Ulcerative colitis imaging via a ratiometric fluorescent probe with large emission shift for SO₂ sensing

Sulfur dioxide (SO₂) serves as a gaseous signaling molecule that exerts pivotal regulatory functions in diverse physiological and pathological processes and has emerged as a novel gaseous biomarker associated with multiple inflammatory and hepatic diseases. Ulcerative colitis (UC), a diffuse inflammatory bowel disease primarily affecting the colonic mucosa, manifests as chronic inflammation. However, direct ratiometric visualization of SO₂ in UC lesions has remained challenging due to the scarcity of ratiometric fluorescent probes with large emission shifts suitable for in vivo imaging. Herein, we present SL, a ratiometric fluorescent probe that reports SO₂ via analyte-induced dual-emission rearrangement with a large spectral shift. Using SL, we captured dynamic SO₂ signals at the cellular level and visualized endogenous SO₂ changes in UC mice. These findings demonstrate that SL enables the examination of SO₂ dynamics in living systems and may facilitate investigations of SO₂-associated signaling events in inflammatory pathological contexts.