A ratiometric fluorescence sensor based on enzyme-regulated UiO-66-NH₂@MnO₂ for the visual detection of dichlorvos

Dichlorvos (DDVP) misuse in agriculture threatens food safety, making its monitoring crucial. Herein, a ratiometric fluorescent sensor was developed using a UiO-66-NH₂@MnO₂ composite for visual DDVP detection. The MnO₂ nanosheets (MnO₂ NSs) quenched the blue fluorescence (430 nm) of metal-organic frameworks (MOFs) UiO-66-NH₂ but oxidized o-phenylenediamine to yield yellow-emitting 2,3-diaminophenazine (DAP) at 565 nm. Acetylcholinesterase (AChE) catalyzed the generation of thiocholine, which decomposed MnO₂ NSs and restored the blue fluorescence. In contrast, the presence of DDVP inhibited AChE activity, thereby preserving MnO₂ NSs and maintaining the yellow fluorescence. A ratiometric fluorescence method and a smartphone-assisted fluorescence visualization method for DDVP were developed based on the sensor, achieving detection limits of 0.169 ng/mL and 0.756 ng/mL, respectively. Both methods successfully detected DDVP residues in tea and honeysuckle, showing satisfactory recovery and consistency with UPLC-MS/MS results. Overall, this study offers promising prospects for the routine monitoring of DDVP residues in food safety.