Cysteine-assisted photoelectrochemical immunoassay for the carcinoembryonic antigen by using an ITO electrode modified with C3N4-BiOCl semiconductor and CuO nanoparticles as antibody labels

A sensitive photoelectrochemical (PEC) immunoassay for the carcinoembryonic antigen (CEA) is described that is based on the use of C 3 N 4 -BiOCl semiconductor on an ITO electrode. The photocurrent of the modified electrode was measured under visible light illumination. It increased in presence of L-cysteine due to rapid separation of the photoexcited electrons and holes. A sandwich-type immunoassay in a 96-well microtiter plate format used CuO nanoparticles as label for the secondary antibody. The Cu 2+ is released from the CuO in the sandwich complex by treatment with acid. The free Cu 2+ combined with both the cysteine and the electron receptors of C 3 N 4 and BiOCl. Under optimal conditions, this dual action immensely decreases the photocurrent of the PEC system, and the response is inversely proportional to the CEA concentrations from 0.1 pg mL −1 to 10 ng mL −1 at the working voltage of 0 V (vs. SCE). The detection limit is 0.1 pg mL −1 , and the method is exhibited satisfactory selective, repeatable and stable. Schematic representation of an immunoassay based on cysteine-assisted C 3 N 4 -BiOCl photoelectrochemical platform. CuO nanoparticles were utilized as labels in immunocomplex to release Cu 2+ in acidic condition. Carcinoembryonic antigen in sample was detected sensitively by dual function of Cu 2+ with cysteine and C 3 N 4 -BiOCl semiconductor.