An ultrasensitive and visual ratio fluorescence sensing platform for tannic acid in water based on boric acid functionalized lanthanide MOF

Tannic acid (TA) is a natural polyphenol that is widely used as a preservative and antioxidant in foods, beverages, health products and pharmaceuticals. In this study, a novel Eu-MOF skeleton was prepared using a simple solvothermal strategy and used as a ratio-metric fluorescence sensor for the ultra-sensitive detection of TA. The constructed Eu-MOF has excellent fluorescence properties and high stability in the aqueous phase. With the introduction of TA, a special covalent structure is formed between the o-diphenol group of TA and the boric acid hydroxyl group in ligand of the MOF, resulting in a gradual decrease in the red emission of Eu-MOF at 614 nm and a basically invariable blue emission at 420 nm. As the concentration of TA increased, the color of the system also changes from red to blue, thus achieving rapid and sensitive detection with a low limit of detection (LOD) of 75.6 nM through a ratiometric fluorescence strategy. What is more, Eu-MOF fluorescent probe combined with smart phone color detector is used to visually detect TA. The propose method is successfully applied in the target analysis in tea and beverage samples and the recovery is 95.6∼110.0 %, which is proved to be an effective strategy for the food safety and healthy monitoring.