A lanthanide-MOF based host-guest intelligent dual-stimulus response platform for naked-eye and ratiometric fluorescence monitoring of food freshness

Developing a simple, rapid, and accurate sensing platform to detect tyramine (Tyr), an indicator of food spoilage, is tremendously significant for food safety and human health. Here, two novel isostructural lanthanide metal-organic frameworks (Ln-MOFs) [Ln(dbia)(COO)]_n (Ln-dbia, Ln = Sm, Eu, H₂dbia = 5-((4′-(imidazol-1-yl)benzyl)oxy)isophthalic acid) with high chemical stability have been successfully synthesized and employed as a host to setup a ratiometric fluorescent platform. A dual-emission Flu@Eu-dbia probe is constructed by encapsulating the guest luminescent molecule fluorescein (Flu) in Eu-dbia due to the suitable pore structure, strong host-guest interaction and rapid electron transfer, which shows significantly improved fluorescence sensitivity to Tyr (LOD: 66.3 nM) along with a clearly distinguishable color transition from red to green. Furthermore, Flu@Eu-dbia containing portable test strips are fabricated and successfully applied for monitoring the freshness of beef in practical application. More importantly, an intelligent logic gate is designed to record the ratiometric fluorescence change of Flu@Eu-dbia vs. the concentration level of Tyr, which exhibited a great promise in the application of smart devices for food safety.