Shukun Xu

Polyethyleneimine modified fluorescent carbon dots and their application in cell labeling.

Fluorescent carbon dots (CDs) were solvothermaly synthesized in water-glycol medium by using glucose as carbon source and then modified with polyethyleneimine (PEI) for the first time to improve fluorescence quality. The as-prepared CDs were monodispersed sphere particles with a diameter of about 7.5 nm, emitting strong fluorescence which is excitation wavelength-dependent, with a quantum yield of 3.5%. After PEI modification, there was a 300-fold enhancement in fluorescence intensity and also a red shift in emission wavelength. The as-prepared CDs were then conjugated with CEA8 antibody to label and image HeLa cells in vitro. We also tested the cytotoxicity of these CDs using HeLa cells. No apparent cytotoxicity was observed, demonstrating much better biosafety property compared with CdTe quantum dots.

Hydrothermal synthesis of GSH-TGA co-capped CdTe quantum dots and their application in labeling colorectal cancer cells.

We have successfully synthesized GSH and TGA co-capped CdTe quantum dots (QDs) with good biological compatibility and high fluorescence intensity. The effects of different reaction time, temperature, pH value, ligand concentration and the molar ratio of GSH/TGA were carefully investigated to optimize the synthesis condition. The optical properties of as-prepared CdTe QDs were studied by UV-visible absorption spectrum and fluorescence spectrum, meanwhile their structure and morphology were characterized using transmission electron microscope (TEM), Fourier transform infrared spectra (FT-IR) and X-ray powder diffraction (XRD). Compared with the CdTe QDs that are single-capped with either GSH or TGA, the GSH-TGA co-capped CdTe QDs demonstrated significantly improved fluorescence intensity and optical stability. In addition, GSH-TGA co-capped CdTe QDs were conjugated to amonoclonal antibody ND-1. The GSH-TGA co-capped CdTe QDs-antibody probe was successfully used to label colorectal cancer cells, CCL187, in vitro.

Determination of ascorbic acid via luminescence quenching of LaF3:Ce,Tb nanoparticles synthesized through a microwave-assisted solvothermal method

A novel approach for the rapid determination of ascorbic acid was developed based on the direct luminescence quenching of LaF3:Ce,Tb nanoparticles. The LaF3:Ce,Tb nanoparticles were synthesized via a microwave-assisted method with ionic liquids (BmimBF4) as the fluorine source. The as-prepared nanoparticles were uniformly ellipsoidal with an average size of about 12 nm. They are water soluble and highly fluorescent under 249 nm excitation. A new method for the rapid determination of ascorbic acid was established based on the large degree of overlap between the excitation spectrum of LaF3:Ce,Tb nanoparticles and the absorption spectrum of ascorbic acid. Ascorbic acid exhibits a broad band from 200 to 300 nm with the maximum absorption at 260 nm, which can absorb the excitation light of LaF3:Ce,Tb nanoparticles, consequently resulting in the luminescence quenching. The results showed a good inverse linear relationship between the luminescent intensity of LaF3:Ce,Tb nanoparticles and the concentration of ascorbic acid in the range 8.0 × 10−6 to 1.0 × 10−4 mol L−1 (R = 0.9995), with the detection limit of 2.4 × 10−6 mol L−1 and a RSD of 0.5% (5.33 × 10−5 mol L−1, n = 11). Compared with the standard redox titration method, our new method is effective for the determination of ascorbic acid.

L‐Cysteine capped CdTe–CdS core–shell quantum dots: preparation, characterization and immuno‐labeling of HeLa cells

Functionalized CdTe-CdS core-shell quantum dots (QDs) were synthesized in aqueous solution via water-bathing combined hydrothermal method using L-cysteine (L-Cys) as a stabilizer. This method possesses both the advantages of water-bathing and hydrothermal methods for preparing high-quality QDs with markedly reduced synthesis time, and better stability than a lone hydrothermal method. The QDs were characterized by transmission electronic microscopy and powder X-ray diffraction and X-ray photoelectron spectroscopy. The CdTe-CdS QDs with core-shell structure showed both enhanced fluorescence and better photo stability than nude CdTe QDs. After conjugating with antibody rabbit anti-CEACAM8 (CD67), the as-prepared l-Cys capped CdTe-CdS QDs were successfully used as fluorescent probes for the direct immuno-labeling and imaging of HeLa cells. It was indicated that this kind of QD would have application potential in bio-labeling and cell imaging.

Direct and indirect immunolabelling of HeLa cells with quantum dots.

With excellent optical properties, quantum dots (QDs) have been made as attractive molecular probes for labelling cells in biological research. In this study high-quality CdSe QDs prepared in a paraffin-oleic acid system were used as fluorescent labels in direct and indirect detection of carcinoembryonic antigen (CEA), a cancer marker expressed on the surface of HeLa cells. The primary antibody (Ab) (rabbit anti-CEA8) and secondary Ab (goat anti-rabbit IgG) were covalently linked to carboxyl-functioned CdSe QDs, and both the QDs-antibody and QDs-IgG probes were successfully used to label HeLa cells. The present study demonstrates the practicability of CdSe QDs as an attractive type of fluorescent labels for biological applications such as protein probes and cell imaging.

Direct Aqueous Synthesis of Cysteamine-Stabilized CdTe Quantum Dots and Its Deoxyribonucleic Acid Bioconjugates

Abstract Cysteamine-stabilized CdTe nanocrystals were prepared by direct aqueous synthesis method. Absorption and fluorescence spectra showed that the as-prepared CdTe quantum dots had good optical properties. The structure and diameter were characterized by transmission electron microscopy (TEM). Cysteamine-capped CdTe nanocrystals showed some particular advantages: excited cysteamine-capped CdTe precursor emits luminescence without heating and emits strong luminescence after heating for 20 min at 100°C. However, other thiol-stabilized CdTe precursors do not emit luminescence without heating. The free amino functional group of the cysteamine-stabilized CdTe nanocrystals directly conjugates with DNA. The conjugates showed a redshift of 19 nm for the maximum emission position and an enhancement of fluorescence intensity of CdTe nanocrystals.

Intense visible multicolored luminescence from lanthanide ion-pair codoped NaGdF4 nanocrystals

Lanthanide ion-pair (Eu(3+)/Tb(3+), Dy(3+)/Tb(3+), Sm(3+)/Tb(3+) and Eu(3+)/Dy(3+)) codoped NaGdF(4) nanocrystals using Ce(3+) as the sensitizer were prepared via the polyol method. The nanocrystals with different codoped lanthanide ion-pairs retain their individual optical properties and the combined spectra can be detected using single-wavelength excitation at about 251 nm. The combined spectra intensity ratios can be adjusted through control of the doping ions molar ratios. Excited with a UV lamp at 254 nm, the as-prepared nanocrystals in aqueous solution emit intense visible emissions of different colors. The nanocrystals were coated with SiO(2), to make them biocompatible.

Labeling of BSA and imaging of mouse T‐lymphocyte as well as mouse spleen tissue by l‐glutathione capped CdTe quantum dots

L-glutathione capped highly fluorescent CdTe quantum dots (QDs) were prepared by an aqueous approach and used as fluorescent labels to link albumin bovine serum (BSA) and rat anti-mouse CD4, which was expressed on mouse T-lymphocyte and mouse spleen tissue. The sharp and narrow emission peaks showed that the as-prepared QDs have desirable dispersibility, uniformity and good fluorescence properties. Both CdTe-BSA and CdTe-CD4 conjugates showed an enhancement of fluorescence intensity over that of bare CdTe QDs. The experimental result of gel electrophoresis confirmed the successful conjugation of CdTe-BSA and CdTe-CD4. The fluorescent microscopic images of CdTe-CD4 labeled mouse T-lymphocyte cells and mouse spleen tissue were compared with that obtained from fluorescein isothiocyanate labeling. It was demonstrated that the CdTe QDs-based probe exhibited much better photostability and fluorescence intensity than fluorescein isothiocyanate, showing a good application potential in the immuno-labeling of cells and tissues.

Study on the sonodynamic activity and mechanism of promethazine hydrochloride by multi-spectroscopic techniques.

In this paper, the bovine serum albumin (BSA) was selected as a target molecule, the sonodynamic damage to protein in the presence of promethazine hydrochloride (PMT) and its mechanism were studied by the means of absorption, fluorescence and circular dichroism (CD) spectra. The results of hyperchromic effect of absorption spectra and quenching of intrinsic fluorescence spectra indicate that the ultrasound-induced BSA molecules damage is enhanced by PMT. The damage degree of BSA molecules increases with the increase of ultrasonic irradiation time and PMT concentration. The results of synchronous fluorescence, three-dimensional fluorescence and CD spectra confirmed that the synergistic effects of ultrasound and PMT induced the damage of BSA molecules. The results of oxidation-extraction photometry with several reactive oxygen species (ROS) scavengers indicate that the damage of BSA molecules could be mainly due to the generation of ROS and both (1)O(2) and OH are the important mediators of the ultrasound-induced BSA molecules damage in the presence of PMT.

Conjugations between Cysteamine-Stabilized CdTe Quantum Dots and Single Stranded DNA

Abstract Cysteamine-stabilized CdTe quantum dots were used to directly conjugate with single stranded DNA through electrostatic attraction between positive amino function groups on the surface of CdTe quantum dots and negatively charged DNA. The conjugates exhibited different optical properties from that of CdTe quantum dots, for example, the fluorescence intensity was enhanced obviously with maximum emission peaks gradually red-shifting, and the conjugates were more stable. Under the optimum conditions, the fluorescence intensity was proportional to concentration of DNA over the range 0.16–0.48 µg/mL. This proposed method demonstrated a versatile tool for the fluorescence probing of target DNA and fluorescence labeling.