A pH-responsive dual-emission composite for fast detection of BAs and visual monitoring seafood freshness with large luminescence color difference.

Sensing biogenic amine (BAs) content is very important for assessing food freshness. To address the limitations such as small color difference values (ΔE) and complex preparation of probes for visualizing the freshness of seafood, a pH-responsive ratiometric fluorescent probe (EnEB) was prepared by Eu(NO), trimeric acid (BTC), and hydrochloric acid norepinephrine (Enr). EnEB emitted blue (446 nm) and red fluorescence (616 nm) originating from Enr and Eu, respectively, and exhibiting a fluorescence wavelength difference up to 170 nm. The ratiometric fluorescent signals of EnEB showed a linear correlation with pH in the range of 5.5-8.0. Thus, EnEB can rapidly and precisely detect BAs, such as histamine, tyramine, and spermine, with detection limits and response times of 1.14 μmol/L (3 s), 1.04 μmol/L (8 s), and 0.41 μmol/L (2 s), respectively. Furthermore, an EnEB aerogel was prepared by loading EnEB in a matrix formed by polyvinyl alcohol (PVA) and agarose (AG). EnEB aerogel exhibited excellent acid-base gas-sensing properties. The fluorescence color of EnEB aerogel can change significantly with the deterioration of seafood. When seafood changed from fresh to decayed, the ΔE value of EnEB aerogel was as high as 80.9. Importantly, the results of seafood freshness by naked eye using EnEB aerogel was consistent well with the TVB-N content and the freshness standard stipulated by national food standard, indicating EnEB aerogel can accurately visually and real-time monitor seafood freshness. Furthermore, the strategy for sensing food freshness based on EnEB aerogel also offered multiple color variations to indicate fine freshness levels of seafood. This work provided a convenient, efficient, and accurate approach to assessing the freshness of seafood. Additionally, EnEB also has promising applications in security and anti-counterfeiting.