Concentrated colloids of silica-encapsulated gold nanoparticles: colloidal stability, cytotoxicity, and X-ray absorption

As an effort to develop a new, effective, nontoxic X-ray contrast agent, the concentrated colloids of silica-encapsulated gold nanoparticles (Au@SiO2 NPs) were fabricated and their colloidal stability, cytotoxicity, and X-ray absorption were investigated. The concentrated colloidal NPs were manufactured by forming a 4 nm-thick silica shell on the surface of each Au NP with 15 nm diameter, followed by enrichment to [Au] = 100 mM. They were very stable in water: the NPs were well separated each other without forming agglomerates and their optical property was very similar to that before enrichment. The colloidal stability of the NPs in biological environment was strongly dependent on their previous morphology in water. The NPs with minor shell damage were stable in phosphate buffered saline (PBS) solution: both in water and in PBS solution, they showed very similar morphology and optical property. However, the NPs with profound shell damage formed big agglomerates in PBS solution, resulting in the red-shift and broadening of the Au surface plasmon resonance peak. Cell viability and proliferation assessments revealed the biocompatibility of the Au@SiO2 NPs: no apparent cytotoxicity was observed even at 100 ppm NPs. The concentrated colloidal NPs showed very strong X-ray absorption. Their relative X-ray transmittance to water was comparable to that of a commercial agent. Considering these, the concentrated colloids of the Au@SiO2 NPs are suitable for an X-ray contrast agent.     

X-ray computed tomography imaging of a tumor with high sensitivity using gold nanoparticles conjugated to a cancer-specific antibody via polyethylene glycol chains on their surface

Contrast agents are often used to enhance the contrast of X-ray computed tomography (CT) imaging of tumors to improve diagnostic accuracy. However, because the iodine-based contrast agents currently used in hospitals are of low molecular weight, the agent is rapidly excreted from the kidney or moves to extravascular tissues through the capillary vessels, depending on its concentration gradient. This leads to nonspecific enhancement of contrast images for tissues. Here, we created gold (Au) nanoparticles as a new contrast agent to specifically image tumors with CT using an enhanced permeability and retention (EPR) effect. Au has a higher X-ray absorption coefficient than does iodine. Au nanoparticles were supported with polyethylene glycol (PEG) chains on their surface to increase the blood retention and were conjugated with a cancer-specific antibody via terminal PEG chains. The developed Au nanoparticles were injected into tumor-bearing mice, and the distribution of Au was examined with CT imaging, transmission electron microscopy, and elemental analysis using inductively coupled plasma optical emission spectrometry. The results show that specific localization of the developed Au nanoparticles in the tumor is affected by a slight difference in particle size and enhanced by the conjugation of a specific antibody against the tumor.     

Gold and silica-coated gold nanoparticles as thermographic labels for DNA detection

The infrared emissivity of Au and silica-coated Au nanoparticles (Au NPs) deposited on indium tin oxide substrates was investigated. NPs were irradiated with laser light at a frequency close to the Au plasmon resonance band, and the blackbody radiation emitted as a result was monitored with an IR camera equipped with an InAs array detector. The differences in temperature before and after laser irradiation were recorded (T-jumps) and were found to be directly proportional to the number of particles present on the slide and to the laser power used in the experiment. Coating Au NPs with silica increased the measured T-jumps 2-5 times, depending on the thickness of the silica shell. This was in agreement with the observation that silica has a much higher IR emissivity than Au. Both Au and silica-coated Au NPs were then tested as labels for thermographic DNA detection. Target DNA concentrations as low as 100 pM were recorded when Au NPs were used as labels and as low as 10 pM when silica-coated Au NPs were used.     

Ultrasonic solvent induced morphological change of Au colloids

Gold colloids were sonochemically synthesized in different solvents. It showed that different solvents resulted in different morphologies of Au colloids. In the mixture solution of ethanol/water, only spherical Au nanoparticles were obtained. In ethylene glycol, however, nanorod and platelet-like morphologies were formed together with spherically shaped Au nanoparticles, which resulted in optical absorption different from that of the former. Further experiment indicated that this originates mainly from different reduction rates of Au³⁺ ions in different solvents under the same sonochemical irradiation.     

Honey derivatized Au and Ag nanoparticles and evaluation of its antimicrobial activity

Biomolecules hosting the synthesis of nanoparticles has achieved considerable attention in recent decades due to their abundant availability, excellent biocompatibility and low toxicity. The present study demonstrates a rapid, cost-effective and eco-friendly fabrication of gold and silver nanoparticles at room temperature using natural honey as a source of stabilizing and reducing agent. The nanoparticles obtained were unambiguously characterized by using various characterization techniques such as transmission electron microscopy (TEM), UV-Visible absorption spectroscopy, X-ray diffraction and energy dispersive (EDX) X-ray analysis. The average size of Au and Ag nanoparticles are 10 and 12 nm respectively. Ag nanoparticles capped by honey exhibited superior antimicrobial activity while Au nanoparticles revealed passable activity against pathogenic bacteria and Candida albicans, including multi-resistant strains for the first time.     

Synthesis and agglomeration of gold nanoparticles in reverse micelles

Reverse micelles prepared in the system water, sodium bis-(2-ethylhexyl) sulfoccinate (AOT), and isooctane were investigated as a templating system for the production of gold nanoparticles from Au(III) and the reducing agent sulfite. A core-shell Mie model was used to describe the optical properties of gold nanoparticles in the reverse micelles. Dynamic light scattering of gold colloids in aqueous media and in reverse micelle solution indicated agglomeration of micelles containing particles. This was verified theoretically with an analysis of the total interaction energy between pairs of particles as a function of particle size. The analysis indicated that particles larger than about 8?nm in diameter should reversibly flocculate. Transmission electron microscopy measurements of gold nanoparticles produced in our reverse micelles showed diameters of 8-10?nm. Evidence of cluster formation was also observed. Time-correlated UV-vis absorption measurements showed a red shift for the peak wavelength. This was interpreted as the result of multiple scattering and plasmon interaction between particles due to agglomeration of micelles with particles larger than 8?nm.     

Synthesis of nanocomposite thin films containing Ag-Au alloy colloids for wavelength tunability

A chemical solution deposition route to synthesize silver-gold alloy colloids in thin films with diameters between 8–35 nm has been developed. Ag-Au alloy colloids were synthesized by the addition of silver ions to a polymer protected aqueous gold sol in presence of a seeding agent 'hydroxylamine hydrochloride,' followed by a heat-treatment under reducing atmosphere at temperatures ranging from 150–550°C. The resonance wavelength of Ag-Au alloy colloids exists between those of pure Ag (410 nm) and pure Au (525 nm) colloids, which can easily be controlled by selecting the molar ratio of Ag to Au. This allows the tunability of the absorption wavelength (hence the color) by using Ag-Au alloy colloids in thin films.     

Facile synthesis of Au nanoparticles supported on polyphosphazene functionalized carbon nanotubes for catalytic reduction of 4-nitrophenol

Carbon nanotubes (CNTs) functionalized with cyclotriphosphazene-containing polyphosphazenes (PZS) were found to cause the facile immobilization of Au nanoparticles on the surface. The PZS functional layers not only improved the dispersion of CNTs in aqueous solution but also used as a platform for subsequent immobilization of Au nanoparticles. The functionalized CNTs and the Au@PZS@CNTs nanohybrids were characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectrometer, X-ray diffraction, thermogravimetric analysis, Atomic absorption spectrum, and X-ray photoelectron spectroscopy. The results showed that the PZS layers with thickness of about 25 nm were formed uniformly on CNT surfaces by polycondensation between hexachlorocyclotriphosphazene and 4,4′-sulfonyldiphenol, and that high density of homogeneously dispersed spherical Au nanoparticles with average size of 6 nm was immobilized on their outer surface. Meanwhile, the catalytic activity and reusability of the Au@PZS@CNTs nanohybrids were investigated by employing the reduction of 4-nitrophenol into 4-aminophenol by NaBH₄ as a model reaction.     

Combined electrochromic and plasmonic optical responses in conducting polymer/metal nanoparticle films

Poly(3,4-ethylenedioxithiophene)/poly(styrene sulphonate) (PEDOT/PSS) aqueous dispersions were mixed with aqueous gold nanoparticle and aqueous silver nanoparticle colloids. PEDOT/gold nanoparticles (Au NP) and PEDOT/silver nanoparticles (Ag NP) films were obtained by solvent casting the corresponding aqueous solutions. The nanocomposite films showed the optical characteristics associated with both the surface plasmon absorption resonance of the metal nanoparticles and the excitation of the bipolaron band of the conducting polymer. As an interesting application we demonstrate the use of metal nanoparticles to tune the color of PEDOT based electrochromic films from blue to violet in the case of Au NP or green in the case of Ag NP.     

Cu2O-Au nanocomposites with novel structures and remarkable chemisorption capacity and photocatalytic activity

The decomposition of CuH nanoparticles in aqueous solution has been successfully developed as a novel method for the preparation of Cu₂O nanoparticles. In particular, we found that the decomposition of CuH nanoparticles in aqueous solution could be catalyzed by Au colloids, forming Cu₂O-Au nanocomposites. The composition and structure of the resulting Cu₂O-Au nanocomposites have been characterized in detail by inductively coupled plasma atomic emission spectroscopy, powder X-ray diffraction, N₂ adsorption-desorption isotherms, infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy. Their visible-light-driven photocatalytic activity toward various dye molecules has also been investigated. Depending on the Au:Cu ratio, Cu₂O-Au nanocomposites exhibit different novel nanostructures including a beautiful flower-like nanostructure that consists of polycrystalline Cu₂O, amorphous Cu₂O and Au colloids. We propose that the rapidly-generated bubbles of H₂ during the course of the catalytic decomposition reaction drive the simultaneously-formed Cu₂O to form amorphous curved thin foils and might also act as a template to assemble curved thin foils of amorphous Cu₂O, polycrystalline Cu₂O and Au colloids into uniform nanostructures. A Cu₂O-Au nanocomposite with a Cu:Au ratio of 40 exhibits remarkable chemisorption capacity and visible-light-driven photocatalytic activity towards methyl orange and acid orange 7 and is a promising chemisorption-photocatalysis integrated catalyst. The catalytic decomposition of the metal hydride might open up a new approach for the fabrication of other metal/metal oxide nanocomposites with novel nanostructures and properties.      

Fabrication of silica nanocapsules containing Ag/Au alloy nanoparticles by galvanic replacement reaction

A straightforward method has been developed to generate silica nanocapsules containing Ag/Au alloy nanoparticles (Ag/Au@silica) by in-situ galvanic replacement reaction between the silica-coated silver (Ag@silica) nanoparticles with aqueous chloroauric acid (HAuCl4). Ag/Au@silica exhibits an optical absorbance derived from the surface Plasmon resonance of the encapsulated Ag/Au alloy nanoparticle. The behaviour of chemical diffusion across the silica shells of Ag/Au@silica is also investigated. It is worthy to noting that this facile synthetic strategy could be amenable to the other systems that involve the use of different combination of materials for the core (Pd/Ag, Pt/Ag alloy nanoparticles) and for the shell (titania).     

A simple approach for facile synthesis of Ag,anisotropic Au and bimetallic (Ag/Au) nanoparticles using cruciferous vegetable extracts

We present a simple and straightforward approach for the synthesis and stabilization of relatively monodisperse Ag, Au and bimetallic (Ag/Au) nanoparticles by using cruciferous vegetable (green/red) extracts by simply adjusting the pH environment in the aqueous medium. The vegetable extracts act both as reducing and capping agents. The monometallic and bimetallic nanoparticles of Ag and Au so obtained were characterized by UV–visible spectroscopy, X-ray diffraction (XRD), dynamic light scattering (DLS) and transmission electron microscopy (TEM). It is shown that red cabbage extract can be used for the preparation of anisotropic Au nanoparticles. The formation of Au anisotropic nanoparticles was found to depend on a number of environmental factors, such as the pH of the reaction medium, reaction time, and initial reactant concentrations. Additionally, it is shown that these extract-stabilized Au and Ag nanoparticles can be used as a seed for preparation of bimetallic Au/Ag nanoparticles. For bimetallic alloy nanoparticles the absorption peak was observed between the two maxima of the corresponding metallic particles. The surface plasmon absorption maxima for bimetallic nanoparticles changed linearly with increasing Au mole ratio content in various alloy compositions. It has been shown that the formation of hollow Au spheres depends on the experimental conditions.     

Synthesis of complex shape gold nanoparticles in water-methanol mixtures

Gold nanoparticles with shapes which varied from spheres to multipods and polygons were prepared with a seedless approach in water/methanol mixtures in the presence of polyvinyl alcohol using sodium ascorbate as the reducing agent. The shape of Au nanoparticles is critically affected by the water/methanol ratio, as well as by the ratio of hydrogen tetrachloroaurate (HAuCl4) to sodium ascorbate and the concentration of HAuCl4 in the reaction mixture. A decreased ratio of water to methanol below 30/70 leads to the formation of multi-branched nanoparticles with the size in the range of 30-70 nm at relatively low HAuCl4 concentration, whereas polygons are formed when HAuCl4 concentration increases. The polyvinyl alcohol stabilized multi-branched Au nanoparticle colloids were stable at room temperature for a period of at least six-month.     

Characterization of silica-coated Ag nanoparticles synthesized using a water-soluble nanoparticle micelle

This article describes the synthesis of silica-coated Ag nanoparticles using a water-soluble nanoparticle micelle under basic conditions. Monodispersed Ag nanoparticles with a mean particle size of 7 nm were synthesized using AgNO₃ in the presence of ascorbic acid as a reducing agent. The Ag nanoparticles were easily re-dispersed into an aqueous solution by surface adsorption of surfactant molecules, indicating formation of water-soluble nanoparticle micelles. Silica-coated Ag nanoparticles ranging in size from 50 to 100 nm were obtained by controlling the surfactant, Ag nanoparticle and tetraethylortho silicate (TEOS) concentrations. Adsorbed surfactant monolayers on Ag nanoparticles were used as a template for the silica shell because of the hydrophobicity of TEOS. In all cases, the size of the resulting particles increased linearly as these concentrations increased. Based on transmission electron microscopy, all the Ag nanoparticles were completely covered with a silica shell. In most samples, however, Ag nanoparticle size increased from 7 to 50 nm due to evaporation of hexane by heating. Although mean particle size of silica-coated Ag nanoparticles was drastically altered, characteristic absorption peaks were observed at approximately 410 nm.     

Modifying Fe3O4-functionalized nanoparticles with N-halamine and their magnetic/antibacterial properties

Magnetic/antibacterial bifunctional nanoparticles were fabricated through the immobilization of antibacterial N-halamine on silica-coated Fe(3)O(4)-decorated poly(styrene-co-acrylate acid) (PSA) nanoparticles. The samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), X-ray diffraction (XRD), energy-dispersive X-ray spectrometry (EDX), Fourier transform infrared (FTIR), and thermogravimetric analysis (TGA). The N-halamine was developed from the precursor 5,5-dimethylhydantoin (DMH) by chlorination treatment, and experimental results showed that the loading amount of DMH on the silica-coated Fe(3)O(4)-decorated poly(styrene-co-acrylate acid) nanoparticles was adjustable. The as-synthesized nanoparticles exhibited superparamagnetic behavior and had a saturation magnetization of 18.93 emu g(-1). Antibacterial tests showed that the resultant nanoparticles displayed enhanced antibacterial activity against both Gram-positive and Gram-negative bacteria compared with their bulk counterparts.     

Controlling the aggregation behavior of gold nanoparticles

The aggregation of Au nanoparticles (NPs) in solution is influenced by cationic and oligocationic species. The polarization of the conduction electron oscillations in adjacent gold nanoparticles causes a new red-shifted plasmon absorbance attributed to the coupling of the plasmon absorbance of the particles. This appearance of an additional plasmon band is of particular interest to the field of SERS and has led to research works directed at the stabilization of small colloid aggregates in solution. The surface plasmon coupling can be tuned by controlling the aggregation of gold nanoparticles by the addition of some “cross-linking” agent. Here we develop a simple method to fabricate linear-chainlike aggregates of gold nanoparticles (so-called nanochains), tuning the linear optical properties in a wide wavelength range from visible to the near-infrared. The aggregation behavior and linear self-assembly mechanism of citrate-stabilized gold colloids as provoked by the addition of cetyltrimethylammonium bromide (CTAB) and 11-mercaptoundecanoic acid (MUA) are also analyzed. The line-assembly mechanism of gold nanochain is attributed to the preferential binding of CTAB molecules on a certain facet of gold NPs and the Au NP electrostatic interactions. We also found that the 11-mercaptoundecanoic acid was effective to prevent the further aggregation of CTAB-modified gold colloids.     

Magnetic properties of magnetite nanoparticles coated with mesoporous silica by sonochemical method

In this paper we present the magnetic properties of mesoporous silica-coated Fe₃O₄ nanoparticles. The coating of magnetite nanoparticles with mesoporous silica shell was performed under ultrasonic irradiation. The obtained mesoporous silica-coated magnetite nanoparticles were characterized by powder X-ray diffraction, focused ion beam-scanning electron microscopy, nitrogen adsorption-desorption isotherms and vibrating sample magnetometer. The hysteretic behavior was studied using first-order reversal curves diagrams. The X-ray diffraction result indicates that the extreme chemical and physical conditions created by acoustic cavitations have an insignificant effect on crystallographic structural characteristic of magnetite nanoparticles. Changes in the coercivity distributions of the magnetite nanoparticles were observed on the first-order reversal curves diagrams for the samples with coated particles compared with the samples containing uncoated particles of magnetite. The coated particles show an increased most probable coercivity of about 20% compared with the uncoated particles which can be associated with an increased anisotropy due to coating even if the interaction field distribution measured on the diagrams are virtually identical for coated/uncoated samples.     

氧化铅的添加对激光诱导玻璃中金纳米颗粒析出的影响

使用飞秒激光辐照和热处理相结合,通过引入PbO,实现了在含有金离子的硅酸盐玻璃内部,有空间选择性地析出大尺寸金纳米颗粒.通过吸收光谱,电子自旋共振谱和透射电镜测试研究了氧化铅对激光诱导金纳米颗粒析出的影响.实验结果表明,氧化铅的引入能抑制空穴捕获型色心生成,并促进金纳米颗粒的长大.     

Photoacoustic tomography of a rat cerebral cortex in vivo with au nanocages as an optical contrast agent

Poly(ethylene glycol)-coated Au nanocages have been evaluated as a potential near-infrared (NIR) contrast agent for photoacoustic tomography (PAT). Previously, Au nanoshells were found to be an effective NIR contrast agent for PAT; however, Au nanocages with their more compact sizes (<50 nm compared to >100 nm for Au nanoshells) and larger optical absorption cross sections should be better suited for in vivo applications. We sequentially injected Au nanocages into the circulatory system of a rat in three administrations and in vivo PAT was conducted immediately prior to the first injection and continued until 5 h after the final injection. A gradual enhancement of the optical absorption in the cerebral cortex, by up to 81%, was observed over the course of the experiment.