A FRET probe based on flavonol-benzothiazole for the detection of viscosity and SO2 derivatives.

Sulfur dioxide (SO₂) and viscosity play important roles in living organisms, and abnormal levels of them are associated with many diseases. Hence, a bifunctional fluorescence probe (E)-3-(2-(4-(4-(4-(6-fluoro-3-hydroxy-4-oxo-4H-chromen-2-yl)benzoyl)piperazin-1-yl)styryl)benzo-[d]thiazol-3-ium-3-yl)propane-1-sulfonate (HFBT) with fluorescence resonance energy transfer (FRET) properties was successfully constructed by using 3-hydroxyflavonol as the energy donor and benzothiazole sulphonate derivatives as the energy acceptor, and it can be used for the detection of SO₂ derivatives (HSO₃^-/HSO₃^2-) and viscosity. HFBT exhibits a large Stokes shift (245 nm), high resonance energy transfer efficiency (95.56 %), and excellent selectivity, anti-interference and low limit of detection (LOD = 0.057 μM) for HSO₃^-. The fluorescence intensity of HFBT at 596 nm gradually increases with the increase of viscosity. Interestingly, a visual HSO₃^- detection platform was successfully constructed and applied to the quantitative detection of HSO₃^- in food. Additionally, HFBT was successfully applied to imaging endogenous and exogenous HSO₃^- in cells. The successful development of HFBT provides an effective tool for the detection and imaging of HSO₃^- in food and cells.