A novel precipitating-fluorochrome-based fluorescent probe for monitoring carbon monoxide during drug-induced liver injury

Carbon monoxide (CO), as one of significant gas transmitter, is closely associated with a variety of physiological and pathological processes. Although plenty of fluorescent probes have been prepared for detecting CO, most of them suffer from water-soluble fluorophores and short emission wavelength, which tends to diffuse and is limited to apply in vivo. Herein, a novel water-soluble fluorescent probe (HPQ-MQ-CO) is prepared to detect CO by releasing a precipitating fluorochrome (HPQ-MQ-OH), which is developed by introducing the 1-ethyl-2-methylquinoline group into HPQ to obtain long emission wavelength and good diffusion resistant ability. Allyl formate, as the identification unit of CO, has good water solubility and quenches the fluorescence of HPQ-MQ-CO. When the probe reacts with CO and Pd2+, an long-emission and solid-state fluorescence signal at 650 nm can be observed, which is based on excited-state intramolecular proton transfer (ESIPT) mechanism. When the concentration of CO is raised to 100.0 μM, the fluorescence is increased 29 times, indicating the sensitivity of the probe. Moreover, this probe shows prominent selectivity for CO compared with other interfering species. Given these advantages, HPQ-MQ-CO can be used for CO detection in HepG2 cells and zebrafish by in-situ and long-term fluorescence imaging. In addition, this probe can monitor the up-regulation of CO in HepG2 cells and zebrafish during drug-induced liver injury (DILI).