To elucidate the complex role of biological H2S and study the mitochondrial damage and some related diseases, effective methods for visualization of H2S in mitochondria and in vivo are urgently needed. In this contribution, a novel near-infrared mitochondria-targetable fluorescence probe MI-H 2 S for H2S detection was developed. MI-H 2 S shows rapid detection ability for H2S in pure aqueous solution and outputs a highly selective and sensitive fluorescence-on signal at 663 nm with a large Stokes shift of 141 nm. Bioimaging experiments revealed that the probe has good mitochondrial-targeting ability and high-contrast imaging ability for detecting H2S in living systems. The probe also showed great potential in the detection of H2S during inflammation. All of the results demonstrate that MI-H 2 S can be applied as an effective probe for the visualization and study of H2S in mitochondria and in vivo.

Mitophagy is a vital cellular process playing vital roles in regulating cellular metabolism and mitochondrial quality control. Mitochondrial viscosity is a key microenvironmental index, closely associated with mitochondrial status. To monitor mitophagy and mitochondrial viscosity, three molecular rotors (Mito-1, Mito-2, and Mito-3) were developed. All probes contain a cationic quinolinium unit and a C12 chain so that they can tightly bind mitochondria and are not affected by the mitochondrial membrane potential. Optical studies showed that all probes are sensitive to viscosity changes with an off–on fluorescence response, and Mito-3 shows the best fluorescence enhancement. Bioimaging studies showed that all these probes can not only tightly locate and visualize mitochondria with near-infrared fluorescence but also effectively monitor the mitochondrial viscosity changes in cells. Moreover, Mito-3 was successfully applied to visualize the mitophagy process induced by starvation, and mitochondrial viscosity was found to show an increase during mitophagy. We expect Mito-3 to become a useful imaging tool for studying mitochondrial viscosity and mitophagy.

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