A “Signal Relay” Mode Triggered by Bimetallic Synergistic Enhancement in an MOF-Based Multiemission Fluorescence Sensing/Adsorption Platform for Broad-Concentration-Range Tetracycline Antibiotics Visual Detection

The widespread misuse of tetracycline antibiotics (TCs) and their persistent low-concentration residues in animal-derived foods pose critical threats to human health, while existing analytical methods lack the capability for continuous therapeutic drug monitoring. Herein, a multiemission MOF-on-MOF fluorescence sensing platform codoped with Eu3+ and Zn2+ was engineered via epitaxial growth for simultaneous adsorption and detection of tetracycline, oxytetracycline, chlortetracycline, and doxycycline. By leveraging the differential coordination affinities of Eu3+ and Zn2+ toward TCs, a “signal relay” response mechanism was innovatively designed: At trace concentrations (0.05–6 μM), TCs preferentially bind to Eu3+ sites via the antenna effect, generating linearly enhanced fluorescence at 616 nm with an ultralow detection limit of 9 nM (22-fold below EU MRLs). Upon Eu3+ site saturation (>6 μM), Zn2+ domains initiate coordination-induced aggregation of TCs, triggering a second-stage fluorescence enhancement at 520 nm that extends the dynamic range to 40 μM. This platform was successfully applied to detect TCs across wide concentration ranges in environmental water, animal-derived foods, and veterinary drugs. A novel dual-metal-doped MOF-on-MOF integrates broad detection range, fast adsorption kinetics, better stability, and multiscenario applicability, while multiemission wavelengths enhance the sensitivity of fluorescence color changes, better meeting practical needs for visual detection.