Baoli Dong

Development of a Two‐Photon Fluorescent Probe for Imaging of Endogenous Formaldehyde in Living Tissues

Investigation of the physiological and pathological functions of formaldehyde (FA) are largely restricted by a lack of useful FA imaging agents, in particular, those that allow detection of FA in the context of living tissues. Herein, we present the rational design, synthesis, and photophysical property studies of the first two-photon fluorescent FA probe, Na-FA. Importantly, the highly desirable attributes of the probe Na-FA (such as a very large turn-on signal (up to 900-fold), a low detection limit, and a very fast onset imparted by the unique design aspects of the probe), make it possible to monitor endogenous FA in living tissues for the first time. Furthermore, sodium bisulfite was identified as a simple and convenient inhibitor of FA within biological environments.

Fluorescent chemosensors manipulated by dual/triple interplaying sensing mechanisms

Fluorescence imaging is a powerful approach for noninvasive and real-time visualization and tracking of biomolecules and biological processes in living systems. The fluorescent chemosensors with dual/triple interplaying sensing mechanisms tend to provide diverse fluorescence signals or amplify the response signals, which are propitious to simultaneously track multiple analytes or to improve the selectivity and sensitivity of the chemosensors. Thus, the development of dual/triple sensing mechanism-based chemosensors has attracted great interest recently. This review highlights the representative cases of the fluorescent chemosensors with dual/triple interplaying sensing mechanisms published since 2010, and these chemosensors are classified according to the types of the interplaying sensing mechanisms, including ICT-FRET, PET-FRET, PET-ICT-ESIPT, etc.

Simultaneous Near-Infrared and Two-Photon In Vivo Imaging of H2O2 Using a Ratiometric Fluorescent Probe based on the Unique Oxidative Rearrangement of Oxonium

A new ratiometric fluorescent H2 O2 probe, benzopyrylium-coumarin (BC), is designed by using an oxonium moiety as the unique H2 O2 response site. The BC probe exhibits an extremely large emission shift of 221 nm in response to H2 O2 , and is successfully applied for the simultaneous near-infrared and two-photon imaging of H2 O2 in living cells, mouse-liver tissues, and zebrafish.

Corrigendum: Construction of a Near-Infrared Fluorescent Turn-On Probe for Selenol and Its Bioimaging Application in Living Animals.

As selenocysteine (Sec) carries out the majority of the functions of the various Se-containing species in vivo, it is of high importance to develop reliable and rapid assays with biocompatibility to detect Sec. Herein, an NIR fluorescent turn-on probe for highly selective detection of selenol was designed and synthesized. The probe exhibits large turn-on signal upon treatment with selenocysteine (R-SeH), and it was further demonstrated that the new NIR fluorescent probe can be employed to image selenol in living animals.

Tuning solid-state fluorescence of pyrene derivatives via a cocrystal strategy

1-Acetyl-3-(4-methoxyphenyl)-5-(1-pyrenyl)-pyrazoline (AMPP) was synthesized and crystallized to yield three types of crystals with different host–guest structures: AMPP crystal (I), AMPP–phenol (II) and AMPP–(2-naphthol) cocrystals (III). Twisted π-conjugated structures and different stacking modes of AMPP molecules were found in the three crystals. In crystal I, pyrene fluorophores adopt a face-to-face π-stacked arrangement, while pyrene fluorophores in crystals II and III adopt the monomer arrangements because AMPPs were widely separated by means of entrapment of guest molecules in the two lattices. Investigation of the optical-properties of the three crystals reveals that they are closely related to the arrangements of the pyrene fluorophores. Face-to-face π–π stacking of the pyrene fluorophores in crystal I cause a broad band emission with a red shift of 40–50 nm relative to pyrene fluorescence in solution. However, the emission spectrum of crystal II is similar to that of crystal III; both of them exhibit two sharp bands with a small red shift of 20 nm relative to pyrene fluorescence in solution, which are induced by the monomer arrangements of pyrene fluorophores and overlaps of π-orbitals between benzene and pyrene fluorophores. These results demonstrate that using a cocrystal strategy to regulate packing modes of pyrene fluorophores is an effective way for exploring highly blue-emissive pyrene derivatives.

Development of green to near-infrared turn-on fluorescent probes for the multicolour imaging of nitroxyl in living systems

Nitroxyl (HNO) is one of the important reactive nitrogen species (RNS) and show significant biological activities with significant therapeutic potential. Herein, three novel turn-on probes (NP-1-3) based on structurally related dyes with different emission colors as fluorescent scaffolds have been developed for detecting HNO in biological systems. The probes exhibit high sensitivity, excellent selectivity, desirable performance at physiological pH and low cytotoxicity. By incubating living cells with these probes simultaneously, we demonstrate the multicolor imaging of HNO with emission colors in the range of green to near-infrared (NIR) in living systems for the first time. Furthermore, probe NP-3 responds to HNO with a significant turn-on NIR fluorescence signal upon excitation in the NIR region, and it is successfully applied for sensing HNO in living mice.

A tumor-targeting and lysosome-specific two-photon fluorescent probe for imaging pH changes in living cells

Lysosomal pH is closely related to the metastasis and apoptosis of cancer cells. Detecting lysosomal pH changes in cancer cells could be helpful for analyzing tumor progressions and in-depth study of the roles of lysosomes in tumor invasion and metastasis. Herein, we describe a novel tumor-targeting and lysosome-specific two-photon fluorescent probe (BN-lys) for imaging pH changes for the first time. Biotin was employed as the tumor-targeting module, and morpholine was selected as the lysosome-specific group and the pH site to control the fluorescence by photoinduced electron transfer (PET) mechanism. With a pKa value of 5.36, BN-lys showed a fast and reversible fluorescence response to pH. Under the guidance of the biotin group, BN-lys displayed strong one-photon and two-photon fluorescence responses to lysosomal pH in cancer cells, while it displayed weak fluorescence in normal cells. Furthermore, BN-lys could be applied for the imaging of chloroquine-stimulated lysosomal pH changes in living cells. These features demonstrate that this probe could have practical applications in biological research.

Two-photon red-emissive fluorescent probe for imaging nitroxyl (HNO) in living cells and tissues

Nitroxyl (HNO) plays important roles in the regulation of many physiological and pathological processes, and can serve as a potential therapeutic agent for cardiovascular disease. The development of HNO detection in living systems is greatly important for in-depth studies of its biosynthesis and activities. Herein, we describe a novel two-photon red-emissive fluorescence probe (RP) for imaging HNO in living cells and tissues. RP was based on a red-emissive dye, Rho, and showed no fluorescence. When responding to HNO, RP can emit red fluorescence with the emission wavelength at 638 nm. RP exhibited a sensitive and selective response to HNO. Theoretical calculations demonstrated that the overlaps between the HOMO and LUMO were large for Rho and tiny for RP, consistent with the absorption and fluorescence properties of Rho and RP. Assisted by three-dimensional (3D) imaging, the two-photon imaging of HNO with red emission color in living tissues was successfully performed.

Synthesis, photoluminescence properties and theoretical insights on 1,3-diphenyl-5-(9-anthryl)-2-pyrazoline and -1H-pyrazole.

1,3-Diphenyl-5-(9-anthryl)-2-pyrazoline and 1,3-diphenyl-5-(9-anthryl)-1H-pyrazole with an anthryl chromophore were synthesized and characterized using (1) H NMR, (13) C NMR, FT-IR, mass spectrometry and elemental analysis. Their optical properties were characterized by UV-vis absorption and fluorescence spectroscopy. It was observed that the absorption and fluorescence spectra of the two compounds showed a red shift with respect to that of anthracene. Pyrazole exhibited high fluorescent quantum yields (Φf  = 0.90 in toluene) while pyrazoline showed nearly no fluorescence in solution. The significant fluorescence divergence of the two similar compounds was investigated theoretically through density functional theory (DFT) calculations. The energetically lowest-lying state S1 in the pyrazoline exhibited both characteristics of locally excited and electron-transfer states that resulted in the fluorescence quenching of anthryl chromophore whereas the S1 state in the pyrazole corresponded to an optically allowed state that led to high fluorescence quantum yields in solutions.

Construction of a ratiometric fluorescent probe with an extremely large emission shift for imaging hypochlorite in living cells

Hypochlorite is one of the important reactive oxygen species (ROS) and plays critical roles in many biologically vital processes. Herein, we present a unique ratiometric fluorescent probe (CBP) with an extremely large emission shift for detecting hypochlorite in living cells. Utilizing positively charged α,β-unsaturated carbonyl group as the reaction site, the probe CBP itself exhibited near-infrared (NIR) fluorescence at 662nm, and can display strong blue fluorescence at 456nm when responded to hypochlorite. Notably, the extremely large emission shift of 206nm could enable the precise measurement of the fluorescence peak intensities and ratios. CBP showed high sensitivity, excellent selectivity, desirable performance at physiological pH, and low cytotoxicity. The bioimaging experiments demonstrate the biological application of CBP for the ratiometric imaging of hypochlorite in living cells.