Stable dual-emissive fluorescin@UiO-67 metal-organic frameworks for visual and ratiometric sensing of Al3+ and ascorbic acid.

Abstract Encapsulation of fluorophore in metal organic framework (MOF) is an effective method to construct multi-emissive composites. Unfortunately, the small molecules loaded in MOF pores are easy to leak. To overcome this difficulty, fluorescin (FL) is proposed to be encapsulated tightly in the cage of the small tetrahedron of UiO-67, as one of the organic ligands coordinated with the central ion Zr. Finally, stable multi-emission fluorescence was successfully achieved, and Forster resonance energy transfer (FRET) occurred between FL and UiO-67. Ascorbic acid (AA) can dynamically quench the fluorescence of FL@UiO-67 nanoclusters (NCs) through internal filtering effect, photoinduced electron transfer (PET). The detection limit of the probe for AA was as low as 0.20 μM, and the detection range was 0.67 μM-0.36 mM. The probe was further employed to detect Al3+ due to the coordination between Al3+ and the carboxyl group in the FL@UiO-67 NCs. The detection limit for Al3+ was 3.3 nM, and the linear range was 11 nM-5 μM agarose film and test paper were both prepared successfully for visual detection of AA and Al3+. This work provides new ideas for low-cost and convenient real-time detection method.