Smart fluorescent tag based on amine response for non-contact and visual monitoring of seafood freshness

The method of monitoring the freshness of seafood is not satisfactory for ensuring food safety. Here, we develop a filter membrane-based smart fluorescent tag with excellent biogenic amine response, which can monitor the freshness of seafood in real time and visually. We use green fluorescent fluorescein as an indicator and red fluorescent carbon quantum dots (RQDs) with aggregation-induced emission property as an internal reference. After simple mixing, they are deposited on the commercial filter membrane by physical deposition method to prepare the fluorescent tag. When amine molecules are present, the molecular conformation of fluorescein changes and the fluorescence increases rapidly, while RQDs have no obvious response, thus achieving a clear fluorescence color response to biogenic amines. Under UV light of 254 nm and 365 nm, the fluorescent tag showed sensitive, rapid, and color-responsive to ammonia in a wide range of 250–2.5 × 104 ppm. To further verify the practical application potential, the fluorescent tag was used to monitor the freshness of shrimp and crab in situ in real time, and satisfactory results were achieved. More importantly, owing to the reversible conformational change of fluorescein, the fluorescent tag can be reused and manufactured at low cost, making it a more attractive platform for freshness monitoring in the field of food safety.