Synthesis and characterization of magnetic nanoparticles coated with a uniform silica shell

Magnetic nanoparticles with a proper surface coating are of outstanding interest for several applications, especially in the biomedical field. In this paper we present the synthesis of CoFe₂O₄ magnetic nanoparticles covered by a uniform silica shell. These particles were characterized by means of Transmission Electron Microscopy (TEM) and Small Angle Scattering of Polarized Neutrons (SANSPOL). This newly developed technique, taking advantage from the variation of magnetic contrast, allowed us to verify that the thickness of the silica shell can be accurately tailored through a very simple synthetic approach.     

Synthesis and physical characterization of magnetite nanoparticles for biomedical applications

Iron oxide nanoparticles for biomedical applications in the size range of 15–130 nm were prepared by either oxidative hydrolysis of ferrous sulfate with KOH or precipitation from ferrous/ferric chloride solutions. The magnetite particle size is controlled by variation of pH and temperature. The synthesized magnetite nanoparticles are partially oxidized as signaled by ferrous concentrations of below 24 wt% Fe²⁺ and lattice parameters of a₀ ≤ 8.39 Å which are smaller compared to 8.39 Å for stoichiometric magnetite. The extend of oxidation increases with decreasing particle size. Heating at 150–350 °C topotactically transforms the magnetite nanoparticles into stoichiometric tetragonal maghemite (ferrous ion concentration c_Fe²⁺=0 and a₀ = 8.34 Å) without significant particle growth. The magnetite–maghemite transformation is studied with thermal analysis, XRD and IR spectroscopy. The saturation magnetizations of the magnetite and maghemite particles decrease with decreasing particle size. The variation of M_s with particle size is interpreted using a magnetic core–shell particle model. Magnetite particles with d ≤ 16 nm show superparamagnetic behavior at room temperature whereas particles with diameter >16 nm display hysteresis behavior. These particles are candidates for biomedical applications, e.g. controlled drug release or hyperthermia.     

Synthesis and characterization of plasmon resonant gold nanoparticles and graphene for photovoltaics

Here we discuss the use in solar cells of graphene grown by chemical vapor deposition (CVD) and of plasmonic gold nanoparticles (Au NPs) deposited by sputtering. The Au NPs have been coupled with a-Si heterojunction solar cells, with an organic active layer used in organic photovoltaics, and with graphene. Extensive characterization of those three systems by the optical technique of spectroscopic ellipsometry, which is suitable to monitor and analyze the plasmon resonance of the Au NPs, by the microstructural technique of Raman spectroscopy, which is suitable to analyze graphene properties and doping, and by atomic force microscopy has been carried out. Those techniques highlighted interactions between Au NPs and silicon, polymer and graphene, which lead to variation in the plasmon resonance of Au NPs and consequently in the characteristics of the Au NPs/Si, Au NPs/polymer and Au NPs/graphene hybrids. Specifically, we found that an optimal size and density of Au NPs are able to enhance the efficiency of c-Si/a-Si heterojunction solar cells and that exceeding with Au NPs size and density causes device shortcut because of interface interdiffusion between silicon and gold. To discuss organic photovoltaics, Au NPs have been combined with an electro-donating conjugated polymer, the poly[1,4bis(2-thienyl)-2,5-bis-(2-ethyl-hexyloxyphenylenes)]. We found that there is a strong correlation between the thickness and morphology of the organic active layer, which affects the energy and amplitude of the Au NPs plasmon resonance. Finally, Au NPs have been deposited on graphene. We found that Au NPs show the plasmon resonance in the region where graphene is transparent and also yield p-type doping of graphene decreasing its sheet resistance.     

Synthesis and characterization of sol-gel silica films doped with size-selected gold nanoparticles

Homogeneous nanocomposite silica films uniformly doped with size-selected gold nanoparticles (AuNPs) have been prepared by a combined use of colloidal chemistry and the sol-gel process. For this purpose, stable thiol-functionalized AuNPs (DDT-AuNPs) were first synthesized by a two-phase aqueous/organic system and, subsequently, dispersed in an acid-catalysed sol-gel silica solution. The microstructural morphology of the samples was investigated by x-ray diffraction and field emission scanning electron microscopy. X-ray photoelectron spectroscopy (XPS) and UV-vis optical spectrophotometry were instead employed to investigate the elemental chemical behaviour and the evolution of the surface plasmon resonance (SPR) band of the AuNPs from their synthesis up to the formation of the Au-doped silica films. The results show that the size, shape and crystalline domains of the AuNPs remain unchanged during the entire preparation process, indicating that their aggregation or decomposition was prevented. XPS results show that the DDT-AuNPs lose the capping shells and oxidize themselves when dispersed in acid-catalysed sol-gel solutions, and that bare AuNPs are embedded in the SiO(2) films. A large broadening of the SPR band, observed for systems with DDT-AuNPs, suggests the presence of interface effects which cause a surface electron density lowering. Thiol chain detachment from the AuNPs determines an increase of the SPR peak intensity while the oxidation of the Au surfaces causes a red shift of its position. The latter is no longer observed in doped films, suggesting that no interfacial effects between bare AuNPs and the host medium are present.     

Synthesis and characterisation of cross-linked chitosan composites functionalised with silver and gold nanoparticles for antimicrobial applications

Abstract

We present a study of a range of cross-linked chitosan composites with potential antimicrobial applications. They were formed by cross-linking chitosan and siloxane networks and by introducing silver and gold nanoparticles (NPs). The aim was to investigate whether adding the metal NPs to the chitosan-siloxane composite would lead to a material with enhanced antimicrobial ability as compared to chitosan itself. The composites were synthesised in hydrogel form with the metal NPs embedded in the cross-linked chitosan network. Spectroscopic and microscopic techniques were employed to investigate the structural properties of the composite and the tensile strength of the structures was measured. It was found that the addition of metal NPs did not influence the mechanical strength of the composite. A crystal violet attachment assay results displayed a significant reduction in the attachment of E. coli to the cross-linked chitosan surfaces. Release profile tests suggest that the metal NPs do not contribute to the overall antimicrobial activity under neutral conditions. The contribution to the mechanical and antimicrobial properties from cross-linking with siloxane is significant, giving rise to a versatile, durable, antimicrobial material suitable for thin film formation, wound dressings or the coating of various surfaces where robustness and antimicrobial control are required.     

Laser-induced modification of polymeric beads coated with gold nanoparticles

A direct laser writing method for modifying colloidal crystals and single colloids is presented. This method takes advantage of the highly efficient conversion of photons into heat exhibited by gold nanoparticles. The easy control of experimental parameters allowed control of the spatial resolution of the patterns. This may open the way to practical applications for the technology.     

Synthesis, characterization and electrocatalytic activity of fused gold nanoparticles

This paper describes the synthesis of fused spherical gold nanoparticles (AuNPs) and their electrocatalytic activity towards the oxidation of hydroxylamine (HA). Fused AuNPs were prepared by one-pot synthesis using 2-mercapto-4-methyl-5-thiazoleacetic acid (TAA) as a stabilizing agent and sodium borohydride (NaBH4) as a reducing agent. The HR-TEM images showed that two individual AuNP were joined via on its surface with a size range of approximately 7 nm and a length of approximately 15 nm diameter. The pH studies showed that the synthesized fused AuNPs was stable at pH > 8. This indicated that the carboxylate ion present on the TAA molecule stabilized the AuNPs from aggregation. Further, the fused AuNPs were utilized for the electrocatalytic oxidation of hydroxylamine (HA) after immobilized them on (3-mercaptopropyl)-trimethoxysilane (MPTS) sol-gel film modified Au electrode. The AuNPs modified electrode showed an excellent electrocatalytic activity towards the oxidation of HA in 0.2 M phosphate buffer solution (pH 7.2) by shifting its oxidation potential to 100 mV less positive and enhancing its oxidation current for more than three times when compared to bare Au electrode. Further, it was found that the fused AuNPs modified electrode showed greater electrocatalytic activity towards HA than the spherical AuNPs modified electrodes.     

Synthesis and characterization of Fe–B nanoparticles for potential magnetic applications

The crystallization and structure of Fe–B nanoparticles (NPs) of different sizes formed in a single process by gas aggregation from Fe₈₀B₂₀ targets were analyzed by transmission electron microscopy. It is concluded that all NPs are covered by an amorphous Fe–B shell while the crystal structure of the NPs core depends on their size. Large NPs with diameters ≥30 nm are monocrystalline tetragonal Fe₃B, small diameter NPs (≤20 nm) are completely amorphous whereas in middle size NPs, with diameters between 20 and 30 nm, difference Fe–B phases (tetragonal Fe₃B and orthorhombic FeB) together with defaulted areas are observed. This work opens new possibilities to produce Fe–B NPs tailoring their magnetic properties by controlling their size and composition.     

Synthesis, characterization and electrical properties of carbon coated LiCoPO4 nanoparticles

Lithium cobalt phosphate (LiCoPO4) nanoparticles were synthesized using modified polyol process. Shape and size of LiCoPO4 nanoparticles were controlled by using poly (vinylpyrrolidone) (PVP) stabilizer. Coating of carbon over the LiCoPO4 nanoparticles was done using the resin coating process to enhance its conductivity. XRD and FTIR results respectively confirm the crystalline phase and structure of pure and carbon coated LiCoPO4 nanoparticles. SEM-EDX results confirm size and shape and also the presence of carbon over LiCoPO4 nanoparticles. Electrical conductivity of pure and carbon coated LiCoPO4 nanoparticles were evaluated by analyzing the measured impedance data using the win fit software. More than three orders of conductivity enhancement was observed in carbon coated LiCoPO4 nanoparticles when compared to pure ones. Further, transport properties like temperature dependence conductivity, AC conductivity, dielectric constant and electric modulus studies were made to find out the bulk and relaxation properties of LiCoPO4 nanoparticles.     

Cobalt nanoparticles coated with graphitic shells as localized radio frequency absorbers for cancer therapy

Graphitic carbon-coated ferromagnetic cobalt nanoparticles (C-Co-NPs) with diameters of around 7?nm and cubic crystalline structures were synthesized by catalytic chemical vapor deposition. X-ray diffraction and x-ray photoelectron spectroscopy analysis indicated that the cobalt nanoparticles inside the carbon shells were preserved in the metallic state. Fluorescence microscopy images and Raman spectroscopy revealed effective penetrations of the C-Co-NPs through the cellular plasma membrane of the cultured HeLa cells, both inside the cytoplasm and in the nucleus. Low radio frequency (RF) radiation of 350 kHz induced localized heat into the metallic nanoparticles, which triggered the killing of the cells, a process that was found to be dependent on the RF application time and nanoparticle concentration. When compared to carbon nanostructures such as single-wall carbon nanotubes, these coated magnetic cobalt nanoparticles demonstrated higher specificity for RF absorption and heating. DNA gel electrophoresis assays of the HeLa cells after the RF treatment showed a strong broadening of the DNA fragmentation spectrum, which further proved the intense localized thermally induced damages such as DNA and nucleus membrane disintegration, under RF exposure in the presence of C-Co-NPs. The data presented in this report indicate a great potential of this new process for in vivo tumor thermal ablation, bacteria killing, and various other biomedical applications.     

Synthesis and characterization of manganese containing mesoporous bioactive glass nanoparticles for biomedical applications

Mesoporous bioactive glass (BG) nanoparticles based in the system: SiO₂–P₂O₅–CaO–MnO were synthesized via a modified Stöber process at various concentrations of Mn (0–7 mol %). The synthesized manganese-doped BG nanoparticles were characterized in terms of morphology, composition, in vitro bioactivity and antibacterial activity. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) analysis confirmed that the particles had spherical morphology (mean particle size: 110?nm) with disordered mesoporous structure. Energy dispersive X-ray spectroscopy (EDX) confirmed the presence of Mn, Ca, Si and P in the synthesized Mn-doped BG particles. Moreover, X-ray diffraction (XRD) analysis showed that Mn has been incorporated in the amorphous silica network (bioactive glass). Moreover, it was found that manganese-doped BG particles form apatite crystals upon immersion in simulated body fluid (SBF). Inductively coupled plasma atomic emission spectroscopy (ICP-OES) measurements confirmed that Mn is released in a sustained manner, which provided antibacterial effect against Bacillus subtilis, Pseudomonas aeruginosa and Staphylococcus aureus. The results indicate that the incorporation of Mn in the bioactive glass network is an effective strategy to develop novel multifunctional BG nanoparticles for bone tissue engineering.     

Synthesis and characterization of ultrafine poly(vinylalcohol phosphate) coated magnetite nanoparticles

Nanosized magnetite (Fe3O4) particles showing superparamagnetism at room temperature have been prepared by controlled coprecipitation of Fe2+ and Fe3+ in presence of highly hydrophilic poly(vinylalcohol phosphate)(PVAP). The impact of polymer concentration on particle size, size distribution, colloidal stability, and magnetic property has been extensively studied. The aqueous suspension of magnetite, prepared using 1% PVAP solution is stable for four weeks at pH 5-8. X-ray diffractograms show the formation of nanocrystalline inverse spinel phase magnetite. Transmission Electron Microscopy confirmed well dispersed cubic magnetite particles of size of about 5.8 nm. Dynamic Light Scattering measurement shows narrow distribution of hydrodynamic size of particle aggregates. Infrared spectra of samples show strong Fe--O--P bond on the oxide surface. UV-visible studies show aqueous dispersion of magnetite formed by using 1% PVAP solution is stable at least for four weeks without any detoriation of particle size. Magnetization measurements at room temperature show superparamagnetic nature of polymer coated magnetite nanoparticles.     

微乳液体系制备Fe2B包覆纳米α-Fe及其性能研究

采用油包水(W/O)的微乳液体系制备纳米α-Fe.XRD、TEM分析表明,纳米α-Fe被Fe2B所包覆,其粒度在20～100 nm;激光粒度分析表明,纳米α-Fe存在团聚现象,但粒度分布窄;TG-DSC分析表明,纳米α-Fe在＞1100K时发生吸热的α-γ相变;磁强计检测表明,粉体具有铁磁性,其饱和磁化强度为1.14emu/g,剩余磁化强度为0.08emu/g,矫顽力为280Oe.     

Synthesis and electrochemical characterization of porous niobium oxide coated 316L SS for orthopedic applications

Niobium oxide was prepared using sol–gel process and coated on 316L stainless steel (SS) substrate via dip-coating technique. The surface characterization results after a thermal treatment revealed that the coated surface was porous, uniform and well crystalline on the substrate. The corrosion resistance and bioactivity of the porous niobium oxide coated 316L SS in simulated body fluid (SBF) solution was evaluated. The in vitro test revealed a layer of carbonate-containing apatite formation over the coated porous surface. The results indicated that the porous niobium oxide coated 316L SS exhibited a high corrosion resistance and an enhanced biocompatibility in SBF solution.     

Visual sensing of proteins using gold nanoparticles coated with polyphenolic glycoside

Gold nanoparticles combined with a polyphenolic glycoside (α-glucosylrutin) were prepared and applied for the selective detection of proteins. Glucosylrutin was coated onto gold nanoparticles with a particle size of 40 nm, without aggregates and color changes. The glucosylrutin-coated gold surface was preferentially adsorbed with concanavalin A, which has specificity against glucosides and mannosides. When the glucosylrutin-coated gold nanoparticles were mixed with concanavalin A, the color of the dispersion changed from red to reddish violet. The level of chromatic change was dependent on the concentration of concanavalin A. When other proteins (bovine serum albumin and peanut agglutinin) were added to the dispersion, no color change was observed. The molecular recognition site for detection of concanavalin A was the glycoside moiety, because the catechin-coated gold nanoparticles have no function in the detection of concanavalin A. Urchin-shaped glucosylrutin-coated gold nanoparticles were also useful for the visual sensing of concanavalin A.     

Synthesis, characterization, and biological applications of multifluorescent silica nanoparticles

Multifluorescent silica nanoparticles were synthesized by the St?ber method using conjugates of (3-aminopropyl)triethoxysilane and fluorescent dye-N-hydroxysuccinimide esters. The nanoparticles containing the fluorescent dyes were well dispersed and showed high, stable, and tunable fluorescence intensities. In addition, we prepared multifluorescent silica nanoparticles containing two kinds of fluorescent dyes and used the nanoparticles in biological applications. Flow cytometry analysis showed high and tuned fluorescence and multiple fluorescences from single nanoparticles with diameters of approximately 400 nm. Fluorescence microscopy analysis also showed high and tuned fluorescence, as well as multiple fluorescences from single nanoparticles and from cells labeled with multifluorescent silica nanoparticles. The intracellular distribution of nanoparticles was evaluated by confocal microscopy and electron microscopy. We discuss the advantages and demonstrate the usefulness of our nanoparticles in relation to commercially available fluorescent nanoparticles including quantum dots.     

金纳米粒子的制备及自组装

金纳米粒子以它独特的光学、电学和催化性质以及在纳米级电子线路中的应用潜力,受到人们越来越多的关注.本文主要评述了金纳米粒子的合成方法和自组装技术,即对各种制备方法和自组装的特点、纳米粒子的生长机理和自组装机理进行了介绍.展望了金纳米材料未来的研究方向和发展趋势.     

Synthesis and characterization of Fe doped CeO2 nanoparticles for pigmented ultraviolet filter applications

Iron doped CeO2 nanoparticles with doping concentrations between 0 and 30 mol% were synthesized by the co-precipitation method for potential application as a pigmented ultraviolet filtration material. Each sample was calcined in air and in argon. The iron solubility limit in the CeO2 lattice was found to be between 10 and 20 mol%. Raman spectroscopy results revealed that both iron doping and argon calcination increase the concentration of oxygen vacancies in the CeO2 lattice. Iron doping causes a blue-shift of the absorbance spectrum, which can be linked to the decreased crystallite size, as obtained by XRD peak broadening using the Scherrer formula. The undoped samples showed weak ferromagnetic behaviour whereas the doped samples were all paramagnetic.     

Covalent assembly of gold nanoparticles for nonvolatile memory applications

This work reports a versatile approach for enhancing the stability of nonvolatile memory devices through covalent assembly of functionalized gold nanoparticles. 11-mercapto-1-undecanol functionalized gold nanoparticles (AuNPs) with a narrow size distribution and particle size of about 5 nm were synthesized. Then, the AuNPs were immobilized on a SiO(2) substrate using a functionalized polymer as a surface modifier. Microscopic and spectroscopic techniques were used to characterize the AuNPs and their morphology before and after immobilization. Finally, a metal-insulator-semiconductor (MIS) type memory device with such covalently anchored AuNPs as a charge trapping layer was fabricated. The MIS structure showed well-defined counterclockwise C-V hysteresis curves indicating a good memory effect. The flat band voltage shift was 1.64 V at a swapping voltage between ±7 V. Furthermore, the MIS structure showed a good retention characteristic up to 20,000 s. The present synthetic route to covalently immobilize gold nanoparticles system will be a step towards realization for the nanoparticle-based electronic devices and related applications.     

Plasmonic properties of gold nanoparticles separated from a gold mirror by an ultrathin oxide

That a nanoparticle (NP) (for example of gold) residing above a gold mirror is almost as effective a surface enhanced Raman scattering (SERS) substrate (when illuminated with light of the correct polarization and wavelength) as two closely coupled gold nanoparticles has been known for some time. The NP-overmirror (NPOM) configuration has the valuable advantage that it is amenable to top-down fabrication. We have fabricated a series of Au-NPOM substrates with varying but thin atomic layer-deposited oxide spacer and measured the SERS enhancement as a function of spacer thickness and angle of incidence (AOI). These were compared with high-quality finite-difference time-domain calculations, which reproduce the observed spacer thickness and AOI dependences faithfully. The SERS intensity is expected to be strongly affected by the AOI on account for the fact that the hot spot formed in the space between the NP and the mirror is most efficiently excited with an electromagnetic field component that is normal to the surface of the mirror. Intriguingly we find that the SERS intensity maximizes at ~60° and show that this is due to the coherent superposition of the incident and the reflected field components. The observed SERS intensity is also shown to be very sensitive to the dielectric constant of the oxide spacer layer with the most intense signals obtained when using a low dielectric constant oxide layer (SiO(2)).