In Situ Activatable Ratiometric NIR-II Fluorescence Nanoprobe for Quantitative Detection of H₂S in Colon Cancer

As key characteristic molecules, several H₂S-activated probes have been explored for colon cancer studies. However, a few ratiometric fluorescence (FL) probes with NIR-II emissions have been reported for the quantitative detection of H₂S in colon cancer in vivo. Here, we developed an in situ H₂S-activatable ratiometric nanoprobe with two NIR-II emission signals for the detection of H₂S and intelligently lighting up colon cancer. The nanoprobe comprised a down conversion nanoparticle (DCNP), which emitted NIR-II FL at 1550 nm on irradiation with a 980 nm laser (F_{1550Em, 980Ex}). Further, human serum albumin (HSA) was combined with Ag⁺ on the surface of DCNP to form a DCNP@HSA-Ag⁺ nanoprobe. In the presence of H₂S, Ag₂S quantum dots (QDs) were formed in coated HSA, which emitted FL at approximately 1050 nm on irradiation with an 808 nm laser (F_{1050Em, 808Ex}) through an H₂S-induced chemical reaction between H₂S and Ag⁺; however, the FL signal of DCNP was stable at 1550 nm (F_{1550Em, 980Ex}), generating a H₂S concentration-dependent ratiometric F_{1050Em, 808Ex}/F_{1550Em, 980Ex} signal. The NIR-II ratiometric nanoprobe was successfully used for the accurate quantitative detection of H₂S and the detection of the precise location of colon cancer through an endogenous H₂S-induced in situ reduction reaction to form Ag₂S QDs. Thus, these findings provide a new strategy for the specific detection of targeted molecules and diagnosis of disease based on the in situ-activatable NIR-II ratiometric FL nanoprobe.