Multi-emitter metal-organic frameworks as ratiometric luminescent sensors for food contamination and spoilage detection.

Food contamination and spoilage is a worldwide concern considering its adverse effect on public health and food security. Real time monitoring food quality can reduce the risk of foodborne disease to consumers. Particularly, the emergence of multi-emitter luminescent metal-organic frameworks (LMOFs) as ratiometric sensory materials has provided the possibility for food quality and safety detection with high sensitivity and selectivity taking advantage of specific host-guest interactions, pre-concentrating and molecule-sieving effects of MOFs. Furthermore, the excellent sensing performance of multi-emitter MOF-based ratiometric sensors including self-calibration, multi-dimensional recognition and visual signal readout is able to meet the increasing rigor requirement of food safety evaluation. Multi-emitter MOF-based ratiometric sensors have become the focus of food safety detection. This review focuses on design strategies for different multiple emission sources assembly to construct multi-emitter MOFs materials based on at least two emitting centers. The design strategies for creating multi-emitter MOFs can be mainly classified into three categories: (1) multiple emission building blocks assembly in a single MOF phase; (2) single non-luminescent MOF or LMOF phase as a matrix for chromophore guest(s); (3) heterostructured hybrids of LMOF with other luminescent materials. In addition, the sensing signal output modes of multi-emitter MOF-based ratiometric sensors have critically discussed. Next, we highlight the recent progress for the development of multi-emitter MOF as ratiometric sensors in food contamination and spoilage detection. Their future improvement and advancing direction potential for their practical application is finally discussed.