Research Progress of Near-Infrared Fluorescent Probes for Hydrogen Sulfide

Hydrogen sulfide (H2S) is a colorless gas with the unpleasant smell of rotten eggs. It not only exists in the environment but was also considered the third important endogenous gaseous transmitter following nitric oxide (NO) and carbon monoxide (CO) in biological systems. H2S has recently attracted more attention for contributing to human health and disease. H2S has important biological functions and has been recognized as a cytoprotectant and gasotransmitter in many tissue types, including mediating vascular tone in blood vessels and neuromodulation in the brain. Hydrogen sulfide concentration has been demonstrated to be closely correlated with particular diseases in modern medical research, such as diabetes, Alzheimer's disease and Parkinson's disease. The molecular mechanisms by which H2S affects cell signaling and other physiological events remain unclear. Therefore, it is necessary to develop highly sensitive and selective methods for detecting the concentration of H2S in living cells and organisms. The near-infrared fluorescent probe for detecting H2S has been the research hotspot. Near-infrared (NIR) fluorescent probes have several significant advantages for imaging applications in vivo : negligible photodamage, deep tissue penetration, and low interference from background auto fluorescence. Many new methods for visualizing H2S in living systems have been reported. At the molecular level, H2S exhibits unique chemical characteristics, acting as a good reducing agent and a good nucleophile. Thus the main strategies used in NIR fluorescent probe development for H2S detection include azide and nitro group reduction, nucleophilic attack, addition reaction, etc. Herein, the design and synthesis, recognition mechanism, properties of NIR fluorescent probes for H2S and their fluorescence imaging in cells and organisms and the latest research progress reported in recent three years have been reviewed. Finally, in our opinion, the future research direction and development trend of this kind of probes are prospect.