Photoelectrochemical immunoassay for the breast cancer biomarker CA 15-3 based on In2O3/ZnIn2S4 heterojunctions

The development of sensitive breast cancer biomarker (CA 15-3) measurement techniques is of great significance for the early diagnosis and therapeutic monitoring of breast cancer worldwide. Herein, we have designed a split-type photoelectrochemical (PEC) immunoassay platform for the ultrasensitive determination of CA 15-3 using In2O3/ZnIn2S4 heterojunctions with high photovoltaic conversion performance as a photoactive substrate. Efficient photocurrent-responsive In2O3/ZnIn2S4 was formed by surface loading narrow-bandgap ZnIn2S4 on MOF-derived wide bandgap In2O3 nanomaterials. Subsequently, a sandwich immunoreaction was performed using an alkaline phosphatase (ALP)-labeled secondary antibody as a signaling indicator to produce large amounts of ascorbic acid by enzymatic biocatalysis. Since ascorbic acid is an excellent electron donor capable of promoting photogenerated electron separation in semiconductor materials, it enhances the anodic photocurrent of In2O3/ZnIn2S4-modified electrodes. Under the optimal catalyst loading and immunoreaction time, the In2O3/ZnIn2S4-based PEC immunoassay showed a good photocurrent response to CA 15-3 over a wide detection range from 1.0 mU mL−1 to 10 000 mU mL−1 with a limit of detection of 0.45 mU mL−1. Owing to the excellent photocurrent response of In2O3/ZnIn2S4 to ascorbic acid and the split-type immunoassay protocol, the constructed PEC immunosensing platform has the advantages of high precision, anti-interference, and acceptable accuracy, and the results are equivalent to those of commercial enzyme-linked immunosorbent assay (ELISA) kits.