A colorimetric and ratiometric fluorescent paper chip for biogenic amine monitoring based on a simple pH-sensitive AIEgen

Existing single-signal-response fluorescent materials for biogenic amine detection have unsatisfactory detection performance. Herein, we developed a simple pH-sensitive aggregation-induced emission-active fluorogen (AIEgen) and demonstrated its potential for ratiometric monitoring of biogenic amines. This AIEgen, namely 4-(dimethylamino)styryl)quinoxalin-2(1H)-one (ASQ), shows a typical donor (D)-acceptor (A) structure with nonmonotonic color and fluorescence responses to pH stimulation by its protonation/deprotonation on the D/A moieties. Subsequently, the H⁺ASQ-labeled paper chips were successfully prepared by physically depositing ASQ on qualitative filter paper, followed by the acidification by hydrochloric acid. Upon the exposure to ammonia vapour, the obtained H⁺ASQ-labeled paper chips exhibited obvious color and ratiometric fluorescence responses owing to the deprotonation of H⁺ASQ indicators, indicating that the proposed paper chips can be used for the detection of biological amines by bimodal colorimetry and ratiometric fluorescence. Under the optimal conditions, H⁺ASQ-labeled paper chip achieved the real-time, non-destructive, and visual monitoring of meat and seafood freshness by simultaneously quantify the biogenic amine index with high performance liquid chromatography (HPLC). The results of this work suggest that ratiometric AIEgen can serve as a promising alternative strategy to ensure accurate monitoring of biogenic amines and food freshness.