A quinolinium-based colorimetric and NIR fluorescent dual-channel sensing platform for specific detection of bisulfite in food, traditional Chinese medicine and living cells

Sulfur dioxide (SO₂) and its derivatives are commonly used in food processing, but excessive exposure to SO₂ and its derivatives can pose serious health risks. In this study, we present a near-infrared “turn-on” probe, QSB-M, for the highly selective and sensitive detection of HSO₃⁻. The recognition of HSO₃⁻ by the probe results in a marked color change and a significant enhancement in near-infrared fluorescence, offering high sensitivity (limit of detection = 95.12 nM), rapid response, and minimal interference from environmental background signals. The recognition mechanism involves the specific addition of HSO₃⁻ to the 4-position of the quinolinium moiety, triggering an intramolecular charge transfer effect that leads to both colorimetric and fluorescence dual responses. QSB-M was also successfully applied for in situ visualization of HSO₃⁻ in various foods and traditional Chinese medicines (TCM), with recoveries ranging from 90 % to 115 %. Additionally, test strips and a smartphone-assisted sensing platform were developed, enabling direct detection of HSO₃⁻ levels in foods and TCM without the need for complex instrumentation. Importantly, QSB-M exhibits low cytotoxicity, good mitochondrial-targeting ability, and has been successfully used for the in situ detection of both endogenous and exogenous HSO₃⁻ in live MCF-7 cells.