Near-Infrared Fluorescence Probe for in Situ Detection of Superoxide Anion and Hydrogen Polysulfides in Mitochondrial Oxidative Stress

H<sub>2</sub>S plays important physiological and pathological roles in the cardiovascular system and nervous system. However, recent evidence imply that hydrogen polysulfides (H<sub>2</sub>S<sub><i>n</i></sub>) are the actual signaling molecules in cells. Although H<sub>2</sub>S<sub><i>n</i></sub> have been demonstrated to be responsible for mediating tumor suppressors, ion channels, and transcription factors, more of their biological effects are still need to be elaborated. On one hand, H<sub>2</sub>S<sub><i>n</i></sub> have been suggested to be generated from endogenous H<sub>2</sub>S upon reaction with reactive oxygen species (ROS). On the other hand, H<sub>2</sub>S<sub><i>n</i></sub> derivatives are proposed to be a kind of direct antioxidant against intracellular oxidative stress. This conflicting results should be attributed to the regulation of redox homeostasis between ROS and H<sub>2</sub>S<sub><i>n</i></sub>. Superoxide anion (O<sub>2</sub><sup>•–</sup>) is undoubtedly the primary ROS existing in mitochondria. We reason that the balance of O<sub>2</sub><sup>•–</sup> and H<sub>2</sub>S<sub><i>n</i></sub> are pivotal in physiological and pathological processes. Herein, we report two near-infrared fluorescent probes Hcy-Mito and Hcy-Biot for the detection of O<sub>2</sub><sup>•–</sup> and H<sub>2</sub>S<sub><i>n</i></sub> in cells and in vivo. Hcy-Mito is conceived to be applied in mitochondria, and Hcy-Biot is designed to target tumor tissue. Both of the probes were successfully applied for visualizing exogenous and endogenous O<sub>2</sub><sup>•–</sup> and H<sub>2</sub>S<sub><i>n</i></sub> in living cells and in tumor mice models. The results demonstrate that H<sub>2</sub>S<sub><i>n</i></sub> can be promptly produced by mitochondrial oxidative stress. Flow cytometry assays for apoptosis suggest that H<sub>2</sub>S<sub><i>n</i></sub> play critical roles in antioxidant systems.