Mitochondrial-Targeted Ratiometric Near-Infrared Fluorescence Probe for Monitoring Nitric Oxide in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a destructive autoimmune disease, where nitric oxide (NO) is closely implicated in the inflammatory processes of RA. Therefore, direct visualization of NO is essential to assess the pathological changes in RA. Herein, a mitochondrial-targeted near-infrared ratiometric fluorescent probe (NFL-NH₂), based on the intramolecular charge transfer effect, was synthesized and applied to monitor the changes of NO content in early RA. Specially, probe NFL-NH₂ showed a 44-fold fluorescent intensity ratio (I₇₀₅/I₇₈₀) response toward NO with a detection limit of 0.536 nM, enabling qualitative and quantitative analysis of NO. Additionally, NFL-NH₂ can accurately target mitochondria and sensitively detect exogenous and endogenous NO in RAW 264.7 cells. Notably, in vivo RA monitoring assays demonstrated that NFL-NH₂ can rapidly detect NO levels associated with the inflammatory damage degree in RA mice models by ratiometric fluorescence imaging. These results validate that NFL-NH₂ holds significant potential for diagnosing NO-mediated RA diseases.