Mitochondria-Targeting Fluorescent Probes for Hydrogen Sulfide Detection and Imaging.

Hydrogen sulfide (HS) is a potent redox-active signaling molecule commonly dysregulated in disease states. The production of HS and its involvement in various pathological conditions associated with mitochondrial dysfunction has been extensively documented. During stress, cystathionine gamma-lyase and cystathionine beta-synthase enzymes residing in cytosol are copiously translocated into the mitochondria to boost HS production, confirming its pivotal role in mitochondrial activities. However, report on HS levels in tissue, cells and organelles are lacking, mainly due to the absence of precise and accurate detection tools. Thus, there is a need to determine and monitor the levels of HS in this important organelle. Recently, fluorescent probes have been identified as efficient tools for detecting and monitoring the levels of various biomolecules of medical importance including biological thiols. The development of fluorescent probes is a multi-pronged approach involving coupling of fluorophores with responsive sites. The use of fluorescent probes for monitoring mitochondrial HS levels has recently received more attention, resulting in numerous publications depicting their synthesis, mechanism of action, application, and potential challenges. Fluorescent probes offer precise and timely results, high sensitivity, and selectivity, low biotoxicity, and minimal background interference. In this review, we aim to report designs of such probes, reaction mechanisms and their application in detecting mitochondrial HS levels. Fluorescent probes can help uncover physio/pathological levels of HS in essential organelles, its interactions with various biomarkers and associated consequences in biological systems.