Constructing A-π-D-π-A type long wavelength emission fluorescent probe for biogenic amine detection and its application in food quality monitoring

Biogenic amines (BAs) such as cadaverine are key indicators of food spoilage, and their rapid and selective detection is crucial for food safety and quality monitoring. Herein, we report a novel fluorescence probe, TIP-BT, designed on an A-pi-D-pi-A structural motif. Unlike conventional BA sensors that rely predominantly on noncovalent interactions, TIP-BT operates via a covalent recognition pathway: the benzothiazolium moiety undergoes a nucleophilic addition reaction with cadaverine, forming a stable adduct (TIP-BT + Cad). This transformation effectively suppresses competing non-radiative decay pathways, thereby enhancing the probe's intramolecular charge transfer (ICT) process. Spectroscopic analyses revealed a distinct and pronounced "turnon" fluorescence emission centred at 633 nm, which was accompanied by a remarkable elongation in fluorescence lifetime, indicating the suppression of non-radiative decay pathways upon cadaverine binding. Comprehensive structural and mechanistic evidence for this recognition process was obtained through a combination of NMR spectroscopy, TOF-MS, SEM imaging, and TD-DFT calculations, all of which consistently supported the proposed covalent sensing mechanism. The TIP-BT probe exhibited outstanding selectivity toward cadaverine when compared with other structurally related biogenic amines, clearly demonstrating the mechanistic advantage conferred by covalent interaction. In addition, TIP-BT displayed notable solvatochromic behaviour, high molar absorptivity exceeding 105 M- 1 cm- 1, and a satisfactory fluorescence quantum yield, enabling highly sensitive and reliable detection with a low detection limit of 2.48 mu M under optimized conditions. Practical applicability was verified by detecting cadaverine in real food samples, including fish and meat extracts, showing distinct fluorescence changes under UV light. These findings demonstrate the potential of TIP-BT for rapid, visual, and instrument-free freshness monitoring and introduce a novel benzothiazolium-based reaction pathway for biogenic amine detection with excellent selectivity, stability, and practical usability.