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

H₂S plays important physiological and pathological roles in the cardiovascular system and nervous system. However, recent evidence imply that hydrogen polysulfides (H₂S_n) are the actual signaling molecules in cells. Although H₂S_n 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, H₂S_n have been suggested to be generated from endogenous H₂S upon reaction with reactive oxygen species (ROS). On the other hand, H₂S_n 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 H₂S_n. Superoxide anion (O₂^•–) is undoubtedly the primary ROS existing in mitochondria. We reason that the balance of O₂^•– and H₂S_n are pivotal in physiological and pathological processes. Herein, we report two near-infrared fluorescent probes Hcy-Mito and Hcy-Biot for the detection of O₂^•– and H₂S_n 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 O₂^•– and H₂S_n in living cells and in tumor mice models. The results demonstrate that H₂S_n can be promptly produced by mitochondrial oxidative stress. Flow cytometry assays for apoptosis suggest that H₂S_n play critical roles in antioxidant systems.