Self-Powered PEC Cathodic Immunosensor for CA125 Detection Based on the Cu₂O Photocathode and the CdS/PANI Photoanode

The photoelectrochemical (PEC) biosensors relying on anodic photocurrent modulation are prone to producing false-positive results due to the interference from reductive species in samples, while the PEC sensors based on cathodic response often exhibit insufficient sensitivity in practical applications. To address this issue, herein we synthesized CdS via a hydrothermal method and encapsulated it with polyaniline (PANI) to create a high-performance CdS/PANI heterojunction photosensitive material. Then, the composite was used as a photoanode, paired with the Cu₂O photocathode, establishing a self-powered system, wherein the CdS/PANI photoanode supplied photogenerated electrons to the Cu₂O photocathode. Owing to the strong driving force provided by the Fermi-level difference between CdS/PANI and Cu₂O for electron migration, the dual-photoelectrode system produced a strong and stable cathodic response signal, which was up to 23 times that of a three-electrode system, laying the foundation for constructing a highly sensitive sensor. On this basis, the Cu₂O electrode functioning as a working electrode was modified by electrodeposited gold nanoparticles (Au NPs), followed by the immobilization of recognition element CA125 antibody through Au-N bonds, targeting the model molecule carbohydrate antigen CA125. Consequently, the obtained self-powered dual-photoelectrode immunosensor demonstrated exceptional analytical performance, including a wide quantitative detection range of 0.001-100 ng mL^-1, a low detection limit of 0.26 pg mL^-1, high stability, reproducibility, anti-interference capability, and practicability. Furthermore, this sensing platform is readily adaptable to monitoring other disease biomarkers.