Design of terbium (III)-functionalized covalent organic framework as a selective and sensitive turn-on fluorescent switch for ochratoxin A monitoring

Abstract For the first time, we develop a terbium (III)-functionalized covalent organic framework named Dpy-NhBt-COF@Tb3+, through anchoring Tb3+ onto a two-dimensional imine COF (Dpy-NhBt-COF), as the selective and sensitive turn-on fluorescent switch for ochratoxin A (OTA) monitoring. Of particular significance, Tb3+ actually plays two roles during sensing process: the specific response signal, and exclusive recognition sites for OTA, while Dpy-NhBt-COF acts as the protector for Tb3+. The sensing process involves the replacement of coordinated water molecules from Tb3+ by OTA and the energy transfer from OTA to Tb3+ centers, resulting in remarkable fluorescence emergence of Tb3+. The stabilization of Tb3+ via coordination with bipyridine of Dpy-NhBt-COF not only reduces the nonselective binding of naturally occurring ligands, but also avoids the non-radiative quenching caused by solvents molecules. As a sensing platform, Dpy-NhBt-COF@Tb3+ possesses noticeable selectivity and high sensitivity toward OTA with an ultralow detection limit of 13.5 nM and rapid response of 10 s. Taken together, our work not only demonstrates great prospect of Tb3+-functionalized COF for OTA detection, but also provides a potential way to explore other functionalized materials as promising sensors for other targets.