Arabinogalactan from the Western larch tree: A new, purified and highly water-soluble polysaccharide-based protecting agent for maintaining precious metal nanoparticles in colloidal suspension

TEM and non-contact atomic force microscopy studies conducted on unprotected and protected platinum, palladium and silver nanoparticle suspensions provide evidence for the protective ability of a newly available polysaccharide known as arabinogalactan. The arabinogalactan offers advantages over conventionally used gum arabic in being highly water soluble, capable of being prepared in higher purity and not settling out insoluble material over time. Nanoparticle suspensions prepared in the presence of this protecting agent show a change in overall particle morphology and reduction in the necklace like aggregation typical of unprotected particles on the TEM grids. It is believed that the protective action exerted by the arabinogalactan on the metal nanoparticles arises out of its unique spheroidal structure adopted in aqueous solution which is thought to sequester individual metal particles by virtue of surface interactions between oxide functionalities on the colloid and hydroxyl groups on the arabinogalactan.     

Synthesis of gold nanoparticles using aqueous extract of Calotropis procera latex

This is an account of the use of aqueous extract of the latex of Calotropis procera for the synthesis of gold nanoparticles. UV-Vis spectroscopic studies of the products resulting from reaction between the aqueous latex extract and chlorauric acid indicated the successful synthesis of gold nanoparticles. Reaction parameters viz. concentration of latex extract and reaction time were optimized for maximum yield of gold nanoparticles. Effect of reaction temperature on the synthesis rate of the particles and their optical properties was also studied. Transmission electron microscopic (TEM) studies of the particles revealed the dominance of spherical particles. Mean particle size distribution was found to be 22 ± 10 nm. Crystalline nature of the particles was confirmed from X-ray diffractrograms. FT-IR analysis and protein coagulation test of the gold nanoparticles confirmed capping behaviour of the latex proteins that contributed to their long term stability (6 months) in aqueous medium. Toxicity of the particles was tested on three cell lines, HeLa, A549 and BHK21. The method exploits a cheap and easily available biomaterial not explored so far for the synthesis of metallic nanoparticles.     

Formation of nanocrystalline matrix of sodium rare earth fluoride up-conversion phosphors

Until now, ytterbium and erbium co-doped sodium yttrium fluoride (NaYF4:Yb, Er) is among the most efficient up-conversion phosphors. Its potential for applications in biological and medical fields has interested many scientists. However, the formation mechanism of the co-doped sodium yttrium fluoride nanoparticles is still unknown. Based on the similarity of rare earth elements, this work started with studying the formation mechanism of NaYF4 nanoparticles without doping in aqueous phase. Effects of reactant concentrations, pH, and reaction time on the particle formation were investigated. As the reaction time increased, NaYF4 nanoparticles grew sporadically. Effect of seeding was also studied. The reaction was not accelerated and the particle size was not altered by seeding. The above investigations suggested that in aqueous solution NaYF4 nanoparticles were formed by the aggregation model. The aggregation of the primary particles may play a key role for the formation and size control of the nanoparticles. Smaller particles were achieved by the presence of chelators of Na2-ethylenediaminetetraacetic acid and sodium nitrilotriacetate. This probably resulted from the adsorption of chelators on the NaYF4 nanoparticles and increased the repulsive force between the primary particles, preventing primary particles to form large particles by aggregation.     

Green synthesis of highly stabilized nanocrystalline silver particles by a non-pathogenic and agriculturally important fungus T. asperellum

A controlled and up-scalable biosynthetic route to nanocrystalline silver particles with well-defined morphology using cell-free aqueous filtrate of a non-pathogenic and commercially viable biocontrol agent Trichoderma asperellum is being reported for the first time. A transparent solution of the cell-free filtrate of Trichoderma asperellum containing 1?mM AgNO(3) turns progressively dark brown within 5?d of incubation at 25?°C. The kinetics of the reaction was studied using UV-vis spectroscopy. An intense surface plasmon resonance band at ～410?nm in the UV-vis spectrum clearly reveals the formation of silver nanoparticles. The size of the silver particles using TEM and XRD studies is found to be in the range 13-18?nm. These nanoparticles are found to be highly stable and even after prolonged storage for over 6 months they do not show significant aggregation. A plausible mechanism behind the formation of silver nanoparticles and their stabilization via capping has been investigated using FTIR and surface-enhanced resonance Raman spectroscopy.     

Zinc nanoparticles in solution by laser ablation technique

Colloidal zinc metallic nanoparticles are synthesized using pulsed laser ablation of metal plate in an aqueous solution of suitable surfactant to prevent aggregation. UV-visible absorption, TEM, small angle X-ray diffraction and wide-angle X-ray diffraction are used for the characterization of colloidal zinc metallic nanoparticles. Colloidal nanoparticles are found highly stable for a long time.     

硅烷偶联剂对磁性纳米微球的磁性能影响

以三氯化铁水溶液作原料,采用部分还原沉淀法,控制一些影响反应的参数。制备了纳米磁微粒子,并用硅烷偶联剂进行了表面修饰。利用透射电镜、红外光谱、X射线衍射等手段对磁微粒子的形貌、结构组成、磁化率、磁响应性进行了表征。结果表明所合成的磁微粒子平均粒径为18nm。分布均匀。具有较强的磁响应性。研究还表明偶联剂的加入会影响磁微粒子的磁性能,其加入量有一个适当值,使得改性后的磁微粒子的磁性能最强。     

Preparation and characterization of amphiphilic poly-N-vinylpyrrolidone nanoparticles containing indomethacin

Amphiphilic poly-N-vinylpyrrolidone derivatives (Amph-PVP) with different molecular weight of hydrophilic PVP fragment and one terminal hydrophobic n-alkyl fragment of different length were synthesized for preparation of nano-scaled particles in aqueous media. To estimate novel polymer efficiency and perspective as basis for drug delivery systems, the polymeric micelle-like particles were prepared by dialysis and solvent evaporation methods. Indomethacin was incorporated into hydrophobic inner core of these nanoparticles as a typical model drug. From the dynamic light-scattering measurements, the size of particles formed was less than 200 nm with narrow monodisperse size distribution and nanoparticles size slightly increased with the amount of indomethacin encapsulated into inner core of Amph-PVP particles. The critical aggregation concentration values for prepared polymer samples determined by fluorescence spectroscopy were in micromole range which is lower than it is for common low molecular weight surfactants. As the hydrophobic fragment of amphiphilic polymer increased, the critical aggregation concentration values decreased. An increase of polymer hydrophilic fragment molecular weight produced larger nanoaggregates. In vitro release experiments using indomethacin-loaded Amph-PVP nanoparticles exhibited the sustained release behavior without any burst effect for most polymer samples.     

Tuned optical properties of in-situ synthesized m-nitroaniline doped Ag/PVA nano-composites

Meta-nitroaniline (m-NA) doped silver/poly(vinylalcohol) (Ag/PVA) nanocomposites are prepared via in-situ reduction of silver salt by employing hydrazine hydrate (HH) in order to study the effect of the NLO active m-NA on the optical properties of nanoparticles of silver in the colloidal as well as self supported film form. Reduction of silver salt in aqueous alcoholic PVA with HH is done first followed by doping of the reaction mixture with m-NA. The UV-Visible absorption spectra show peak at about 400 nm for Ag nanoparticles due to surface plasmon resonance phenomenon, which gets blue shifted with the change in m-NA concentration. The Second Harmonic Generation (SHG) studies show improvement in intensity with increasing m-NA concentration up to a saturation point (approximately 2.52 wt% with respect to PVA). Further increase in m-NA concentration leads to decrease in SHG intensity. The solutions and the films are characterized by photoluminescence (PL), FTIR spectroscopy, XRD, SEM, TEM, and thermal analysis. m-NA doped composites showed better PL efficiency. SEM of the nanocomposite film shows uniform distribution of particles within the film. The particle size as shown by TEM is found to be less than 10 nm.     

A facile route to shape controlled CdTe nanoparticles

Hexadecylamine (HDA) capped CdTe nanoparticles have been synthesized using a facile hybrid solution based/thermolysis route. This method involves the reaction by the addition of an aqueous suspension or solution of a cadmium salt (chloride, acetate, nitrate or carbonate) to a freshly prepared NaHTe solution. The isolated CdTe was then dispersed in tri-octylphosphine (TOP) and injected into pre-heated HDA at temperatures of 190, 230 and 270 °C for 2 h. The particle growth and size distribution of the CdTe particles synthesized using cadmium chloride as the cadmium source were monitored using absorption and photoluminescence spectroscopy. The final morphology of the CdTe nanoparticles synthesized from the various cadmium sources was studied by transmission electron microscopy (TEM) and high resolution TEM. The cadmium source has an influence on the final morphology of the particles.     

Synthesis, characterization, and optical properties of AuSe nanoalloys

A solution phase approach to synthesize a new metal-semiconductor nanocomposite, AuSe nanoalloy has been reported. The synthesis has been achieved through UV-photoactivation of preformed Au and Se nanoparticles in micelle. Non-ionic surfactant Triton X-100 was exploited as a micellar medium for effective fusion of gold and selenium particles under UV. Both physical and chemical studies have been performed to characterize the composition and morphology of the particles. UV-visible, TEM, SEM, XPS and AFM analyses were done for characterization purpose. The optical properties of nanocomposites have been substantiated through their interaction with a fluorescent probe, eosin in aqueous solution. The spectroscopic investigation of dye-metal-semiconductor assembly has been examined critically. It has been found that the dye experiences J and H types of aggregation on the surfaces of gold and selenium nanoparticles respectively. Again, the composition dependent change of the emission profile of the probe on different nanocomposite surfaces has been rationalized in accordance with the molecular dimerization of the dye.     

Ni-Fe2O4 nanoparticles as contrast agents for magnetic resonance imaging

Reported herein is the synthesis of a dextran coating on nickel ferrite (Ni-Fe2O4) nanoparticles via chemical coprecipitation. The aqueous solution of the synthesized nanoparticles showed good colloidal stability, and no precipitate was observed 20 months after the synthesis. The coated nanoparticles were found to be cylindrical in shape in the TEM images, and showed a uniform size distribution with an average length and diameter of 17 and 4 nm, respectively. The coated particles were evaluated as potential T1 and T2 contrast agents for MRI. The T1 and T2 relaxations of the hydrogen protons in the water molecules in an aqueous solution of dextran-coated Ni-Fe2O4 nanoparticles were studied. It was found that the T1 relaxivity for the aqueous solution of dextran-coated nanoparticles was slightly greater than that of a commercial Gd-DTPA-BMA contrast agent. The T2 relaxivity, however, was almost twice that of the commercial Gd-DTPA-BMA contrast agent. Animal experimentation also demonstrated that the dextran-coated Ni-Fe2O4 nanoparticles are suitable for use as either T1 or T2 contrast agents in MRI.     

Characterization of silver nanoparticles synthesized on titanium dioxide fine particles

Silver nanoparticles with a narrow size distribution were synthesized over the surface of two different commercial TiO(2) particles using a simple aqueous reduction method. The reducing agent used was NaBH(4); different molar ratios TiO(2):Ag were also used. The nanocomposites thus prepared were characterized using transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), dynamic light scattering (DLS) and UV-visible (UV-vis) absorption spectroscopy; the antibacterial activity was assessed using the standard microdilution method, determining the minimum inhibitory concentration (MIC) according to the National Committee for Clinical Laboratory Standards. From the microscopy studies (TEM and STEM) we observed that the silver nanoparticles are homogeneously distributed over the surface of TiO(2) particles and that the TiO(2):Ag molar ratio plays an important role. We used three different TiO(2)Ag molar ratios and the size of the silver nanoparticles is 10, 20 and 80?nm, respectively. It was found that the antibacterial activity of the nanocomposites increases considerably comparing with separated silver nanoparticles and TiO(2) particles.     

N-alkyl-polyethylenimine stabilized iron oxide nanoparticles as MRI visible transfection agents

An amphiphilic polymer, alkylated branched polyethylenimine (N-Alkyl-PEI), is synthesized and used for stabilization of hydrophobic superparamagnetic iron oxide (SPIO) nanocrystals in aqueous phase. Such composite particles are monodisperse without aggregation in physiological buffer as verified by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The nanocomposite system is capable of binding and delivering plasmid DNA for gene transfection while maintaining magnetic properties and biocompatibility. Transfection of cells showed that N-Alkyl-PEI2k stabilized magnetite nanoparticles were most effective in gene transfection comparing to unmodified PEI2k and PEI25k agents. Obvious MR signal darkening of transfected cells was observed under a clinical 3T MRI scanner. This multifunctional nanocomposite system provides a safe and efficient method for gene delivery with non-invasive imaging monitoring capability.     

Surface-modified superparamagnetic nanoparticles for drug delivery: preparation, characterization, and cytotoxicity studies

Superparamagnetic iron oxide nanoparticles have been used for many years as magnetic resonance imaging (MRI) contrast agents or in drug delivery applications. In this study, a novel approach to prepare magnetic polymeric nanoparticles with magnetic core and polymeric shell using inverse microemulsion polymerization process is reported. Poly(ethyleneglycol) (PEG)-modified superparamagnetic iron oxide nanoparticles with specific shape and size have been prepared inside the aqueous cores of AOT/n-Hexane reverse micelles and characterized by various physicochemical means such as transmission electron microscopy (TEM), infrared spectroscopy, atomic force microscopy (AFM), vibrating sample magnetometry (VSM), and ultraviolet/visible spectroscopy. The inverse microemulsion polymerization of a polymerizable derivative of PEG and a cross-linking agent resulted in a stable hydrophilic polymeric shell of the nanoparticles. The results taken together from TEM and AFM studies showed that the particles are spherical in shape with core-shell structure. The average size of the PEG-modified nanoparticles was found to be around 40-50 nm with narrow size distribution. The magnetic measurement studies revealed the superparamagnetic behavior of the nanoparticles with saturation magnetization values between 45-50 electromagnetic units per gram. The cytotoxicity profile of the nanoparticles on human dermal fibroblasts as measured by standard 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay showed that the particles are nontoxic and may be useful for various in vivo and in vitro biomedical applications.     

用原子力显微镜研究葡聚糖包覆纳米氧化铁微粒的形貌特征

采用化学共沉淀法合成了葡聚糖包覆的超顺磁纳米氧化铁微粒,用原子力显微镜对其分布状态、微粒形貌和尺度等进行了表征,并与透射电镜观察结果进行了比较。结果表明：葡聚糖包覆的超顺磁纳米氧化铁微粒大小均匀且有规律的定向分布,无团聚现象;透射电镜显示其核心氧化铁纳米粒子的外形主要为不规则的球形,粒径5～20nm被葡聚糖包覆后的纳米氧化铁微粒呈长方体,尺寸为（200-300）nm×（400-600）nm×（50-70）nm。     

Mechanistic principles of nanoparticle evolution to zeolite crystals

Precursor nanoparticles that form spontaneously on hydrolysis of tetraethylorthosilicate in aqueous solutions of tetrapropylammonium (TPA) hydroxide evolve to TPA-silicalite-1, a molecular-sieve crystal that serves as a model for the self-assembly of porous inorganic materials in the presence of organic structure-directing agents. The structure and role of these nanoparticles are of practical significance for the fabrication of hierarchically ordered porous materials and molecular-sieve films, but still remain elusive. Here we show experimental findings of nanoparticle and crystal evolution during room-temperature ageing of the aqueous suspensions that suggest growth by aggregation of nanoparticles. A kinetic mechanism suggests that the precursor nanoparticle population is distributed, and that the 5-nm building units contributing most to aggregation only exist as an intermediate small fraction. The proposed oriented-aggregation mechanism should lead to strategies for isolating or enhancing the concentration of crystal-like nanoparticles.     

Spatial structure of dye-doped polymer nanoparticle laser media

The spatial structure of dye-doped polymer-nanoparticle gain media, reported to generate spatially homogeneous single-transverse-mode laser beams, has been examined by electron microscopy in the nanometer scale. It is found that the distribution of the silica nanoparticles in the laser dye-doped polymer is fairly uniform. There is some aggregation of silica particles into loose nanoclusters. However, the nanocluster dimensions are smaller than those necessary to satisfy the conditions for internal interference in the visible spectrum. This explains the absence of macroscopic spatial inhomogeneities in the emission laser beams.     

纳米镍/介孔二氧化硅复合材料的组装及结构和性质 Ⅰ : 纳米镍/介孔二氧化硅复合材料的制备及结构表征

利用介孔组装,可以进行纳米复合材料结构和功能设计。通过溶胶-凝胶方法,采用混合、浸泡和氢热还原工艺,获得纳米镍/介孔二氧化硅复合材料。运用DSC、XRD、XPS、TEM等手段对纳米镍/介孔二氧化硅复合材料进行表征。结果表明,纳米金属Ni颗粒的尺寸由介孔SiO₂的结构和孔径分布决定,受还原温度和成分等影响,在8~20nm范围变化,浸泡法更容易获得纳米金属颗粒均匀分布的复合材料。由于SiO₂介孔结构连通,纳米Ni表面存在氧化,纳米颗粒存在于介孔中形成壳结构。介孔二氧化硅基体中添加稀土元素Ce,有利于增强介孔基体骨架强度,限制纳米颗粒聚集长大。      

Nanoparticles formed by complexation of poly-gamma-glutamic acid with lead ions

The present investigation describes the preparation and characterization of novel biodegradable nanoparticles based on complexation of poly-gamma-glutamic acid (gamma-PGA) with bivalent lead ion. The prepared nano-systems were stable in aqueous media at low pH, neutral and mild alkaline conditions. The particle size and the size of the complexes were identified by dynamic light scattering (DLS) and transmission electron microscopy (TEM) measurements. It was found that the size of the complexes depended on the pH and concentrations of gamma-PGA and lead ions. Particle sizes measured by TEM revealed that at low concentrations, nanosized particles were formed, however, at high concentrations of gamma-PGA and lead ions, the formation of large aggregates with a broad size distribution was promoted. The size of individual particles was in the range of 40-100 nm measured by TEM. The results from the DLS measurements showed that the low and high pH values in mixtures with high concentrations of gamma-PGA and Pb2+ ions favored the growth of large complexes. The gamma-PGA nanoparticles, composed of a biodegradable biomaterial with high flocculating and heavy metal binding activity, may be useful for various water treatment applications.     

Microstructure of nanoscale zinc oxide crystallites

Nanosized ZnO particles were prepared using a simple precipitation method. First, hydrozincite was obtained by adding Na₂CO₃ aqueous solutions with different concentrations to a zinc acetate precursor, previously dissolved in ethanol. We observed that the starting concentration of the precursors and the water content used for the hydrolysis influenced the size of the hydrozincite particles. The formation of the ZnO nanoparticles began after heating the hydrozyncite to 200 °C, and even when heating to 600 °C nanosized ZnO particles of 20-50 nm were obtained without agglomeration. The morphology and crystallinity of the obtained solids were characterized using XRD, SEM and TEM.