Haitao Xu

Synthesis and properties of fluorescence dyes: tetracyclic pyrazolo[3,4-b]pyridine-based coumarin chromophores with intramolecular charge transfer character.

Two series of new tetracyclic pyrazolo[3,4-b]pyridine-based coumarin chromophores were synthesized through a facile reaction between 3-aldehyde-7-diethylaminocoumarin (5) or 3-acetyl-7-diethylaminocoumarin (6) and 5-aminopyrazole derivatives (7) in a one-pot procedure. Different condensed products were obtained from compounds 5 and 6, and the potential reaction mechanism was studied using the reaction of 5 with 5-amino-1-phenylpyrazole (7a). The molecular structures were characterized by NMR and HRMS and confirmed by X-ray diffraction. The photophysical, electrochemical, and thermal properties of these compounds were investigated by absorption spectroscopy, fluorescence spectroscopy, single photon counting technique, cyclic voltammetry, thermogravimetric analysis, etc. Results show that the compounds exhibited high fluorescence quantum yields and good electrochemical, thermal, and photochemical stabilities. In addition, the application of these highly fluorescent compounds in living cell imaging was also explored by laser scanning confocal microscopy.

Reversible "off-on" fluorescent chemosensor for Hg2+ based on rhodamine derivative.

A novel and simple fluorescent chemosensor based on rhodamine was designed and synthesized to detect Hg(2+) with high selectivity. The structure of chemosensor 1 was characterized by IR, (1)H NMR, and HRMS spectroscopies. Chemosensor 1 exhibited distinct fluorescent and colorimetric changes toward Hg(2+) in an ethanol/water (80/20, v/v) solution, which resulted in the formation of 1/Hg(2+) complex with the Hg(2+)-induced ring opening of the spirolactam ring in rhodamine. The reversibility of chemosensor 1 was verified through its spectral response toward Hg(2+) ions and TBAI (tetrabutylammonium iodide) titration experiments.

Silicon Nanowire-Based Fluorescent Nanosensor for Complexed Cu2+ and its Bioapplications

A silicon nanowires (SiNWs)-based fluorescent sensor for complexed Cu(2+) was realized. High sensitivity and selectivity of the present sensor facilitate its bioapplications. The sensor was successfully used to detect the Cu(2+) in liver extract. Meanwhile, real-time and in situ monitoring of Cu(2+) released from apoptotic HeLa cell was performed using the as-prepared SiNW arrays-based sensor. These results indicate that the present SiNWs-based sensor would be of potential applications in revealing the physiological and pathological roles of Cu(2+).

Imaging of nucleolar RNA in living cells using a highly photostable deep-red fluorescent probe.

A new crescent-shape fluorescent probe (named here as CP) that selectively stains RNA in nucleoli of living cells is prepared. CP shows a deep-red emission (658 nm) and a large Stokes shift because of the introduction of rigid-conjugated coumarin moiety into the molecular structure. Cell imaging experiments indicate that CP can rapidly stain nucleoli in living cells by binding with nucleolar RNA, showing performance superior to commercially available nucleoli dye SYTO RNASelect in terms of high photostability and selectivity. More significantly, these excellent properties together with low cytotoxicity enable CP to monitor nucleolar RNA changes during mitosis, and after treating with anti-cancer drugs cisplatin, actinomycin D and α-amanitin. Thus, CP could be a potential tool for real-time, long-term visualization of the dynamic changes for nucleolar RNA and evaluation of the therapeutic effect for anti-cancer drugs that targeted RNA polymerase I (Pol I).

Aminobenzofuran-Fused Rhodamine Dyes with Deep-Red to Near-Infrared Emission for Biological Applications

Aminobenzofuran-fused rhodamine dyes (AFR dyes) containing an amino group were constructed by an efficient condensation based on 3-coumaranone derivatives. AFR dyes exhibited significantly improved properties, including deep-red and near-infrared emissions, a large Stokes shift, good photostability, and wide pH stability. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium assay experiments show that these AFR dyes are biocompatible for their low cytotoxicity to both A549 and HeLa cells. Cell imaging data reveal that AFR1, AFR1E, and AFR2 are mainly located in the mitochondria, while AFR3 is a lysosome tracker. As far as we know, NIR AFR3 is the longest fluorescent rhodamine derivative containing the amino group. These amino group-containing AFR dyes hold great potential in fluorogenic detection, biomolecule labeling, and cell imaging.

Deep-Red Emissive Crescent-Shaped Fluorescent Dyes: Substituent Effect on Live Cell Imaging

A series of crescent-shaped fluorescent dyes (CP1-CP6) were synthesized by hybridizing coumarin and pyronin moieties with different amino substituents at both ends. The molecular structures and photophysical properties of these fluorescent dyes were investigated through X-ray diffraction, absorption spectroscopy, and fluorescence spectroscopy. Results show that the fluorescent dyes exhibited crescent-shaped structures, deep-red emissions (approximately 650 nm), and significant Stokes shifts. In live-cell-imaging experiments, CP1 stains mitochondria, whereas CP3 and CP6 stain the lysosomes in a cytoplasm and the RNA in nucleoli. The relationships between different amino substituent groups and the imaging properties of CP dyes were discussed as well. Additionally, findings from the cytotoxicity and photostability experiments on living cells indicated the favorable biocompatibility and high photostability of the CP dyes.

Modified silicon nanowires: a fluorescent nitric oxide biosensor with enhanced selectivity and stability

A fluorescence sensor for nitric oxide (NO) was realized by covalently immobilizing reduced fluoresceinamine molecules onto the surface of silicon nanowires (SiNWs). The fluorescence intensity of the sensor can be greatly enhanced by NO. The sensor exhibits excellent selectivity for NO against other reactive species. Facile synthesis, nontoxicity, rapid response and use in a 100% aqueous solution endows the present sensor with suitability for biosystems. As an application, the sensor was used to detect NO released from liver extract, and exhibited high sensitivity and selectivity as well as rapid response. The fluorescence image from a single SiNW-based sensor showed a fine spatial resolution. The present sensor paves a way to detect NO at specific location in a single cell by inserting a single SiNW-based sensor into the cell.

Facile method for modification of the silicon nanowires and its application in fabrication of pH-sensitive chips.

A novel, facile, and effective method for modification of SiNWs or SiNW arrays has been developed. In this method, reaction between reductive Si-H bonds on the surface of SiNWs and the aldehyde group containing in organic molecules has been used for immobilization of organic molecules onto the surface of SiNW arrays. The method is time saving and can be operated at room temperature without any other complex reaction requirement. Fluorescence images, XPS, fluorescence spectra, and IR spectra were used for characterization of the modification. Through this method, a SiNW array-based pH sensitive chip was realized by covalently immobilizing 5-aminofluorescein molecules onto the surface of SiNW arrays with glutaraldehyde as linker molecules. Fluorescence intensity of the chip increased with increasing of pH value and a linear relationship between fluorescence intensity and pH values was acquired. In addition, the chip has been successfully used for real-time and in situ monitoring of extracellular pH changes for live HeLa cells and the result exhibited fine resolution of time and space.

Highly portable fluorescent turn-on sensor for sulfide anions based on silicon nanowires

By covalently modifying 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane (ligand) and 4-amino-1,8-naphthalic anhydride (fluorophore) onto the surface of silicon nanowires (SiNWs) and subsequently complexing them with copper ions (Cu2+), a SiNWs-based fluorescent sensor for sulfide anions (S2−) was realized. Based on such a ligand/Cu2+ approach, the new type of sensor realizes rapid sensing of S2−, and exhibits high sensitivity and selectivity for S2− in water. Moreover, the as-prepared SiNW arrays-based sensor was successfully used in real time and in-situ monitoring of S2− in running water by directly inserting it into the water. The present SiNW arrays-based sensor can be developed into a portable commercial device applied in environmental analysis after further optimizing the technique and finely quantifying the response of the sensor.