Highly selective imaging of intratumoral hydrogen sulfide by NIR-II emissive fluorescent probes

Hydrogen sulfide (H₂S) is an important signaling molecule that exists in a variety of tissues and has important effects on various physiological functions of the human body. Studies have shown that chronic kidney disease, liver cirrhosis and cardiovascular disease are closely related to abnormal levels of H₂S in the body. In addition, endogenous H₂S is closely associated with a variety of cancers and can be regarded as a biomarker for specific cancers. In this study, we have successfully designed a rhodamine hybrid polymethine-based small molecule dye (FL-NO₂), whose fluorescence in the second near-infrared window (NIR-II, 900–1700 nm) can be dramatically enhanced after exposure to H₂S. After being encapsulated by amphiphilic polymer F-127, the obtained water-soluble nanoparticles (n-FL-NO₂) can be used for the sensitive detection of H₂S in the NIR-II region, which provides large penetration depth and high signal-to-noise ratio. The probe also exhibited high selectivity towards H₂S, avoiding interference from multiple biothiols. The detection of endogenous H₂S in vivo was demonstrated with a colon cancer model, which expressed a high level of H₂S. In summary, this study provides a promising NIR-II fluorescent probe for the rapid detection of H₂S, which may become an effective tool for disease diagnosis.