Ultrasensitive and selective detection of metronidazole residues in milk powder using a novel 3D MOF fluorescent sensor

The presence of metronidazole (MNZ) residues in food poses significant risks to human health. In this study, two metal–organic framework (MOF)-based fluorescent probes, [Ba(bbda)]_n (1) and [Cd(bbda)]_n (2), were developed for the rapid and ultrasensitive detection of MNZ in food samples. Upon addition of MNZ, both probes exhibited significant fluorescence quenching with favorable linear ranges and low detection limits of 37 nM and 64 nM, respectively. Fluorescence lifetime and density functional theory (DFT) calculations revealed that the quenching mechanism involves a synergistic effect of the inner filter effect (IFE), photoinduced electron transfer (PET), and specific ligand–analyte interactions. Probe 1 was successfully applied to quantify MNZ in commercial pharmaceutical tablets and milk powder, achieving excellent recoveries of 97% and 102.6%, respectively, demonstrating its reliability for trace-level MNZ detection in food matrices.