Depu Chen

Synthesis and characterization of multi-functional nanoparticles possessing magnetic, up-conversion fluorescence and bio-affinity properties

Multi-functional nanoparticles possessing magnetic, up-conversion fluorescence and bio-affinity properties were synthesized and characterized. The particles have a core/shell structure. Iron oxide nanoparticles of 5–15 nm diameter were synthesized as the magnetic core. The core was covered with ytterbium and erbium co-doped sodium yttrium fluoride (NaYF4:Yb,Er), an efficient infrared-to-visible up-conversion phosphor. The phosphor shell was prepared by co-precipitation of the rare-earth metal salts with fluoride in the presence of EDTA and the magnetic nanoparticle. After the magnetic/fluorescent hybrid particle was coated with SiO2 and activated with glutaraldehyde, streptavidin was immobilized on the particle. The magnetic/fluorescent nanoparticles were found by transmission electron microscopy to be well-dispersed spherical particles with an average diameter of 68 nm. Both energy dispersive X-ray microanalysis and X-ray fluorescence spectra revealed the existence of iron in the particle. Measurements performed on a vibrating sample magnetometer obtained a strong magnetic response for the particle and fluorescence measurements demonstrated its up-conversion property. X-Ray diffraction analysis suggests the phosphor shell has the same structure as the pure NaYF4:Yb,Er nanoparticles we prepared in a previous study (G. S. Yi, H. C. Lu, S. Y. Zhao, Y. Ge, W. J. Yang, L. H. Guo, D. P. Chen and J. Cheng, submitted). Streptavidin-coated magnetic/fluorescent particles were found to bind specifically to a glass slide spotted with biotinylated IgG and emit up-conversion fluorescence, confirming the successful coating of the protein and retention of its optical activity and bio-affinity.

Monodisperse, size-tunable and highly efficient β-NaYF4:Yb,Er(Tm) up-conversion luminescent nanospheres: controllable synthesis and their surface modifications

Monodisperse, oil-dispersible β-NaYF4:Yb,Er(Tm) up-conversion (UC) luminescent nanospheres (NPs) have been successfully synthesized. The as-prepared NPs show high size-uniformity without any size-selection process, and the sizes of the NPs can be tuned in the range of 18 nm–45 nm, which are well suitable for biolabels. The NPs are thoroughly characterized and a growth mechanism is proposed. By co-doping Yb-Er or Yb-Tm, the as-prepared NPs can show bright green or blue UC luminescence under the irradiation of a 980 nm near-infrared (NIR) laser, and the UC luminescence can be obviously enhanced by constructing a NaYF4:Yb,Er@NaYF4 core/shell structure. Furthermore, the hydrophobic UC nanospheres (UCNPs) are converted into water-soluble by a robust ligand-exchange pathway with poly(acrylic acid). The presence of free carboxylic acid groups on their surfaces not only results in high solubility in water, but also allows further conjugation with biomolecules such as antigens, antibodies and oligonucleotides, which pave the way for potential bio-applications of the UCNPs.

Microminiaturized immunoassays using quantum dots as fluorescent label by laser confocal scanning fluorescence detection.

An immunoassay readout method based on fluorescent imaging analysis with laser confocal scanning is described. The ZnS-coated CdSe quantum dots (ZnS/CdSe QDs) were linked to a detection antibody. Immunoassay was carried out on a glass chip using a sandwich assay approach, where antibody covalently bound to a glass chip was allowed to capture antigen specially. Afterwards, the detection antibody labeled with QD was allowed to bind selectively to the captured antigen. The fluorescent signals of the sandwich conjugate were detected by a laser confocal scanner. A diode laser was used to excite efficiently the fluorescent signals while bovine serum albumin was used to eliminate nonspecific binding sites. The detection limit of this approach was up to 10(-9) M under current experimental conditions. The specificity of the QDs-labeled immunoglobulin (IgG) was tested by an experiment using goat IgG and human IgG samples. The result was consistent with the binding specificity in a sandwich-type assay. The potential of this method to function as a simple and efficient readout strategy for immunoassay in biochip is discussed.

Morphology- and phase-controlled synthesis of monodisperse lanthanide-doped NaGdF4nanocrystals with multicolor photoluminescence

Monodisperse, regular-shaped and well-crystallized nanocrystals (NCs) of lanthanide-doped NaGdF4 with diverse shapes and structures are synthesized in high boiling organic solvents 1-octadecene and oleic acid, through a competitive nucleation and growth pathway. The NCs can be manipulated to different morphologies and phase structures by using controlled variations in the reaction conditions such as composition of the solvent, temperature or reaction time. The NCs are thoroughly characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), high resolution TEM (HRTEM), field emission scanning electron microscopy (FESEM), IR spectroscopy, and photoluminescence. Possible mechanisms of NC nucleation and growth, size and shape evolution are proposed and tested. With different dopants, the NCs can show intensive multicolor down-conversion emissions under 254 nm UV excitation or up-conversion fluorescence under 980 nm NIR excitation, showing great promise in applications such as multi-analyte biolabels, staining, displays and other optical technologies.

Controlled synthesis of hexagon shaped lanthanide-doped LaF3 nanoplates with multicolor upconversion fluorescence

Yb–Er, Yb–Ho and Yb–Tm co-doped LaF3 IR-to-visible upconversion fluorescent nanocrystals with well-crystallized hexagonal phases were synthesized by a solvothermal technique, which was based on the decomposition of rare-earth trifluoroacetates. During this reaction the generation of fluoride ions and the nucleation of the LaF3 occurred almost simultaneously. Through a phase transition procedure, nanoplates with well-crystallized hexagon shape and an average edge length of 20–30 nm were obtained because the nucleation and growth processes were slow. The size, morphology and phase transition of the rare-earth fluorides were discussed in relation to solvents, reaction time and temperature and a reaction mechanism was proposed. Furthermore, these nanoplates could be easily dispersed in organic solutions and formed a transparent colloidal solution. Under 980 nm IR excitation, multicolor emission bands can be observed for different codopants, which show potential applications as color displays, light-emitting diodes, optical storage, optoelectronics and biolabels.

Synthesis and characterization of strongly fluorescent europium-doped calcium sulfide nanoparticles

Nanometer-sized europium-doped calcium sulfide (CaS–Eu) particles were synthesized for the first time for potential use in bioassays, in particular, in biochip-based analysis. The CaS–Eu nanoparticles were prepared through a wet chemical process in ethanol. The average diameter of the nanoparticles was about 15 nm. They were characterized by UV–Vis spectrometry, scanning electron microscopy, X-ray diffraction, fluorescence spectroscopy and X-ray sequential fluorescence spectroscopy. Both electron paramagnetic resonance measurement and an extensive washing experiment revealed that the dopant atoms were internal ions dispersed throughout the whole CaS–Eu nanoparticles. Factors affecting the fluorescent properties of the nanoparticles were examined. It was found that the emission wavelength of the CaS–Eu nanoparticles could be altered by partial replacement of calcium with other alkaline earth metals such as magnesium, strontium and barium, and this makes the nanoparticles ideal for use as biochips where a multicolor-based bioassay is common.

New tissue engineering material copolymers of derivatives of cellulose and lactide : their synthesis and characterization

This paper reported the grafting copolymerization of l-lactide onto hydroxyethyl cellulose (PLA-HEC) or hydroxypropyl cellulose (PLA-HPC). They were obtained from ring-opening copolymerization of l-lactide with HEC or HPC in different mole ratios at 128°C. Sn(Oct)2 or LiCl was used as catalysts for the polymerization reaction. 400 MHz 1H NMR analysis of products indicated that both Sn(Oct)2 and LiCl could catalyze the reactions. Both PLA-HEC and PLA-HPC were biodegradable polymers with a good bioabsorbability, lack of toxicity, and were suitable for the use as tissue engineering materials.

SOLID SUBSTRATE PHOSPHORESCENT IMMUNOASSAY BASED ON BIOCONJUGATED NANOPARTICLES

Room-temperature phosphorescent (RTP) immunoassay based on dye embedded polyglutaraldehyde nanoparticles was described. Phosphorescent nanoparticles had been covalently linked to antibody to probe specifically antigen. The immunoassay was conducted by the typical procedure of sandwich type assay with polyamide membrane (PAM) sheet as solid substrate. In comparison with single organic dye molecule, the nanoparticle probe was bright, and more stable against photobleaching. Moreover, the solid substrate at room temperature offered high signal and low background, which led to gain rather perfect sensitivity. The concentration of immunoglobulin (IgG) in reaction with nanoparticles was optimized and the dependence of the phosphorescence intensity on the concentration of antigen was studied.

First Principles Investigation of Water Adsorption on Fe (110) Crystal Surface Containing N

Understanding the interaction of water with iron is crucial to explore the nature of subsequent corrosion of iron-based structural materials. However, because of the lack of the comprehensive understanding about the water behavior on iron surfaces, the detailed knowledge about the role of water in corrosion processes is still unclear. In the process of researches of water adsorption on clean iron surfaces, foreign particle of N is easier brought into the system. In this work, in order to explore water chemistry on the surfaces of the iron containing N, water adsorption on N/ Fe (110) based on first principles calculations are comparatively investigated. Geometry structure and electronic structure are calculated using the method of density functional theory. The calculation results reveal that the existence of N atom has not got the significant changes of the geometry structure of Fe (110)/ H2O interface. And the existence of N atom has not significantly affected the interaction of H2O molecule Fe (110) surface.

AN IMPROVED METHOD FOR EFFICIENT AND CONVENIENT SYNTHESIS OF DIOCTANOYL PEROXIDE

ABSTRACT Octanoyl chloride in methylene dichloride was added to the hydrogen peroxide solution containing 5 mol.l−1 NaOH in water-cooled flask, the reaction was carried out with high yields in ten or more minutes under vigorous stirring. The product was characterized by elemental analysis, molecular weight and spectral (IR, 1H NMR) analysis. Furthermore, the method proposed has the advantages of operation at room temperature with safety, reliability and short time consuming.