PB@PDA nanocomposites as nanolabels and signal reporters for separate-type cathodic photoelectrochemical immunosensors in the detection of carcinoembryonic antigens.

Photoelectrochemical (PEC) immunoassays exhibiting high sensitivity and decent operability have considerable potential in areas such as cancer diagnostics. In particular, cathodic PEC configurations can prevent interference from reductive substances, which can occur in biological samples; however, challenges remain in terms of sensitivity and operability. In this study, separate-type PEC immunoassays were developed for carcinoembryonic antigen (CEA) by combining microplate-based immune recognition and off-on cathodic PEC detection. Polydopamine (PDA)-coated Prussian blue (PB) nanoparticles (PB@PDA NPs) were used as signal tags to label the detection antibody. The PB NPs and PDA captured on the microplates both disassembled under strongly alkaline conditions to generate redox-active electron acceptors. The disassembled products were quantitatively transferred to PEC detection cells and synergistically enhanced the PEC current with microstructured BiOI, which operated as a cathodic semiconductor electrode. As proof of principle, carcinoembryonic antigen (CEA) was applied to elucidate the potential application of PEC immunoassay in clinical diagnosis, and the obtained linear range of the sensor was 0.001-100 ng mL with the detection limit of 54.9 fg mL (S/N = 3). The proposed separate-type off-on PEC strategy showed high sensitivity and decent operability for CEA detection, indicating its potential for the identification of other tumor markers.