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CO, a gas molecule that is harmful to living organisms, has a high affinity with hemoglobin, which will cause severe hypoxia. However, in recent years, researchers have discovered that endogenous CO, similar to NO, is one of the messenger molecules, which has a certain regulatory effect in many physiological and pathological processes in the respiratory system, cardiovascular system, and nervous system. Therefore, it is urgent to explore an effective method to monitor the role of CO under physiological and pathological conditions. Herein, we designed and synthesized a near-infrared small-molecule fluorescent probe for the detection of CO in living cells. In this design, a two-site BODIPY dye was introduced as the fluorophore, and the allyl chloroformate part as the CO reactive group. The probe displays excellent sensitivity, selectivity, and a good linear relationship to CO. Furthermore, it shows good biocompatibility and low cytotoxicity. This probe has been successfully applied to the detection of CO in a variety of cells. The developed fluorescent probe can serve as a potential molecular imaging tool for in vivo imaging and detection of CO.

Hydrogen polysulfides (H2Sn, n ≥ 2) is recently regarded as a potential signaling molecule which shows a higher efficiency than hydrogen sulfides (H2S) in regulating enzymes and ion channels. However, the development of specific fluorescent probes for H2Sn with long-wavelength emission (>600 nm) are still rare. In this work, a semi-naphthorhodafluor-based red-emitting fluorescent probe SNARF-H2Sn containing a phenyl 2-(benzoylthio) benzoate responsive unit was constructed. SNARF-H2Sn was capable of selectively detecting H2Sn over other reactive sulfur species. Treatment with H2Sn would result in a > 1000-fold fluorescence enhancement within 10 min. SNARF-H2Sn showed a low limit of detection down to 6.7 nM, and further enabled to visualize exogenous/endogenous H2Sn in living A549 cells and zebrafish.

Sulfur dioxide (SO2), a possible endogenous gaseous signaling molecule, has been found to be correlated with various diseases in living organisms. Thus, the development of effective methods for detection of SO2 are of great physiological and pathological significance. In this work, we report a ratiometric NIR fluorescent probe Cou-Rh for monitoring bisulfite on basis of Michael addition reaction. This probe is prepared from coumarin by acid-catalyzed cyclization reaction. The addition of bisulfite results in a significant decrease of fluorescence intensity at 695 nm and enhancement at 550 nm. The probe also displays high selectivity over various biologically related analytes with nanomolar limit of detection. What’s more, fluorescence imaging further confirms that the probe is capable of detecting bisulfite in living cells and zebrafish larvae. The results demonstrate that probe Cou-Rh can be employed for a useful scaffold to study the physiological function of sulfur dioxide.