Self-Assembled Perylene Diimide (PDI) Nanowire Sensitized In₂O₃@MgIn₂S₄ S‑Scheme Heterojunction as Photoelectrochemical Biosensing Platform for the Detection of CA15–3

Inorganic/organic heterojunctions show promising applications as high-performance sensing platforms for photoelectrochemical (PEC) immunosensors. This work reports constructing a PEC biosensor for CA15–3 based on a self-assembled perylene diimide (PDI) nanowire sensitized In₂O₃@MgIn₂S₄ S-scheme heterojunction platform. P-type semiconductor Cu₂O nanoparticles were designed as a signal burst source and were used as immunoassay labels. The carboxyl group on self-assembled PDI nanowires eliminates the step of additional surface functionalization for covalent immobilization of the capture elements. The π–π stacking of PDI enhances electron generation efficiency, while the carboxylic acid groups on PDI promote electron transfer. The performance of the constructed sensor was validated using CA15–3 as a model. The experimental results showed that the sensor based on In₂O₃@MgIn₂S₄/PDI has excellent selectivity, stability, and reproducibility, and can sensitively detect CA15–3 in the range of 0.001–100 U·mL^–1 with the detection limit of 0.00056 U·mL^–1. The sensor has a broad application prospect. It is hoped that this research work based on the unique advantages of the organic compound PDI will inspire other researchers to design light-responsive materials and promote the development of the field of photoelectrochemical sensing.