Shiguo Sun

A New Fluorescent Chemodosimeter for Hg2+: Selectivity, Sensitivity, and Resistance to Cys and GSH

On the basis of the mechanism of Hg(2+)-promoted hydrolysis, a new fluorescent chemodosimeter (Rho-Hg1) is reported for single-selective and parts per billion level-sensitive detection of Hg(2+) in natural waters. Moreover, the fluorescence response of Rho-Hg1 to Hg(2+) has little interference from sulfur compounds such as cysteine and glutathione and could be used in the Hg(2+) imaging in living cells.

Fluorescence Ratiometry and Fluorescence Lifetime Imaging: Using a Single Molecular Sensor for Dual Mode Imaging of Cellular Viscosity

Intracellular viscosity strongly influences transportation of mass and signal, interactions between the biomacromolecules, and diffusion of reactive metabolites in live cells. Fluorescent molecular rotors are recently developed reagents used to determine the viscosity in solutions or biological fluid. Due to the complexity of live cells, it is important to carry out the viscosity determinations in multimode for high reliability and accuracy. The first molecular rotor (RY3) capable of dual mode fluorescence imaging (ratiometry imaging and fluorescence lifetime imaging) of intracellular viscosity is reported. RY3 is a pentamethine cyanine dye substituted at the central (meso-) position with an aldehyde group (CHO). In nonviscous media, rotation of the CHO group gives rise to internal conversion by a nonradiative process. The restraining of rotation in viscous or low-temperature media results in strong fluorescence (6-fold increase) and lengthens the fluorescence lifetime (from 200 to 1450 ps). The specially designed molecular sensor has two absorption maxima (λ(abs) 400 and 613 nm in ethanol) and two emission maxima (in blue, λ(em) 456 nm and red, 650 nm in ethanol). However it is only the red emission which is markedly sensitive to viscosity or temperature changes, providing a ratiometric response (12-fold) as well as a large pseudo-Stokes shift (250 nm). A mechanism is proposed, based on quantum chemical calculations and (1)H NMR spectra at low-temperature. Inside cells the viscosity changes, showing some regional differences, can be clearly observed by both ratiometry imaging and fluorescence lifetime imaging (FLIM). Although living cells are complex the correlation observed between the two imaging procedures offers the possibility of previously unavailable reliability and accuracy when determining intracellular viscosity.

An ICT-based ratiometric probe for hydrazine and its application in live cells

Hydrazine is an important industrial chemical but also very toxic thus requiring rapid detection agents. A ratiometric fluorescence probe that enables rapid, low-limit and naked-eye detection is successfully designed and used for hydrazine determination in live cells.

A Ratiometric Near-Infrared Fluorescent Probe for Hydrazine and Its in Vivo Applications

Based on modulation of the conjugated polymethine π-electron system of a cyanine dye derivative, a ratiometric near-infared fluorescent probe (Cy7A) for hydrazine (N2H4) has been designed and synthesized. Cy7A can be selectively hydrazinolysized with great changes in its fluorescent excitation/emission profiles, which makes it possible to detect N2H4 in water samples and living cells and, for the first time, visualize N2H4 in living mice.

A Fluorescent Ratiometric Chemodosimeter for Cu2+ Based on TBET and Its Application in Living Cells

Based on a through bond energy transfer (TBET) between Rhodamine and a naphthalimide fluorophore, a fluorescent ratiometric chemodosimeter RN1 was designed and prepared for single selective detection of Cu(2+) in aqueous solution and in living cells, as Cu(2+) acts as not only a selective recognizing guest but also a hydrolytic promoter.

Fluorescent Probes for Pd2+ Detection by Allylidene–Hydrazone Ligands with Excellent Selectivity and Large Fluorescence Enhancement

Because palladium is widely used in various catalysts and converters, which results in a high level of contamination of water systems and the soil by residual palladium, there is an urgent need for Pd(2+)-sensitive and -selective probes. Based on the special affinity of Pd(2+) to conjugated double-bond ligands, two fluorescence probes (RPd2 and RPd3) that contain conjugated allylidene-hydrazone ligands that link to colorless rhodamine-spirolactam have been developed. The results show that conjugated allylidene-hydrazones have a much better affinity toward Pd(2+), and consequently provide the probes with more acute color change and fluorescence enhancement (≈170-fold), and better selectivity over other metal ions (especially platinum-group elements, or PGEs) than the unconjugated allyl-hydrazine. With richer electron density and a more suitable stereo effect in the allylidene-hydrazone group, RPd2 displays the best specificity toward Pd(2+) and affords convenient detection by the naked eye. Its potential application for Pd(2+)-contaminated water and soil-sample analysis is revealed by proof-of-concept experiments.

Naphthylamine-rhodamine-based ratiometric fluorescent probe for the determination of Pd2+ ions.

A naphthylamine-rhodamine hybrid ratiometric and colorimetric fluorescent probe (RN) was designed and synthesized. RN can identify Pd(2+) ions with high selectivity and sensitivity. Furthermore, the probe can be used to monitor Pd(2+) ions in live mice by fluorescence imaging.

Carboxyl BODIPY Dyes from Bicarboxylic Anhydrides: One-Pot Preparation, Spectral Properties, Photostability, and Biolabeling

New fluorescent dyes based on 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) and functionalized with a free carboxyl group have been conveniently synthesized from pyrroles and dicarboxylic anhydrides in one-pot reactions. Their spectral properties in different solvents showed little effect of solvatochromism (<10 nm). The methyl groups on the BODIPY skeleton benefit the fluorescence quantum yields (Phi(f) up to 0.80 in water) but affect the photostability of the dyes. Photooxidation and photodegradation experiments suggest that dyes 1a and 2a exhibit excellent photostability, especially in water, and several factors were taken into account to elucidate the experimental phenomena. Dyes 1c and 2c, derived from 1a and 2a via the esterification of NHS (N-hydroxysuccinimidyl ester), can be easily acquired in high yields (>90%). Single crystal X-ray structures of dyes 2c and 3a are also obtained and discussed. The fluorescence labeling of BSA and followed prestaining method for gel electrophoresis of BSA demonstrate that the protein can be directly observed by naked eyes at as low as 2 ng level under a normal UV fluorescence electrophorogram gel image system.

An Effective Minor Groove Binder as a Red Fluorescent Marker for Live‐Cell DNA Imaging and Quantification

Since the understanding of DNA organization and structure in vivo is so important, fluorescent staining techniques using organic DNA-binding molecules are required for biological research and medical diagnosis, including cellular imaging and DNA quantification. However, membrane-permeable DNA-specific stains are uncommon. The minor groove binders 4’,6-diamidino-2-phenylindole (DAPI) and Hoechst 33258 are presently used for DNA-specific staining, but they require ultraviolet excitation, which can lead to cellular damage due to lengthy irradiation. SYTO stains do provide cell-permeable dyes excitable by visible and near-infrared radiation. Unfortunately they are not specific nuclear stains, and moreover are of undisclosed chemical structures. Although the cell-permeant anthraquinone dye DRAQ5 shows red fluorescence emission and DNA-specific labeling, it is a DNA intercalator, which seriously interferes with the structure and function of nuclear DNA, in contrast to the minor groove binders such as SYTO17. Therefore, a pressing need exists to develop fluorescent dyes satisfying the multiple criteria of long-wavelength excitation/emission, high DNA selectivity, and live-cell permeability. Recently, a terbium complex [Tb·L] [2] was described which stained the nuclear DNA in mitotic cells using very low dye concentrations (< 1 mm). Unfortunately, intense irradiation of 350 nm is needed as excitation light. BENA435, with an N,N-dimethylpropane-1,3-diamine group, was reported to stain the nucleus in live cells, but still with excitation/emission located at the cyan region (lex(DNA) = 435 nm; lem(DNA) = 485 nm). Chang et al. [4] have discovered an excellent DNA-selective probe, C61, with relatively long emission wavelength (lem(DNA) = 540 nm) for live-cell nuclear imaging and DNA quantification. C61 shows a 19.9-fold fluorescence increase when bound to doublestranded (ds) DNA (FF DNA = 0.0675). Another promising finding has been reported by Thomas et al. , namely that a dinuclear ruthenium(II) polypyridyl complex (lem(DNA) = 680 nm) can be used as a nuclear DNA stain for both luminescence and transmission electron microscopy. Despite the high hydrophilicity and charge of the molecule, it was still taken up by live cells, but only if a relatively high concentration of more than 200 mm was used. In fluorescence microscopic imaging studies, it is desirable for DNA staining to involve large fluorescence enhancements, and for nuclei to stain rapidly even when low concentrations of dye are used, as this minimizes dye toxicity to live cells. Herein, we report a novel red fluorescent dye DEAB-TO3 (Scheme 1, DEAB = (diethylamino)butyl)), a TO-3 analogue with long-wavelength excitation and emission

Aggregation Control of Squaraines and Their Use as Near-Infrared Fluorescent Sensors for Protein

A series of squaraine dyes are found to be in H- or J-aggregates and are almost nonfluorescent in aqueous solution. Upon addition of bovine serum albumin (BSA), however, the fluorescence intensity (at lambda(em) approximately 690 nm) increases by a factor of up to 200. Transformation of the dye molecules from the aggregates to the monomeric species appears to be responsible for the large fluorescence turn-on. While both H- and J-aggregates contribute to the observed fluorescence turn-on, the former appears to play a more important role. Electrophoresis imaging shows that these probes are good BSA indicators.