Targeted imaging of superoxide anion with a near-infrared fluorescent probe for tumor precise diagnosis

Superoxide anion (O2•−) is a key reactive oxygen species involved in oxidative stress–related diseases and is typically overproduced in tumor cells, making it an important biomarker for cancer diagnosis. Herein, we report a near-infrared (NIR) turn-on fluorescent molecular probe, Cy- O2•−, for selective imaging of O2•− and precise tumor identification. Cy-O2•− is rationally designed based on a hemicyanine fluorophore, in which a trifluoromethanesulfonate group serves as a specific O2•−-responsive recognition unit. In its intact form, fluorescence is effectively suppressed by blocking the intramolecular charge transfer (ICT) process. Upon reaction with O2•−, nucleophilic attack at the sulfonyl sulfur induces O–S bond cleavage, releasing the free hemicyanine fluorophore, thereby recovering the NIR fluorescence signal (∼742 nm). Cy-O2•− exhibits high sensitivity, excellent selectivity toward O2•− over other reactive species, and good biocompatibility. Cellular experiments demonstrate its capability to monitor endogenous and exogenous O2•− fluctuations. More importantly, in vivo imaging in tumor-bearing mouse models confirms precise tumor visualization, highlighting its potential for early tumor