In2O3/CdIn2S4 heterojunction-based photoelectrochemical immunoassay of carcinoembryonic antigen with enzymatic biocatalytic precipitation for signal amplification

This work reported a split-type photoelectrochemical (PEC) immunoassay for the detection of carcinoembryonic antigen (CEA) based on target-induced biocatalytic precipitation (BCP) by using In2O3/CdIn2S4 heterojunctions as the photosensitizers. The synthesized In2O3/CdIn2S4 heterojunctions improved the efficiency of charge separation and shortened the electron convey path to enhance the photocurrent, thus exhibiting high conductivity and low complexation rates of photogenerated electrons and holes. In the presence of CEA, horseradish peroxidase (HRP) catalyzed 4-chloro-1-naphthol (4-CN) to produce benzo-4-chloro-hexadienone (4-CD) through H2O2. Then, 4-CD was deposited onto the surface of In2O3/CdIn2S4 to reduce the photocurrent and realized the signal amplification. The PEC immunoassay revealed an excellent photocurrent toward target CEA within a wide range of 0.01-50 ng mL-1 at a low limit of detection of 2.8 pg mL-1 under the optimum conditions. Multiple switching light excitation tests demonstrated the good reliability and stability of the fabricated PEC biosensor. The accuracy was acceptable in comparison with human CEA enzyme-linked immunosorbent assay (ELISA) kit.