Smartphone-assisted ratiometric fluorescence sensing platform using Eu/DUT-52 hydrogel for on-site detection of aflatoxin B1.

A dual-emission, ratiometric fluorescence sensor is reported based on a europium(III)-doped metal-organic framework (Eu/DUT-52) that exhibits blue emission from DUT-52 and red emission from Eu³⁺. Notably, we fond that aflatoxin B1 (AFB1) enhances the fluorescence intensity of DUT-52, whereas the Eu³⁺ emission remains essentially unchanged, enabling ratiometric detection with a concentration-dependent color change from pink to purple. We further investigated the origin of this fluorescence enhancement. The ratiometric response provides a detection limit of 3.9 ng mL⁻¹. For field deployment, Eu/DUT-52 was embedded in a hydrogel to form a simple assay kit, and AFB1 was quantified by smartphone-based RGB analysis of fluorescence images, enabling instrument-free readout with a detection limit of 0.04 µg mL⁻¹. The hydrogel sensor shows good selectivity against other mycotoxins and common metal ions with recoveries of 80.59-111.7% in real samples. This work provides a low-cost, recognition-element-free platform for rapid, on-site screening of AFB1.