Dual-Ligand Terbium Metal–Organic Framework for Visual Ratiometric Fluorescence Sensing of Nitrites in Pickles

Nitrites are food additives, and they can also be produced as a byproduct during the fermentation procedure. Developing a simple and sensitive nitrite content assay method is critical for human health. Here, we have proposed a ratiometric fluorescence strategy for the detection of nitrites (NO2–) using a dual-emission terbium-metal–organic framework (Tb-MOF). The MOF was synthesized with Tb3+ and mixed ligands. 5-Boronoisophthalic acid sensitized Tb3+ via the antenna effect and BDC-OH (2-hydroxyterephthalic acid) exhibited a bright blue emission. The response of BDC-OH and Tb3+ ions to NO2– was enhancement of the emission at 429 nm and quenching of the emission at 550 nm. This is the first MOF-based fluorescent platform for ratiometric sensing of NO2– in food, and the NO2– content trends during the pickling process were verified. While the incidents of food poisoning could be effectively prevented, guidance for processing pickles with high safety was also developed in terms of NO2– which is of great significance to public health.