Cascade Catalytic Iron Phosphate Nanozyme-Driven Signal Amplification in S-Scheme AgBr/La-BiOBr-OV for Sensitive Dual-Channel Microfluidic PEC Detection of CA15-3 and CA125

An innovative dual-channel microfluidic photoelectrochemical (PEC) immunosensor was constructed for simultaneous determination of carbohydrate antigen 15-3 (CA15-3) and cancer antigen 125 (CA125). Herein, AgBr-sensitized La-doped BiOBr with surface oxygen vacancies (AgBr/La-BiOBr-OV) was synthesized as a photoactive material to provide a stable photocurrent. Constructing an S-scheme heterojunction with AgBr and BiOBr facilitates the effective separation of photogenerated carriers. Meanwhile, the introduction of La and oxygen vacancies extends the range of visible-light absorption and improves the light utilization. To strengthen the PEC performance, a cascade catalytic amplification strategy was introduced using iron-phosphate-based (FePOs) nanozymes. These nanozymes exhibit dual enzyme-mimicking activities, including catalase (CAT)-like and superoxide dismutase (SOD)-like functions, enabling the sequential disproportionation of •O₂^- into H₂O₂ and O₂, followed by the decomposition of H₂O₂ into O₂ and H₂O. The generated oxygen acts as an efficient electron acceptor, promoting the removal of photogenerated electrons and consequently boosting the PEC response. Under optimized conditions, the developed immunosensor enables highly sensitive quantification of CA15-3 (0.0005-200 U/mL) and CA125 (0.001-200 U/mL), with corresponding limits of detection (LOD) of 0.00016 and 0.0003 U/mL, respectively. This study provides a promising approach to constructing efficient S-scheme photoactive heterostructures and offers new insights into nanozyme-based cascade amplification for high-performance PEC biosensing.