Pyrazinoquinazoline-Based Eu-MOF Ratiometric Fluorescence Sensing: Real-Time Monitoring of Meat Spoilage Enabled by Dynamic Regulation of LMCT/LLCT Triggered by Biogenic Amines.

This study develops a dual-emission Eu-MOF ratiometric fluorescence sensor for biogenic amine detection in food spoilage monitoring. The sensor exhibits dual emission at 495 nm (ligand π→π* transition) and 615 nm (ligand-to-metal charge transfer, LMCT) through the antenna effect. Biogenic amines specifically regulate the intensity ratio (I/I) by adsorbing into MOF pores via hydrogen bonding, triggering a dynamic equilibrium switch between LMCT and ligand-to-ligand charge transfer (LLCT), causing fluorescence color shift from orange to green. Theoretical calculations reveal this response mechanism for the first time. Encapsulating Eu-MOF in agarose hydrogel-based portable tags with smartphone RGB analysis enables rapid quantitative detection of biogenic amines (detection limit: 3.7-9.1 µM, response time <10 min). The sensor allows real-time tracking of spoilage in shrimp and chicken stored at 0-25 °C, with visual fluorescence color transitions reflecting amine accumulation levels. This work provides molecular insights into dynamic charge transfer regulation and establishes a high-sensitivity, visual, wearable solution for on-site food safety detection, advancing smart sensing technology in the food industry.