Structural and Optical Properties of Gold/Silica “Mushroom” Particles Prepared by Interfacial Templating

Complex shaped nanoparticles featuring structural or surface chemical patchiness are of special interest in both fundamental and applied research areas. This study reports the preparation and optical properties of gold/silica “mushroom” nanoparticles, where a gold particle is only partially covered by the silica cap. The synthetic approach allows precise control over the particle structure. The interfacial preparation method relies on partially embedding the gold particles in a polystyrene layer that masks the immersed part of the gold particle during silica shell growth from an aqueous solution. By adjusting sacrificial polystyrene film thickness and silica growth time, precise control over the coverage and cap thickness can be achieved. Correlative electron microscopy and single particle scattering spectroscopy measurements underline the high precision and reproducibility of the method. The good agreement between the measured and simulated single particle spectra supported by near‐field calculations indicates that the observed changes in the dipolar plasmon resonance are influenced by the extent of coverage of the gold core by the silica cap. The straightforward methods readily available for gold and silica surface modification using range of different (bio)molecules make these well‐defined nanoscale objects excellent candidates to study fundamental processes of programmed self‐assembly or application as theranostic agents.     

Synthesis of colloids based on gold nanoparticles dispersed in castor oil

New colloidal solutions of gold nanoparticles (AuNP), using castor oil as a nontoxic organic dispersant agent, were prepared via three different methods. In all three cases, tetrachloroauric(III) acid was employed as the gold source. The colloids were characterized by UV-Vis spectroscopy and transmission electron microscopy (TEM). The AuNP produced by the three methods were quasispherical in shape, however with different average sizes. The individual characteristics of the nanoparticles presented in each colloidal system were also confirmed by observation of absorption maxima at different wavelengths of visible light. Each method of synthesis leads to colloids with different grades of stability with respect to particle agglomeration.     

PEG-PLGA electrospun nanofibrous membranes loaded with Au@Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles for drug delivery applications

A PEGylated-PLGA random nanofibrous membrane loaded with gold and iron oxide nanoparticles and with silibinin was prepared by electrospinning deposition. The nanofibrous membrane can be remotely controlled and activated by a laser light or magnetic field to release biological agents on demand. The nanosystems were characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, and thermogravimetric analyses. The drug loading efficiency and drug content percentages were determined by UV-vis optical absorption spectroscopy. The nanofibrous membrane irradiated by a relatively low-intensity laser or stimulated by a magnetic field showed sustained silibinin release for at least 60 h, without the burst effect. The proposed low-cost electrospinning procedure is capable of assembling, via a one-step procedure, a stimuli-responsive drug-loaded nanosystem with metallic nanoparticles to be externally activated for controlled drug delivery.     

Synthesis,characterization, and thermal stability of SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript>/CR-Ag multilayered nanostructures

The controllable synthesis and characterization of novel thermally stable silver-based particles are described. The experimental approach involves the design of thermally stable nanostructures by the deposition of an interfacial thick, active titania layer between the primary substrate (SiO₂ particles) and the metal nanoparticles (Ag NPs), as well as the doping of Ag nanoparticles with an organic molecule (Congo Red, CR). The nanostructured particles were composed of a 330-nm silica core capped by a granular titania layer (10 to 13 nm in thickness), along with monodisperse 5 to 30 nm CR-Ag NPs deposited on top. The titania-coated support (SiO₂/TiO₂ particles) was shown to be chemically and thermally stable and promoted the nucleation and anchoring of CR-Ag NPs, which prevented the sintering of CR-Ag NPs when the structure was exposed to high temperatures. The thermal stability of the silver composites was examined by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). Larger than 10 nm CR-Ag NPs were thermally stable up to 300 °C. Such temperature was high enough to destabilize the CR-Ag NPs due to the melting point of the CR. On the other hand, smaller than 10 nm Ag NPs were stable at temperatures up to 500 °C because of the strong metal-metal oxide binding energy. Energy dispersion X-ray spectroscopy (EDS) was carried out to qualitatively analyze the chemical stability of the structure at different temperatures which confirmed the stability of the structure and the existence of silver NPs at temperatures up to 500 °C.     

A Method of Separation of Polydisperse Particles in the Plasma of Radio‐Frequency Discharge

A method of separation of polydisperse dust particles in the plasma of radio‐frequency (RF) capacitive discharge is considered. Investigations of plasma equipotential field enabled us to determine conditions for separation of polydisperse dust particles. The simplicity of the technology made it possible to obtain small dispersed particles of different materials. Samples of small dispersed microparticles of silica and alumina were obtained. The size and chemical composition of samples were examined using a Quanta 3D 200i scanning electron microscope (SEM, FEI, USA). The average size of separated silica nanoparticles was 600 nm, that of silica and alumina microparticles was 5 μm. Two separation methods were developed: the first one used a special trap and shape of the bottom electrode of RF discharge (for separation of microparticles) and the second used an electrical trap (for separation of nanoparticles). The graphs of particle size distribution were constructed using graphical and mathematical calculations. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and characterization of silica—titania core—shell particles

Abstract Nearly monodispersed particles of silica were prepared and coated with uniform layers of titanium dioxide in anatase phase by hydrolysis and condensation of titanium butoxide. The coating thickness could be altered by adjusting the concentration of reactants (titanium butoxide and water) and the amount of added silica particles. Different coating thicknesses were deposited and studied using optical absorption spectroscopy, electron microscopy and Fourier transform infra-red spectroscopy. It was found that silica particles of size 170 ±5 nm were coated with 23±5 nm thick layer of titanium dioxide. Alternatively titania particles of size 340±5 nm were synthesized by controlled hydrolysis of titanium ethoxide in the presence of sodium chloride. These particles were further coated with 135±5 nm thick layer of silica to investigate changes in properties after changing the shell material     

Photocatalytic degradation of methyl orange by gold silver nano-core/silica nano-shell

The silica nanoparticles (SiO₂ NPs), silver (Ag) NPs and gold (Au) NPs coated with SiO₂ NPs (core-shell) were prepared. The sizes and morphology of the particles were indicated. The three prepared NPs were used for photocatalytic degradation of methyl orange (MO) dye by xenon lamp. Rate of photocatalytic degradation reaction constant and lifetime were calculated for each catalyst. Moreover, the mechanism of the photocatalytic reaction was studied.     

Electron microscopy and EXAFS studies on oxide-supported gold-silver nanoparticles prepared by flame spray pyrolysis

Gold and gold-silver nanoparticles prepared by flame spray pyrolysis (FSP) were characterized by electron microscopy, in situ X-ray absorption spectroscopy (XANES and EXAFS), X-ray diffraction (XRD) and their catalytic activity in CO oxidation. Within this one-step flame-synthesis procedure, precursor solutions of dimethyl gold(III) acetylacetonate and silver(I) benzoate together with the corresponding precursor of the silica, iron oxide or titania support, were sprayed and combusted. In order to prepare small metal particles, a low noble metal loading was required. A loading of 0.1-1 wt.% of Au and Ag resulted in 1-6 nm particles. The size of the noble metal particles increased with higher loadings of gold and particularly silver. Both scanning transmission electron microscopy (STEM) combined with energy dispersive X-ray spectroscopy (EDXS) and X-ray absorption spectroscopy (XAS) studies proved the formation of mixed Au-Ag particles. In case of 1% Au-1% Ag/SiO₂, TEM combined with electron spectroscopic imaging (ESI) using an imaging filter could be used in addition to prove the presence of silver and gold in the same noble metal particle. CO oxidation in the presence of hydrogen was chosen as a test reaction sensitive to small gold particles. Both the influence of the particle size and the alloying of gold and silver were reflected in the CO oxidation activity.     

Synthesis and characterization of silica-coated nanoparticles of magnetite

Magnetic nanoparticles coated with silica have been subjected of extensive, and, in many aspects, also intensive investigations because of their potential application in different technological fields, particularly in biomedicine. This work was conceived and is being carried out in two main parts: (1) synthesis of the ferrimagnetic nanoparticles, specifically magnetite, and (2) coating these particles with tetraethyl orthosilicate (TEOS). The nanosized magnetite sample was prepared by the reduction–precipitation and the nanomagnetite particles were coated by the sol-gel method, based on the hydrolysis of tetraethyl orthosilicate (TEOS). The so obtained materials were characterized with powder X-ray diffraction (XRD), FTIR spectroscopy, saturation magnetization measurements, and ⁵⁷Fe Mössbauer spectroscopy at room temperature.     

Preparation and bactericide activity of gallic acid stabilized gold nanoparticles

In this work, gold nanoparticles with three different sizes (13.7, 39.4, and 76.7 nm) were prepared using a simple aqueous method with gallic acid as the reducing and stabilizing agent, the different sizes were obtained varying some experimental parameters as the pH of the reaction and the amount of the gallic acid. The prepared nanoparticles were characterized using X-ray diffraction, transmission electron microscopy, dynamic light scattering, and UV–Vis spectroscopy. Samples were identified as elemental gold and present spherical morphology, a narrow size distribution and good stabilization according to TEM and DLS results. The antibacterial activity of this gallic acid stabilized gold nanoparticles against S. mutans (the etiologic agent of dental caries) was assessed using a microdilution method obtaining a minimum inhibitory concentration of 12.31, 12.31, and 49.25 μg/mL for 13.7, 39.4, and 76.7 nm gold nanoparticles, respectively. The antibacterial assay showed that gold nanoparticles prepared in this work present a bactericide activity by a synergistic action with gallic acid. The MIC found for this nanoparticles are much lower than those reported for mixtures of gold nanoparticles and antibiotics.     

Structural and optical tunability of metallodielectric composites with gradual shell growth

Metallodielectric (gold@silica) composites were prepared by seed and grow method. The dielectric microspheres (core material) of an average size of 400 nm were synthesized by sol–gel method and gold nanoparticles (AuNPs) were prepared by reducing the chloroauric solution. Shell growth around silica (SiO₂) microspheres was carried out in a multistep layer-by-layer process. The synthesized composites were characterized using techniques such as field emission-scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and UV–Visible (UV–Vis) spectroscopy. FE-SEM and FTIR analyses have confirmed the functionalization of SiO₂ surfaces with the amine terminal group along with the gold shell growth. XRD analysis has given an average crystallite size of 12.3 nm for metallodielectric composites. Absorption spectra have demonstrated the dependence of surface plasmon resonance (SPR) peak on the successive shell growth by exhibiting a red shift.     

Stimulated Low-Frequency Raman Scattering in LaF<Subscript>3</Subscript> Suspensions

We observe stimulated low-frequency Raman scattering (SLFRS) caused by laser pulse interaction with acoustic vibrations of nanoparticles in water suspensions of LaF₃ nanoparticles. We show that frequency shifts of the scattering correspond to the eigenfrequencies of nanoparticles vibrations. LaF₃ nanoparticles were synthesized in the presence of glycine by a double jet precipitation technique at various initial concentrations of reagents. We investigate the morphologies and particle sizes as well as size distributions of the particles prepared using transmission electron microscopy (TEM) and dynamical light scattering (DLS). In view of the absorption spectroscopy, we show that the reaction system components and products have no absorption in the visible region, including λ = 694.3 nm. From the luminescence spectroscopy, we find also that they do not emit at λ = 694.3 nm excitation.     

Surface modification of gold nanoparticles and their monolayer behavior at the air/water interface

Gold nanoparticles were prepared by two different methods. The first method was chemically grafting the particles with different lengths of alkylthiol (C₆SH, C₁₂SH and C₁₈SH). For the second method, the Au particles were surface modified first by mercaptosuccinic acid (MSA) to render a surface with carboxylic acid groups which play a role to physically adsorb cationic surfactant in chloroform. This method was termed physical/chemical method. In the first method, the effects of alkyl chain length and dispersion solvent on the monolayer behavior of surface modified gold nanoparticles was evaluated. The gold nanoparticles prepared by 1-hexanthiol demonstrated the narrowest size distribution. Most of them showed narrower particle size distributions in chloroform than in hexane. For the physical/chemical method, the particles can spread more uniformly on the water surface which is attributed to the amphiphilic character of the particles at the air/water interface. However, the particles cannot pack closely due to the relatively weak particle-particle interaction. The effect of alkyl chain length was also assessed for the second method.     

Synthesis and characterization of mono-dispersed Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>:Er<Superscript>3+</Superscript>-coated SiO<Subscript>2</Subscript> nanoparticles by co-precipitation process

In this paper, a facile co-precipitation process for preparing mono-dispersed core–shell structure nanoparticles is reported. The 110 nm SiO₂ cores coated with an yttrium aluminum garnet (Y₃Al₅O₁₂) layer doped with Er³⁺ were synthesized and the influence of the concentration ratio of [urea]/[metal ions] on the final product was investigated. The structure and morphology of samples were characterized by the X-ray powder diffraction, Fourier transform IR spectroscopy and transmission electron microscopy, respectively. The results indicate that a layer of well-crystallized garnet Y₃Al₅O₁₂:Er³⁺ were successfully coated on the silica particles with the thickness of 20 nm. The near infrared and upconversion luminescent spectra of the SiO₂@Y₃Al₅O₁₂:Er³⁺ powders further confirm that a Y₃Al₅O₁₂:Er³⁺ coating layer has formed on the surface of silica spherical particles.     

The magnetic and hyperthermia studies of bare and silica-coated La<Subscript>0.75</Subscript>Sr<Subscript>0.25</Subscript>MnO<Subscript>3</Subscript> nanoparticles

The magnetic nanoparticles of La_0.75Sr_0.25MnO₃ perovskite manganite with a controlled size were prepared via sol–gel procedure, followed by thermal treatment and subsequent mechanical processing of the resulting raw product. The prepared materials were structurally studied by the XRD and TEM methods and probed by DC magnetic measurements. The nanoparticles of the mean crystallite sizes 11–40 nm exhibit T _C in the range of ≈310–347 K and the sample possessing 20-nm crystallites was identified as the most suitable for hyperthermia experiments. In order to obtain a colloidally stable suspension and prevent toxic effects, the selected magnetic cores were further encapsulated into silica shell using tetraethoxysilane. The detailed magnetic studies were focused on the comparison of the raw product, the bare nanoparticles after mechanical processing and the silica-coated nanoparticles, dealing also with effects of size distribution and magnetic interactions. The heating experiments were carried out in an AC field of frequencies 100 kHz–1 MHz and amplitude 3.0–8.9 kA m⁻¹ on water dispersions of the samples, and the generated heat was deduced from their warming rate taking into account experimentally determined thermal losses into surroundings. The experiments demonstrate that the heating efficiency of the coated nanoparticles is generally higher than that of the bare magnetic cores. It is also shown that the aggregation of the bare nanoparticles increases heating efficiency at least in a certain concentration range.     

硫醇衍生化的纳米金与癌胚抗原相互作用的光学分析

纳米金已在在药物靶向传输体系、疾病检测、分子识别、生物标签等领域有着广泛的应用,但是,由于纳米金的表面效应,大量的表面原子具有巨大剩余成键能力,使得纳米金粒子较容易团聚、沉聚,影响了其稳定性。为了实现对肿瘤靶标之一-癌胚抗原的痕量检测,需要制备出对癌胚抗原检测具有良好的增色效应与荧光增敏效应的纳米材料。该工作采用纳米金的硫醇衍生法制备了一种新型的硫醇衍生化的纳米金材料,并对此新型硫醇衍生化的纳米金材料的特性用透射电子显微镜,紫外-可见吸收光谱,荧光发射光谱和红外光谱等方法进行了研究。紫外-可见吸收光谱,荧光发射光谱的实验结果表明,在新的配体乙二硫醇存在下,有更多的电子从配体的轨道跃迁到与中心离子相关的轨道上,导致荧光增强。这种新型硫醇衍生化的纳米金与癌胚抗原作用时表现出增色效应与荧光增敏效应,而纳米金与癌胚抗原作用时看不到这种增色效应与荧光增敏效应。红外方法的研究结果表明,这种材料的蛋白增色机理为当硫醇衍生化纳米金与癌胚抗原蛋白作用时,体系中蛋白的—OH表现出更多的面外弯曲振动,有利于电子从硫醇衍生化纳米金配合物向蛋白转移而导致其增色和荧光增敏效应。因而这种新的硫醇衍生化纳米金材料比纳米金将具有更好的生物检测应用价值。     

Rapid synthesis of SiO<Subscript>2</Subscript> by ultrasonic-assisted Stober method as controlled and pH-sensitive drug delivery

In this paper, the monodisperse silica nanoparticles were prepared by ultrasonic-assisted Stober method, and it explained that the ultrasonic cavitation effect shortened the reaction time from the original hours to f5 min. The effects of ultrasonic time, ultrasonic power, and stirring speed on the morphology, composition, and specific surface area of silica nanoparticles were investigated by field emission electron microscopy (FE-SEM). The results showed that nanoparticles with the best dispersity and the most uniform morphology were obtained under the optimized conditions (ultrasonic time is 5 min, ultrasonic power is 160 W, and the magnetic stirring speed is 999 rpm). The phase composition of SiO₂ was characterized by high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), nano-size/zeta potential analyzer, and Fourier transform infrared spectroscopy (FT-IR). It showed that all typical peaks of samples are in line with the SiO₂ spectrum, the particle size distribution and zeta potential value of the silica is 615?±?35.6 nm and 59.87?±?0.91 mv, respectively, which further verified that the spherical silica nanoparticles with good dispersity can be synthesized in a very short time. Hemolysis test showed that nano-SiO₂ had high blood compatibility and biocompatibility when its concentration was less than 1 mg/mL. Doxorubicin (DOX·HCl) was regarded as a drug model to investigate the drug loading capacity of synthesized SiO₂; the results showed that the drug loading capacity and encapsulation efficiency reached 42.6?±?1.2 and 85.2?±?2.5%, respectively. Furthermore, the drug release experiments fitted well with the Higuichi equation with correlation coefficient (R²) of 0.9984, which further confirmed that the SiO₂/DOX drug delivery system has the controlled release property, and it also displayed pH-responsive behavior (at 96 h, the cumulative release of SiO₂/DOX in PBS solution with pH 7.4, 6.5, and 5.0 was 48.33, 62.31, and 94.86%, respectively). Therefore, this paper provides the possibility for developing more effective, safer, and more targeted controlled drug carriers.     

A study of oleic acid-based hydrothermal preparation of CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles

Nearly monodisperse, well crystalline, superparamagnetic CoFe₂O₄ nanoparticles with diameter of 6 nm were synthesized in oleic acid–water–pentanol system at 180 °C. Hydrothermal procedure, as an efficient and environment friendly alternative to organic decomposition methods, was investigated by variation of reaction conditions, and the particle formation mechanism was finally proposed (i.e., hydrolysis of metal oleates in organic phase, with size of the particles (5–8 nm) controlled by polarity-driven precipitation into water phase). As-prepared particles were hydrophobic due to coating by oleic acid. Further modification with dimercaptosuccinic acid led to water-dispersible particles with hydrodynamic diameter of 20 nm. Prepared particles were investigated by TEM, XRD, ICP-AES, light scattering, SQUID magnetometry, and Mössbauer spectroscopy.     

Flow Synthesis of Plasmonic Gold Nanoshells via a Microreactor

Gold nanoshells with tunable surface plasmon resonances are a promising material for optical and biomedical applications. They are produced through seed‐mediated growth, in which gold nanoparticles (AuNPs) are seeded on the core particle surface followed by growth of the gold seeds into a shell. However, synthetic gold nanoshell production is typically a multistep, time‐consuming batch‐type process, and a simple and scalable process remains a challenge. In the present study, a continuous flow process for the seed‐mediated growth of silica–gold nanoshells is established by exploiting the excellent mixing performance of a microreactor. In the AuNP‐seeding step, the reduction of gold ions in the presence of core particles in the microreactor enables the one‐step flow synthesis of gold‐decorated silica particles through heterogeneous nucleation. Flow shell growth is also realized using the microreactor by selecting an appropriate reducing agent. Because self‐nucleation in the bulk solution phase is suppressed in the microreactor system, no washing is needed after each step, thus enabling the connection of the microreactors for the seeding and shell growth steps into a sequential flow process to synthesize gold nanoshells. The established system is simple and robust, thus making it a promising technology for producing gold nanoshells in an industrial setting.     

Conventional wet impregnation versus microwave-assisted synthesis of SnO<Subscript>2</Subscript>/CNT composites

Carbon nanotubes decorated with SnO₂ nanoparticles were prepared by conventional and microwave-assisted wet impregnation. The composites were thoroughly characterized by X-ray diffraction, Raman spectroscopy, BET-surface area measurement, Scanning and transmission electron microscopy. The XRD studies revealed the formation of tetragonal phase of SnO₂. The microwave method produced CNTs heavily decorated with SnO₂ nanoparticles with average size 5 nm in a total reaction time of 10 min because of the rapid volumetric heating. DC conductivity increased significantly for the nanocomposite samples when compared with the pure CNTs. In electrical conductivity properties, sample prepared by microwave method was found to be superior to the one prepared by conventional procedure due to homogeneous distribution of nanoparticles.