Carbon monoxide (CO) is an important gas signaling molecule and has been widely involved in regulating important life processes. Effective monitoring of CO in living systems is critical. Combined with the accuracy of ratio detection and the advantages of two-photon imaging, a simple ratiometric two-photon fluorescent probe RTFP was rationally designed and synthesized using 7-(diethylamino)-4-hydroxycoumarin as a two-photon fluorophore and allyl carbonate as the reactive unit. Probe RTFP exhibited excellent selectivity and sensitivity towards CO, and was successfully applied to image endogenous CO in living cells and zebrafish.

Carbon monoxide (CO), a potential therapeutic gaseous molecule for the treatment of inflammation-related diseases, is difficult to deliver directly into the body. CO-releasing molecule (CORM)-3 is an alternative molecule for in vivo delivery of CO. To track the distribution of CORM-3 in vitro and in vivo, we reasonably designed and synthesized a series of coumarin-pyridine dyads (1-3) by DFT calculation. Applying the 4-nitro-benzyl group as the recognition site, two new metal-free fluorescent probes (MFP-1/2) were used for CORM-3 detection. As expected, probe MFP-1/2 showed an obvious off-on fluorescent response after the reaction with CORM-3. Meanwhile, probe MFP-2 exhibited good selectivity and sensitivity to CORM-3 in PBS. With the aid of its large stock shift and red emitting wavelength, MFP-2 was successfully applied to track the distribution of CORM-3 in living cells and in mice.

Diabetes has emerged as a global health challenge and hydrogen sulfide (H2S) is thought to be related to diabetes. We herein reported a dual-locked near-infrared fluorescent probe (DLSP) to monitor the fluctuation of H2S in vitro and in vivo. DLSP displayed excellent selectivity and high sensitivity to H2S comparing with single-locked probes (SLSP-1/2). Using probe DLSP, the visualization of the biosynthesis of endogenous H2S production in insulin-resistant HepG2 cells (IR-HepG2 cells) and the fluctuation of H2S in diabetic mice was realized for the first time.

A novel single-component fluorescent probe HCP using N-acetylgalactosamine (GalNAc) as the hepatocyte-specific moiety and 3-nitrophthalimide as the fluorescent reactive unit was designed and synthesized to specifically detect hepatocellular carbon monoxide (CO) in vitro and in vivo. The spectral experimental results indicate that HCP displayed high selectivity to CO and could be used to detect trace CO in an aqueous solution with a prominent fluorescent response (more than 80 times). Bioimaging results show that HCP could specifically transport to asialoglycoprotein receptor overexpressed HepG2 cells and could image endogenous CO release in HepG2 cells and the liver of zebrafish in situ during acute liver injury.

Liver injury is typified by an inflammatory response. Hypochlorous acid (HClO), an important endogenous reactive oxygen species, is regarded as a biomarker associated with liver injury. Near-infrared (NIR) fluorescent probes with the advantage of deep tissue penetrating and low auto-fluorescence interference are more suitable for bioimaging in vivo . Thus, in this work, we designed and synthesized a novel NIR hepatocyte-specific fluorescent probe named NHF . The probe NHF showed fast response (< 3s), large spectral variation, and good selectivity to trace HClO in buffer solution. By employing N -acetylgalactosamine (GalNAc) as the targeting ligand, probe NHF can be actively delivered to the liver tissue of zebrafish and mice. It is important that probe NHF is the first NIR hepatocyte-specific fluorescent probe, which successfully visualized the up-regulation of endogenous HClO in the oxygen-glucose deprivation/reperfusion (OGD/R) model HepG2 cells and dynamically monitored APAP-induced endogenous HClO in the liver tissue of zebrafish and mice.