Fluorescent probes for detecting and imaging mitochondrial hydrogen sulfide.

Hydrogen sulfide (H₂S) is a potent redox-active signaling molecule commonly dysregulated in disease states. The production of H₂S and its involvement in various pathological conditions associated with mitochondrial dysfunction have extensively documented. During stress, cystathionine gamma-lyase and cystathionine beta-synthase in cytosol are copiously translocated into the mitochondria to boost H₂S production, confirming its pivotal role in mitochondrial activities. However, little study has been done on H₂S levels in tissues, cells and organelles, mainly due to the absence of precise and accurate detection tools. Thus, there is an urgent need to determine and monitor the levels of H₂S in these important organelles. Fluorescent probes are efficient tools for detecting and monitoring various important biomolecules including biological thiols. The development of fluorescent probes is a multi-pronged approach which involves coupling fluorophores with responsive sites. The use of fluorescent probes for monitoring mitochondrial H₂S levels has recently received widespread 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 H₂S levels. Fluorescent probes can help uncover physio/pathological levels of H₂S in essential organelles, its interactions with various biomarkers and associated consequences in biological systems.