Sensing and Bioimaging of the Gaseous Signaling Molecule Hydrogen Sulfide by Near-Infrared Fluorescent Probes

A fluorescent probe for the monitoring of H2S levels in living cells and organisms is highly desirable. In this regard, near-infrared (NIR) fluorescent probes have emerged as a promising tool. NIR-I and NIR-II probes have many significant advantages; for instance, NIR light penetrates deeper into tissue than light at visible wavelengths, and it causes less photodamage during biosample analysis and less autofluorescence, enabling higher signal-to-background ratios. Therefore, it is expected that fluorescent probes having emission in the NIR region are more suitable for in vivo imaging. Consequently, a considerable increase in reports of new H2S-responsive NIR fluorescent probes appeared in the literature. This review highlights the advances made in developing new NIR fluorescent probes aimed at the sensitive and selective detection of H2S in biological samples. Their applications in real-time monitoring of H2S in cells and in vivo for bioimaging of living cells/animals are emphasized. The selection of suitable dyes for designing NIR fluorescent probes, along with the principles and mechanisms involved for the sensing of H2S in the NIR region, are described. The discussions are focused on small-molecule and nanomaterials-based NIR probes.