Construction of NIR and Ratiometric Fluorescent Probe for Monitoring Carbon Monoxide under Oxidative Stress in Zebrafish

Carbon monoxide (CO), as a crucial gasotransmitter, is endogenously produced by the degradation of heme and plays a critical role in regulating various physiological and pathophysiological processes such as oxidative stress. Thus, an effective fluorescent probe for investigating the relationships between CO and oxidative stress in vivo is necessary. In this paper, a ratiometric near-infrared (NIR) fluorescent probe (CP-CO) based on a coumarin-benzopyran fluorophore for imaging CO is developed. CP-CO itself displays strong coumarin emission due to its spironolactone structure. After the probe is reacted with CO and PdCl2, a notable enhancement of emission intensity at 690 nm can be found, which results in an obvious red shift of emission (200 nm). Moreover, CP-CO exhibits high sensitivity toward CO and produces a high enhancement ratio (203-fold). In addition, the probe is applied for ratiometric monitoring of exogenous and endogenous CO levels in HepG2 cells. Furthermore, the fluorescence imaging of CP-CO in zebrafish is performed by two-photon excitation along with excellent penetration ability. Most importantly, CP-CO can visualize the upregulation of CO under lipopolysaccharide (LPS)-induced oxidative stress in a zebrafish model, which vividly reveals its excellent ability in the elucidation of CO function in related biological events.