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A simple and rapid approach to synthesize monodisperse and biocompatible gold nanoparticles (AuNPs) employing dextran as a reducing and stabilizing agents at different reaction conditions was described. The obtained dextran-gold nanoparticles (Dex-AuNPs) were characterized by transmission electron microscopy (TEM), UV-Vis spectroscopy, Nuclear magnetic resonance (NMR) spectroscopy, Fourier transformer infrared (FTIR) spectroscopy and X-ray diffraction (XRD) analysis. The TEM examinations showed the resultant particles were 4-50 nm in size, monodispersity and uniform particle size distribution. Moreover, the size of the nanoparticles can be controlled by varying the concentration of the reactants. UV-Vis spectra showed that the characteristic localized surface plasmon resonance (LSPR) band of AuNPs was at about 525 nm. NMR spectroscopy and FTIR spectroscopic analysis suggested the detailed structural information of dextran before and after synthesis of AuNPs. XRD and selected area electron diffraction (SAED) pattern analysis demonstrated that the colloidal nanoparticles had a well crystallized structure. The experimental analyses revealed that NaOH played an important role in the synthesis of Dex-AuNPs. And the possible formation mechanism of the fabrication of these Dex-AuNPs was also proposed. MTT assay was utilized to evaluate the cytotoxicity of the synthesized Dex-AuNPs on HeLa cells and SiHa cells. These results suggested that the prepared Dex-AuNPs complexes had excellent biocompatibility and acted as a candidate for further biomedical application.

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Gold nanoparticles (AuNPs) have been researched extensively, such as applied in various biosensors, biomedical imaging and diagnosis, catalysis and physico-chemical analysis. These applications usually required to know the nanoparticle size or concentration. Researchers have been studying a simply and quick way to estimate the concentration or size of nanoparticles from their optical spectra and SPR feature for several years. The extinction cross-sections and the molar attenuation coefficient were one of the key parameters. In this study, we calculated the extinction cross-sections and molar attenuation coefficient (decadic molar extinction coefficient) of small gold nanoparticles by dipole approximation method and modified Beer-Lambert law. The theoretical result showed that the surface plasmon resonance peak of small gold nanoparticles was blueshift with an increase size. Moreover, small AuNPs (sub-10nm) were prepared by using of dextran or trisodium citrate as reducing agent and capping agent. The experimental synthesized AuNPs was also shows a blueshift as increasing particle size in a certain range. And the concentration of AuNPs was calculated based on the obtained molar attenuation coefficient. For small nanoparticles, the size of nanoparticles and surface plasmon resonance property was not showed a positive correlation compared to larger nanoparticles. These results suggested that SPR peak depended not only on the nanoparticle size and shape but also on the nanoparticles environment.

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Alkaline silver colloid with better stability and uniformity was obtained by adding appropriate amount of NaOH to synthesis reaction. The performance of the Ag colloid as surface enhanced Raman scattering (SERS) active substrate was evaluated by methylene blue as the probe molecules and achieved well Raman spectra. The concentration of methylene blue had no effect on the adsorptive behavior of methylene blue on alkaline silver colloid surface in comparison with normal silver colloid. The basic reason for this phenomenon is preferential adsorption of alkaline silver colloid for sulfur atoms of methylene blue so as to increase the intensity of 451 cm-1 Raman peak consistently. The amounts of methylene blue added to alkaline Ag colloid and time-evolution of Raman spectra were also investigated. Additionally, the alkaline silver colloid was prepared to be silver spot and applied to detect melamine doped milk. The relationship of the doping amount of melamine and the Raman signal intensity was obtained. The linearity relationship in the concentration range between 3 and 60 mg.L-1 with detect limit 0.28 mg.L-1 was achieved based on the intensity of 691 cm-1 Raman peak This method required only 5 microL sample size and 5 s for detection and suggested that this presented method with its advantages of speediness, briefness and lower cost has a good application foreground.

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Cetyltrimethyl ammonium bromide (CTAB) has been extensively applied in the solution-phase synthesis of many types of colloidal nanoparticles. However, the uses of CTAB were mainly considered as template or capping agents to form controllable shape and protect the product from agglomeration. Here it was discovered that CATB could serve as a very mild reductant to reduce gold salt precursors preparing gold nanoparticles (GNPs) at base environment. CTAB acted as the reducing agent suffering a partial degradation and forming CTA macro radicals. FTIR proved the formation of CCl and/or CBr bond after CTAB degraded. The characterization of synthesized GNPs was examined by UV-Vis spectra, TEM and XRD. Several factors affecting the process of reaction, such as the amount of NaOH, the molar ratio of CTAB and HAuCl(4), the reaction temperature, the effect of light and oxygen, and stirring were discussed.

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Green-emitting LaF3:Ce, Tb phosphor nanoparticles were synthesized by a simple hydrothermal method and characterized by XRD, TEM and fluorescence spectra. The prepared samples had a hexagonal shape, fine size (30 nm), and high brightness under ultraviolet, and the structure of LaF3 remained unchanged after being doped with Ce3+ and Tb3+ ions. The blue Ce3+ emission centered at 261 nm is efficiently quenched in the samples of LaF3:Ce, Tb, in which the dominant emission is in the green at 544 nm, originating from the doped Tb3+ ions' transition of (5)D4 to (7)F5. Excitation spectra of the LaF3:Ce, Tb, observed at 544 nm, consist of both contributions from Ce3+ and Tb3+ ions. There is energy transfer of Ce3+ --> Tb3+ in this system. The energy transfer mechanism was discussed. Above all, the phosphor nanoparticles have high photoluminescence intensity even without any calcination, about twice that of bulk materials prepared by high temperature solid synthesis, and the intensity is also stronger than calcined phosphor nanoparticles.

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LaF3:Eu3+ nanoparticles were prepared by a simple hydrothermal process at low temperature and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and fluorescence spectrum. Well-dispersed nanoparticles with an average size of 30 nm and a hexagonal shape were obtained. The influences of reaction temperature and time on the preparation and luminescence of LaF3:Eu3+ nanoparticles were investigated. Luminescent quenching occurred at a much higher concentration ( approximately 25mol%) and stronger luminescent intensity than in bulk LaF3:Eu3+. Fluorescence intensity of the LaF3:Eu3+ nanoparticles varied remarkably with calcination temperatures. It was found that samples without any further calcinations can emit quite strong fluorescence.

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