A dual-emission ln-MOF as ratiometric fluorescence sensor for detecting NF and OTC with high sensitivity and selectivity.

The abuse of antibiotics has triggered the rise of drug-resistance bacteria, which has seriously threatened public health globally. Herein, a novel lanthanide metal-organic framework (Ln-MOF) fluorescence sensor, [Eu(atpa)(hz)1/2(H2O)]n (1), (H3atpa = 4-(1H-tetrazol-5-yl)phthalic hydrazide, hz = hydrazine) was solvothermally synthesized via an in situ acylation reaction between H₃tpa and hydrazine hydrate in the presence of Eu(III). Single-crystal X-ray diffraction analysis reveals that 1 displays a 3D coordination network structure, where the Eu(III) centers and hz ligands interconnect to form a pentagonal bipyramidal geometry. Remarkably, 1 functions as a stable dual-emission ratiometric fluorescence sensor under ambient conditions (room temperature, pH = 5) and demonstrates exceptional selectivity and sensitivity toward Nitrofurazone (NF) and Oxytetracycline (OTC), with low limit of detection (LOD = 61.72 nM for NF and LOD = 57.76 nM for OTC). Mechanistic studies combining UV-Vis and XPS analyses revealed that the fluorescence quenching of 1 at 650 nm arises from the synergistic effects of the inner filter effect (IFE) and 1-analyte interactions. Density functional theory (DFT) calculations further confirmed the absence of photoinduced electron transfer (PET). Additionally, fluorescence lifetime measurements ruled out Förster resonance energy transfer (FRET) and PET as possible quenching mechanisms.