CdS quantum dots sensitized Ti-MOFs as high-performance photocathodic materials for immunoassay of alpha-fetoprotein based on Ag+ exchange strategy

Cathodic photoelectrochemical (PEC) analysis has drawn much attention because of its excellent anti-interference capability toward reductive substances in samples, but the development high-performance photocathodic materials is challenging. We report here CdS quantum dots (QDs) sensitized titanium-based metal–organic frameworks (Ti-MOFs) as high-performance photocathodic materials for ultrasensitive immunoassay of alpha-fetoprotein (AFP) based on Ag+ exchange strategy. Due to the excellent sensitization effect of CdS QDs, the photocathodic current of CdS QDs decorated MIL-125-NH2(Ti) is 25-fold that of MIL-125-NH2(Ti) alone. The photocathodic current of CdS/MIL-125-NH2(Ti) can be quenched after Ag+ exchange, because CdS is partially converted to Ag2S that serves as a charge-recombination center. Based on the PEC response of CdS/MIL-125-NH2(Ti) to Ag+, a cathodic PEC immunoassay platform is constructed for AFP detection by using CdS/MIL-125-NH2(Ti) as the photoactive material and Ag nanoparticles modified SiO2 nanospheres as labels. The linear range for AFP detection is from 1.0 × 10−4 to 1.0 × 102 ng mL−1, and the detection limit is 20 fg mL−1. The constructed PEC immunosensor is successfully used for detecting AFP in human serum samples. In this work, a novel and high-performance photoactive material is developed for cathodic PEC analysis, and a simple and effective PEC immunoassay platform for AFP detection is constructed based on Ag+ exchange strategy.