A D-π-a type fluorescent probe with dual-responsive viscosity and TMA for point-of-care food freshness evaluation

Real-time monitoring of changes in chemical markers and the physical microenvironment is crucial for a comprehensive assessment of food safety. Here, we have rationally designed a novel push-pull electronic (D-π-A) structure fluorescent probe SK, which has orthogonal dual-response capabilities for viscosity and trimethylamine (TMA). Thanks to the intramolecular rotation-restricted (RIR) effect, SK exhibits a significant fluorescence brightening response at 590 nm in response to increased viscosity. TMA can specifically attack the alkenyl bridge of SK, irreversibly blocking the intramolecular charge transfer (ICT) process, which leads to a significant blue shift in the emission ratio from 590 nm to 480 nm. Thanks to this sensing mechanism, SK has been successfully prepared into intelligent test strips for in situ, visual tracking of the dynamic spoilage process of fresh meat and shrimp. Additionally, by combining the probe with a color recognition platform based on smartphones, we have established a portable, real-time testing strategy for rapid, semi-quantitative analysis of natural spoilage extracts. This work not only provides multi-dimensional molecular tools for biosensing, but also presents a highly practical example for intelligent food packaging and on-site quality control.