A chromogenic and NIR fluorescence turn-on probe for sensitive and specific visualizing SO₂ in food

Sulfur dioxide (SO₂) is extensively utilized as a food preservative, yet excessive intake poses risks to human health. To achieve accurate, rapid, and on-site visual detection of sulfite, in this study, we designed and synthesized a water-soluble near-infrared fluorescent probe LCMQ by integrating rhodamine with quinolinium. LCMQ specifically reacts with SO₂ through a 1,4-Michael addition, resulting in a high-contrast NIR fluorescence turn-on response accompanied by a distinct color change from purple to blue. LCMQ exhibits excellent water solubility, rapid response (<5 s), high sensitivity, and an ultra-low detection limit (0.78 nM), which enables it to rapidly and accurately detect SO₂ in food samples with high recovery (91.09-107.69%). In addition, the probe has been successfully applied to the situ imaging of SO₂ in food. Furthermore, we developed a sensing platform based on smartphone and paper sensing chip that can on-site visualize SO₂ in foods, demonstrating great potential for food safety surveillance.