An activatable ratiometric near-infrared fluorescent probe for hydrogen sulfide imaging in vivo

Abstract

Ratiometric fluorescent probes hold great promise for in vivo imaging; however, stimuli-activatable ratiometric probes with fluorescence emissions in near-infrared (NIR) region are still very few. Herein, we report a hydrogen sulfide (H2S)-activatable ratiometric NIR fluorescent probe (1-SPN) by integrating a H2S-responsive NIR fluorescent probe 1 into a H2S-inert poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b’]dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT)-based NIR semiconducting polymer nanoparticle (SPN). 1-SPN shows “always on” PCPDTBT fluorescence at 830 nm and weak probe 1 fluorescence at 725 nm under excitation at 680 nm. The ratio of NIR fluorescence intensities between 725 and 830 is small. Upon interaction with H2S, the fluorescence at 725 nm is rapidly switched on, resulting in a large enhancement of I725/I830, which is allowed for sensitive visualization and quantification of H2S concentrations in living cells. Taking advantage of enhanced tissue penetration depth of NIR fluorescence, 1-SPN is also applied for real-time ratiometric fluorescence imaging of hepatic and tumor H2S in living mice. This study demonstrates that activatable ratiometric NIR fluorescent probes hold great potential for in vivo imaging.