Molecular design of hydrogen sulfide probes and their bioimaging applications

Hydrogen sulfide (H₂S) has garnered increasing attention in recent years, not only as a hazardous environmental pollutant but also as the third endogenous gas signaling molecule, alongside nitric oxide and carbon monoxide. At elevated concentrations, it poses serious threats to human health by irritating the respiratory tract and nervous system, with high-level exposure potentially leading to coma or even death. Conversely, at physiological levels, H₂S participates in a variety of essential biological processes, including cardiovascular regulation, neuroprotection and cellular metabolism. Given this dual nature, reliable monitoring of H₂S concentrations in both biological matrices and environmental samples is of considerable significance. Fluorescent probes have emerged as powerful analytical tools for this purpose, owing to their high sensitivity, excellent spatiotemporal resolution and non-invasive imaging capabilities. By exploiting the intrinsic chemical features of H₂S, such as nucleophilicity, reducing potency and affinity for metal ions, a diverse array of fluorescent sensors has been developed over the past few years. This review aims to provide a systematic overview of recent progress in the design and application of these probes, with particular emphasis on their distinct response mechanisms and their utility in H₂S sensing and bioimaging. Representative examples from each category are discussed, and the strengths and limitations of different strategies are compared. Through this summary, we hope to offer useful insights for the future development of more advanced H₂S probes tailored to specific research or diagnostic needs.