acid as an efficient electron donor. 2D TiO(2) nanosheets was sythsized by surfactant self-assembly method and proved to have higher photoelectrochemical signals than TiO(2) nanoparticles. Firstly, carboxylated g-C(3)N(4) could be attached to 2D TiO(2) nanosheets through the bond formed between carboxyl group of carboxylated g-C(3)N(4) and TiO(2). And the photocurrent of g-C(3)N(4)/TiO(2) drastically enhances compared to carboxylated g-C(3)N(4) and TiO(2). Then, antibody of CEA was bonded to TiO(2) through the dentate bond formed between carboxyl group of anti-CEA and TiO(2), leading to the decrease of the photocurrents. As proven by PEC experiments and electrochemical impedance spectroscopy (EIS) analysis, the fabrication process of the immunosensor is successful. Under the optimal conditions, the intensity decreased linearly with CEA concentration in the range of 0.01~10 ng/mL. The detection limit is 2.1 pg/mL. The work provides an effective method for the detection of tumor markers and can be extended for the application in food safety and environmental monitoring analysis.