Split-type photoelectrochemical immunosensor integrating ZIF-8@Ag NPs-assisted cation-exchange and Fe2O3/ZnIn2S4 nanoarrays for detection of carbohydrate antigen 72–4

The sensitivity, accuracy, and stability of a photoelectrochemical (PEC) immunosensor directly depends on the type of sensing substrate and the efficiency of the recognition model in immobilizing biological elements within multilayer assemblies. In this work, a split-type PEC immunosensor integrating Ag nanoparticles-modified ZIF-8 (ZIF-8@Ag NPs)-assisted cation-exchange and Fe₂O₃/ZnIn₂S₄ nanoarrays (NAs) as well-ordered sensing substrate and photoactive material was developed for the detection of carbohydrate antigen 72–4 (CA72–4), a novel gastric cancer target. With effectively harvesting visible light, the stability signal output and the rapid carrier separation, the Z-Scheme Fe₂O₃/ZnIn₂S₄ NAs heterojunction was successfully grown on an indium tin oxide (ITO) electrode as the signal converter and sensing substrate via two-step solvothermal method. The ZIF-8@Ag NPs were employed as the signal label to release silver ions (Ag⁺), relying on the acidolysis in the 96-well plate. The released Ag⁺ initiated a cation-exchange (CE) reaction with the Fe₂O₃/ZnIn₂S₄ NAs, forming Fe₂O₃/ZnIn₂S₄/Ag₂S ternary complexes with higher photocurrent density. This resulted in a positive correlation trend between CA72–4 concentration (0.01 U/mL to 100 U/mL), and improved the recognition sensitivity of the sensor to trace target, with the limit of detection is 0.0032 U/mL. This work represents an important advancement in overcoming the limitations of multilayer assembly in constructing immunosensors, providing a valuable reference for trace detection of low-abundance disease-related biomarkers.