Sensitive and visual colorimetric detection of AFB1 based on MOF-on-MOF bimetallic nanozymes

Aflatoxin B1 (AFB1) is widely present in food crops and their products, posing significant risks to human health as a contaminant. Therefore, developing reliable, rapid, and convenient detection methods for AFB1 is crucial to ensure food safety. In this study, a MOF-on-MOF strategy was employed to prepare bimetallic MOF, using MIL-101 (Fe) as the host metal-organic framework (MOF) and MIL-125 (Ti), which exhibits excellent peroxidase-like activity and photosensitivity, as the guest. The material was then calcined under a nitrogen atmosphere to promote the carbonization of the framework and the development of a hollow structure, resulting in the fabrication of MIL-125@MIL-101-N₂ catalyst. This method utilizes the distinct properties of iron and titanium to lower the reaction barriers in the colorimetric process. The host-guest interaction in the MOF-on-MOF structure prevents the excessive coordination of Fe, which would speed up the recombination of photogenerated electron-hole pairs, thereby broadening the light absorption range and boosting the photogenerated electron capability. Based on the bimetallic MOF-on-MOF strategy, a colorimetric sensor was constructed with MIL-125@MIL-101-N₂ material and aptamer as recognition element for detection of AFB1. The results demonstrated a linear relationship between the RGB values and AFB1 concentrations in the range of 1-1380 ng/mL, which can be used for sensitive and visual detection of AFB1.