Dual-ligand europium-based metal–organic frameworks and hydrogels for sensitive ratiometric fluorescent detection of tetracyclines in food

Abstract

Tetracycline (TC) residues in animal-derived foods pose potential risks to human health; thus, the establishment of detection methods with high accuracy, strong sensitivity, and easy operation is of considerable importance. Within the present work, a dual-emission fluorescent probe derived from a dual-ligand europium-based MOF (NH₂-BDC-Eu-DPA) was developed and thereafter integrated into a fluorescent hydrogel to enable the rapid detection of TCs in animal-derived foods. The probe uses Eu³⁺ as the metal node, with 2-aminoterephthalic acid (BDC-NH₂) and pyridine-2,6-dicarboxylic acid (DPA) as dual ligands. Upon excitation at 260 nm, it exhibits dual fluorescence peaks at 427 nm and 617 nm. TCs can specifically quench the fluorescence at these two wavelengths through the IFE, and the quenching effect at 427 nm is more significant. Quantitative analysis is achieved based on the fluorescence intensity ratio (F₄₂₇/F₆₁₇). After optimizing the experimental conditions, this method exhibits a linear detection range of 1–200 µmol L⁻¹ for doxycycline hydrochloride (DOX), tetracycline (TC), and oxytetracycline (OTC), with a limit of detection of 31.0 nmol L⁻¹, 29.7 nmol L⁻¹, 35.1 nmol L⁻¹, respectively. In actual sample detection, the spiked recoveries for milk and pork are 91.0–106.8% and 89.7–106.4%, respectively, with a relative standard deviation (RSD) ≤ 6.5%. Furthermore, as the concentration of TCs increases, the intensity of the purple fluorescence emitted by the hydrogel shows a gradual downward trend, showing a good linear relationship. The method possesses high selectivity, anti-interference capability, and rapid response characteristics, providing reliable technical support for on-site monitoring of TC residues in animal-derived foods.