Machine Learning–Assisted Fluorescent Eu@ZnMOF for the Enoxacin and Glyphosate Detection in Food by Suppressing Sensitization and Ligand–Metal Charge Transfer

Abstract

The antibiotics and pesticides in the ecosystem environment, owing to their extensive application in veterinary medicine and insecticides, present a significant hazard to public health. Herein, we developed a novel bimetallic metal-organic framework (MOF) as a ratiometric fluorescent sensor for the simultaneous monitoring of enoxacin (ENX) and glyphosate (GLY). To fabricate a dual-responsive probe, we synthesized the ZnMOF by reacting Zn²⁺ ions with the ligands (2,2′-bipyridine-5,5′-dicarboxylic acid, 8-hydroxyquinoline, and 2-aminoterephthalic acid). Subsequently, the bimetallic Eu@ZnMOF was synthesized by loading europium (Eu³⁺) ions into the ZnMOF based on the coordination with the 2,2′-bipyridine-5,5′-dicarboxylic acid sites. The Eu@ZnMOF-based detection system exhibits a distinct green emission due to the suppression of excited-state intramolecular proton transfer in 8-hydroxyquinoline by Zn²⁺ ions. In the detection system, ENX enhances the red emission of Eu@ZnMOF by sensitizing Eu³⁺ ions. Accordingly, the ENX fluorescent sensing system was fabricated. Moreover, ENX-modified Eu@ZnMOF was fabricated. Upon the addition of GLY, suppression of sensitization and ligand-to-metal charge transfer (LMCT) occurs, which quenches the red emission of Eu³⁺ and boosts the blue emission, resulting in a distinct color transition from red to blue. The ratiometric fluorescent sensor allows detection limits of 0.05 and 0.10 mg/L for ENX and GLY, respectively. Moreover, we integrated this material into a microfluidic chip. By combining this platform with smartphone imaging and machine learning algorithms, we constructed a rapid detection protocol capable of simultaneous multi-sample analysis. These results demonstrate the promising application potential of Eu@ZnMOF for advanced environmental and food-safety testing.