A near-infrared frequency upconversion fluorescent probe for rapid and sensitive visual detection of sulfur dioxide†

Inflammation is a complex physiological response involving various cellular and molecular events. Sulfur dioxide (SO₂), which is usually in the form of HSO₃⁻ and SO₃²⁻ under physiological conditions, plays a crucial role in the regulation of inflammation and diseases. Frequency upconversion luminescence (FUCL) can realize the unique anti-Stokes process of long-wavelength excitation to short-wavelength emission; thus, it is a highly promising optical method for in vivo imaging due to its deep tissue penetration, low photo-damage, etc. Therefore, we developed a near-infrared FUCL NIRX-1 probe for the detection of HSO₃⁻. NIRX-1 had a fast response (80 s), a low detection limit (0.43 μM), and high selectivity towards HSO₃⁻. In addition, NIRX-1 had deep light penetration ability due to the near-infrared excitation at 808 nm and was able to detect HSO₃⁻ in living cells and mice. Lastly, NIRX-1 was employed in the imaging of HSO₃⁻ in an inflammation mouse model through FUCL imaging techniques. All these features make NIRX-1 a good candidate for the investigation of SO₂-associated physiological and pathological processes.