Sulfonate-modified cyanine probe enables real-time monitoring of oxidative stress in colitis via hydroxyl radical-specific fluorescence turn-on

Hydroxyl radicals (·OH) are pivotal in inflammatory diseases but difficult to detect in vivo. We developed a near-infrared probe (Re-Cy7-SO₃H) based a sulfonated cyanine dye, which shows ·OH-specific fluorescence activation at 800 nm through oxidative CN bond cleavage and structural planarization. Density functional theory calculations confirmed enhanced intramolecular charge transfer upon planarization. The probe demonstrated excellent water solubility (logP = −4.333), selectivity (R² = 0.987), and biosafety (>90 % viability at 25 μM), enabling real-time ·OH monitoring in lipopolysaccharide (LPS) stimulated macrophages and dextran sulfate sodium (DSS) induced colitis mice. In vivo imaging revealed disease severity-dependent fluorescence, with 2.5 % DSS-treated mice showing 3.2-fold higher colonic signals than controls at 90 min.