Fluorescent Probe Based on Azobenzene-Cyclopalladium for the Selective Imaging of Endogenous Carbon Monoxide under Hypoxia Conditions.

Carbon monoxide (CO), a crucial gas message molecule, plays an important role in the regulation of physiological and pathological process. Hypoxia-induced CO is involved in modulating various cellular activities, including signal transduction, proliferation, and apoptosis. However, tracking CO fluctuation in the hypoxic cells is still a challenge due to lack of straightforward, visualized, and noninvasive tools. In this work, based on metal palladium-catalyzed reaction, we present the rational design, synthesis, and biological utility of an azobenzene-cyclopalladium-based fluorescent probe, ACP-2, for CO monitoring. ACP-2 exhibits capacity of detecting CO in aqueous buffer solution and live cells with high sensitivity and specificity. Utilizing ACP-2, we displayed a direct and visual evidence of endogenous CO up-regulation in live cells induced by hypoxia. Moreover, CO up-regulation during oxygen-glucose deprivation/reperfusion (OGD/R) was also imaged and certified by ACP-2.