Red Emitting Neutral Fluorescent Glycoconjugates for Membrane Optical Imaging

Chitosan-bodipy macromolecular fluorescent probes prepared by click reactions for highly sensitive and selective recognition of 2,4-dinitrophenylhydrazine

Chitosan-based probes were prepared and they could identify 2,4-dinitrophenylhydrazine (DNH). CC bonds formed in a click reaction act as recognizing sites for DNH.

Fabrication of small-structure red-emissive fluorescent probes for plasma membrane enables quantification of nuclear to cytoplasmic ratio in live cells and tissues

Nuclear to cytoplasmic ratio is one of the vital parameters in diagnosis of cancer by means of hematoxylin-eosin (HE) stained histopathology. However, HE histopathology dependent on mechanical tissue slice damages biosamples and exhibits insufficient accuracy. Herein, we rationally prepared two small-molecule plasma membrane fluorescent probes with red-emitting fluorescence for visualizing plasma membrane in living cells and tissues. Their fluorescence intensities are strongly affected by environmental viscosity, which enables the exclusive imaging of plasma membrane in high fidelity. The probes can visualize plasma membrane in SiHa and rat blood red cells. Particularly, the probes are able to visualize T-tubule (transverse tubule) in skeletal muscle tissues successfully, suggesting their ability to image plasma membrane in tissues. In cooperation with Hoechst 33342, the nuclear to cytoplasmic ratio was successfully qualified in live cells and tissues. We believe these probes may have potential applications in facilitating the study on histopathology and the related areas.

Hybrid multimodal contrast agent for multiscale in vivo investigation of neuroinflammation

Neuroinflammation is a process common to several brain pathologies. Despites its medical relevance, it still remains poorly understood; there is therefore a need to develop new in vivo preclinical imaging strategies to monitor inflammatory processes longitudinally. We here present the development of a hybrid imaging nanoprobe named NP3, that was specifically designed to get internalized by phagocytic cells and imaged in vivo with MRI and bi-photon microscopy. NP3 is composed of a 16 nm core of gadolinium fluoride (GdF3), coated with bisphosphonate polyethylene glycol (PEG) and functionalized with a Lemke-type fluorophore. It has a hydrodynamic diameter of 28 ± 8 nm and a zeta potential of -42 ± 6 mV. The MR relaxivity ratio at 7 T is r1/r2 = 20; therefore, NP3 is well suited as a T2/T2* contrast agent. In vitro cytotoxicity assessments performed on four human cell lines revealed no toxic effects of NP3. In addition, NP3 is internalized by macrophages in vitro without inducing inflammation or cytotoxicity. In vivo, uptake of NP3 has been observed in the spleen and the liver. NP3 has a prolonged vascular remanence, which is an advantage for macrophage uptake in vivo. The proof-of-concept that NP3 may be used as a contrast agent targeting phagocytic cells is provided in an animal model of ischemic stroke in transgenic CX3CR1-GFP/+ mice using three complementary imaging modalities: MRI, intravital two-photon microscopy and phase contrast imaging with synchrotron X-rays. In summary, NP3 is a promising preclinical tool for the multiscale and multimodal investigation of neuroinflammation.

A dicyanoisophorone-based highly sensitive and selective near-infrared fluorescent probe for sensing thiophenol in water samples and living cells

Thiophenol (PhSH) is an important sulfhydryl compound in organic synthesis, but it is also a volatile environmental pollutant with high toxicity to organisms. Herein, we reported a novel near-infrared (NIR) probe (1) for turn-on fluorescence detection of PhSH. The probe was prepared by coupling 2,4-dinitrophenyl (DNP) to a dicyanoisophorone-based fluorophore (2). PhSH can specifically perform a nucleophilic aromatic substitution on probe 1 and result in the release of fluorophore 2, thus achieving a turn-on fluorescence response (λ_em = 693 nm). A dramatic color change from red (λ_abs = 525 nm) to blue (λ_abs = 668 nm) was also observed. This fluorescent assay displayed a large Stokes shift (∼133 nm) and a high sensitivity for PhSH, as well as a low detection limit (34 nM). Moreover, probe 1 was successfully applied to monitor PhSH in real water samples and image PhSH in living cells.

DANPY (dimethylaminonaphthylpyridinium): an economical and biocompatible fluorophore

Dyes with nonlinear optical (NLO) properties enable new imaging techniques and photonic systems. We have developed a dye (DANPY-1) for photonics applications in biological substrates such as nucleic acids; however, the design specification also enables it to be used for visualizing biomolecules. It is a prototype dye demonstrating a water-soluble, NLO-active fluorophore with high photostability, a large Stokes shift, and a favorable toxicity profile. A practical and scalable synthetic route to DANPY salts has been optimized featuring: (1) convergent Pd-catalyzed Suzuki coupling with pyridine 4-boronic acid, (2) site-selective pyridyl N-methylation, and (3) direct recovery of crystalline intermediates without chromatography. We characterize the optical properties, biocompatibility, and biological staining behavior of DANPY-1. In addition to stability and solubility across a range of polar media, the DANPY-1 chromophore shows a first hyperpolarizability similar to common NLO dyes such as Disperse Red 1 and DAST, a large two-photon absorption cross section for its size, substantial affinity to nucleic acids in vitro, an ability to stain a variety of cellular components, and strong sensitivity of its fluorescence properties to its dielectric environment.

The potent effect of mycolactone on lipid membranes

Mycolactone is a lipid-like endotoxin synthesized by an environmental human pathogen, Mycobacterium ulcerans, the causal agent of Buruli ulcer disease. Mycolactone has pleiotropic effects on fundamental cellular processes (cell adhesion, cell death and inflammation). Various cellular targets of mycolactone have been identified and a literature survey revealed that most of these targets are membrane receptors residing in ordered plasma membrane nanodomains, within which their functionalities can be modulated. We investigated the capacity of mycolactone to interact with membranes, to evaluate its effects on membrane lipid organization following its diffusion across the cell membrane. We used Langmuir monolayers as a cell membrane model. Experiments were carried out with a lipid composition chosen to be as similar as possible to that of the plasma membrane. Mycolactone, which has surfactant properties, with an apparent saturation concentration of 1 μM, interacted with the membrane at very low concentrations (60 nM). The interaction of mycolactone with the membrane was mediated by the presence of cholesterol and, like detergents, mycolactone reshaped the membrane. In its monomeric form, this toxin modifies lipid segregation in the monolayer, strongly affecting the formation of ordered microdomains. These findings suggest that mycolactone disturbs lipid organization in the biological membranes it crosses, with potential effects on cell functions and signaling pathways. Microdomain remodeling may therefore underlie molecular events, accounting for the ability of mycolactone to attack multiple targets and providing new insight into a single unifying mechanism underlying the pleiotropic effects of this molecule. This membrane remodeling may act in synergy with the other known effects of mycolactone on its intracellular targets, potentiating these effects.

Spectroscopic studies of the mechanism of reversible photodegradation of 1-substituted aminoanthraquinone-doped polymers

The mechanism of reversible photodegradation of 1-substituted aminoanthraquinones doped into poly(methyl methacrylate) and polystyrene is investigated. Time-dependent density functional theory is employed to predict the transition energies and corresponding oscillator strengths of the proposed reversibly and irreversibly damaged dye species. Ultraviolet-visible and Fourier transform infrared (FTIR) spectroscopy are used to characterize which species are present. FTIR spectroscopy indicates that both dye and polymer undergo reversible photodegradation when irradiated with a visible laser. These findings suggest that photodegradation of 1-substituted aminoanthraquinones doped in polymers originates from interactions between dyes and photoinduced thermally degraded polymers, and the metastable product may recover or further degrade irreversibly.

A Fluorescent Polymer Probe with High Selectivity toward Vascular Endothelial Cells for and beyond Noninvasive Two-Photon Intravital Imaging of Brain Vasculature

A chromophore-engineering strategy that relies on the introduction of a ground-state distortion in a quadrupolar chromophore was used to obtain a quasi-quadrupolar chromophore with red emission and large two-photon absorption (2PA) cross-section in polar solvents. This molecule was functionalized with water-solubilizing polymer chains. It constitutes not only a remarkable contrast agent for intravital two-photon microscopy of the functional cerebral vasculature in a minimally invasive configuration but presents intriguing endothelial staining ability that makes it a valuable probe for premortem histological staining.

Imaging of living cells and zebrafish in vivo using a ratiometric fluorescent probe for hydrogen sulfide

We have developed a novel colorimetric and ratiometric fluorescence probe for the selective and sensitive monitoring of hydrogen sulfide based on a dicyanoisophorone platform. An excellent linear relationship of fluorescence intensity ratio (I637/I558) (R(2) = 0.9867) versus hydrogen sulfide concentration in the range of 1-12 μM was obtained. This probe exhibited a remarkable fluorescence response to hydrogen sulfide over other physiological thiols or biological species, which fluoresces in the red region with a large Stokes shift (172 nm). This probe was successfully utilized to monitor H2S under in vitro physiological conditions and for imaging H2S in living cells and living zebrafish in vivo.

Blue fluorogenic probes for cell plasma membranes fill the gap in multicolour imaging

Newly synthesized blue membrane probes, due to high brightness, large Stokes shift and fluorogenic response, overcome the problem of cell auto-fluorescence and enable multicolor cellular imaging with common green and red markers.