Ratiometric fluorescent sensor based on europium (III)-functionalized covalent organic framework for selective and sensitive detection of tetracycline

Tetracycline (TC), a typical food contaminates, is of serious harmful impact toward human health. To explore simple methods for effective monitoring of TC-stained foods has extraordinary significance. Herein, we explored for the first time an europium (III)-functionalized fluorescent covalent organic framework (Dpy-TFPB-COF@Eu3+) via fixing Eu3+ onto a bipyridine-containing COF (Dpy-TFPB-COF) for ratiometric detection of TC in outstanding selectivity and sensitivity. In this sensor, Eu3+ performs as the recognition sites and specific response signal for TC, while Dpy-TFPB-COF is the fluorescent reference and shelter for Eu3+. Once TC is present, TC displaced water molecules to coordinate on Eu3+, and thereby generating remarkable fluorescence signal of Eu3+ based on sensitization mechanism, while the original fluorescence of Dpy-TFPB-COF remained. Profiting from its high porosity, the interaction between Dpy-TFPB-COF@Eu3+ and TC attained equilibrium only within 10 s. The detection limit of TC is achieved as ultralow as 7.5 nM. Based on these, lanthanide-based fluorescent COF was demonstrated as a ratiometric sensor toward TC with excellent selectivity and sensitivity, rapid response, self-calibration, and non-interference. This work not only exhibits fascinating performance of Eu3+-functionalized fluorescent COF toward the ratiometric sensing of TC, but also offers a prospective manner to explore various specific materials for multiple aims.