Colloidal Solution Of Au Nanoparticles Research Articles

Au nanoparticles coated with chitosan

This paper describes a method of coating metallic gold (Au) nanoparticles with chitosan (CS) shells in an aqueous solution. A colloidal solution of Au nanoparticles with a particle size of 16.5 ± 1.7 nm was prepared by reducing the Au ions (III) with sodium citrate in water at 80 °C. CS coating was achieved in an aqueous solution containing the Au nanoparticles by using CS as a shell source and sodium hydroxide as a pH adjuster at 25 °C. Ultraviolet-visible extinction spectroscopy and transmittance electron microscopy observation revealed that the Au nanoparticles were coated with CS shells. Additionally, the CS shell thickness could be varied in a range up to 2.2 nm by changing the CS concentration during the CS-coating process.

Laser ablation of Au–CuO core–shell nanocomposite in water for optoelectronic devices

Core–shell gold–copper oxide Au–CuO nanocomposites were synthesized using laser ablation of CuO target in colloidal solution of Au nanoparticles (NPs). The effect of laser fluence on the structural, morphological, electrical, and optical properties of Au–CuO nanocomposites was investigated using x-ray diffraction (XRD), atomic force microscope (AFM), scanning electron microscope (SEM), transmission electron microscope (TEM), photoluminescence (PL), Fourier transformed infrared spectroscopy (FTIR), Hall measurement, and UV–vis spectroscopy. X-ray diffraction results confirm the formation of polycrystalline Au–CuO NPs with monoclinic structure. The optical energy gap for CuO was 4 eV and for the Au–CuO core–shell nanocomposites was found to be in the range of 3.4–3.7 eV. SEM and TEM investigations revealed that the structure and morphology of Au–CuO core–shell nanocomposites were strongly depending on the laser fluence. A formation of Au–CuO nanospheres and platelets structures was observed. The photoluminescence data showed an emission of broad visible peaks between 407 and 420 nm. The effect of laser fluence on the dark and illuminated I–V characteristics of Au–CuO/n-Si heterojunction photodetectors was investigated and analyzed. The experimental data demonstrated that the photodetector prepared at optimum laser fluence exhibited photosensitivity of 0.6 AW−1 at 800 nm.

Controlled preparation and visible light photocatalytic activities of corn cob-like Au–ZnO nanorods

A facile method to prepare well-shaped nanohybrids of Au–ZnO nanorods (NRs) has been demonstrated, which is through polyvinylpyrrolidone-assisted in situ nucleation and growth of ZnONRs in the colloidal solution of Au nanoparticles (NPs). The obtained Au–ZnONRs shows uniform corn cob-like morphology with AuNPs evenly deposited on the surface of hexagonal ZnONRs and can be dispersed in aqueous solution to achieve photodegradation of organics. Moreover, the loading amount of AuNPs can be tuned to optimize the photocatalytic performance. The nanohybrid of Au–ZnONRs with optimized AuNP loading exhibits superior photocatalytic activity than ZnONRs alone, demonstrating ~90% Rhodamine B degradation within 18 h under the visible light of 420–780 nm, a wavelength range that does not overlap with ZnO absorption. The observed performance improvement is likely due to the coupling effect between ZnONRs and AuNPs, which functionalizes ZnONRs with visible light utilization and enhances charge separation. The strategy presented here not only provides a new approach for the controlled modification of 1D semiconductor nanostructures, but also holds good potential for applications such as degradation of organic pollutants.

Hydrogen emission under laser exposure of colloidal solutions of nanoparticles

We report the generation of molecular hydrogen from water by laser irradiation, without any electrodes and photocatalysts. A near infrared pulsed nanosecond laser is used for exposure of colloidal solution of Au nanoparticles suspended in water. Laser exposure of the colloidal solution results in formation of breakdown plasma in liquid and emission of H2. The rate of H2 emission depends critically on the energy of laser pulses. There is a certain threshold in laser fluence in liquid (around 50J/cm2) below which plasma disappears and H2 emission stops. H2 emission from colloidal solution of Au nanoparticles in ethanol is higher than that from similar water colloid. It is found that formation of plasma and emission of H2 or D2 can be induced by laser exposure of pure liquids, either H2O or D2O, respectively. The results are interpreted as water molecules splitting by direct electron impact from breakdown plasma.

Preparation of a Colloid Solution of Au/Silica Core-Shell Nanoparticles Surface-Modified with Cellulose and its X-ray Imaging Properties

Preparation of a Colloid Solution of Au/Silica Core-Shell Nanoparticles Surface-Modified with Cellulose and its X-ray Imaging Properties Objective: The aim of this paper is to describe the preparation of a colloid solution of Au nanoparticles that are coated with silica and simultaneously surface modified with carboxymethylcellulose (CMC) (Au/SiO2/CMC) and to investigate the X-ray imaging of mice using the colloid solution. Methods: The reduction of Au ions (III) with sodium citrate produced Au nanoparticles, and amino groups were introduced on the surface of the Au nanoparticles by using (3-aminopropyl)-trimethoxysilane. The Au nanoparticles with amino groups were silica coated by a sol-gel process using tetraethylorthosilicate, (3-aminopropyl)- triethoxysilane, water and sodium hydroxide in ethanol (Au/SiO2- NH2). After concentrating the as-prepared Au/SiO2-NH2 particle colloid solution by centrifugation, CMC was immobilized on the Au/ SiO2-NH2 particle surface with the addition of CMC to the Au/SiO2- NH2 particle colloid solution. Results: The Au/SiO2/CMC particles, with a size of 67.4 ± 5.4 nm containing a core of a single Au nanoparticle with a size of 17.9 ± 1.3 nm, were produced using the preparation conditions adopted in the present work. A computed tomography (CT) value that was as high as 344 ± 12 Hounsfield units (HU) was recorded for the Au/SiO2/CMC particle colloid solution with an Au concentration of 0.043 M. Its converted value was calculated by dividing the Au concentration into the recorded CT value and was 8.0×103 HU/M. This value was larger than that of Iopamiron 300, a commercial X-ray contrast agent. The Au/SiO2/CMC particle colloid solution was injected into the tail vein of a mouse and could be used to image the tissues. Conclusion: The Au/SiO2/CMC particle colloid solution obtained in the present work was successfully used for X-ray imaging.

Fabrication of quantum dot/silica core–shell particles immobilizing Au nanoparticles and their dual imaging functions

The present work proposes preparation methods for quantum dot/silica (QD/SiO2) core–shell particles that immobilize Au nanoparticles (QD/SiO2/Au). A colloid solution of QD/SiO2 core–shell particles with an average size of 47.0 ± 6.1 nm was prepared by a sol–gel reaction of tetraethyl orthosilicate in the presence of the QDs with an average size of 10.3 ± 2.1 nm. A colloid solution of Au nanoparticles with an average size of 17.9 ± 1.3 nm was prepared by reducing Au3+ ions with sodium citrate in water at 80 °C. Introduction of amino groups to QD/SiO2 particle surfaces was performed using (3-aminopropyl)-triethoxysilane (QD/SiO2-NH2). The QD/SiO2/Au particles were fabricated by mixing the Au particle colloid solution and the QD/SiO2-NH2 particle colloid solution. Values of radiant efficiency and computed tomography for the QD/SiO2/Au particle colloid solution were 2.23 × 107 (p/s/cm2/sr)/(μW/cm2) at a QD concentration of 8 × 10−7 M and 1180 ± 314 Hounsfield units and an Au concentration of 5.4 × 10−2 M. The QD/SiO2/Au particle colloid solution was injected into a mouse chest wall. Fluorescence emitted from the colloid solution could be detected on the skin covering the chest wall. The colloid solution could also be X-ray-imaged in the chest wall. Consequently, the QD/SiO2/Au particle colloid solution was found to have dual functions, i.e., fluorescence emission and X-ray absorption in vivo, which makes the colloid solution suitable to function as a contrast agent for dual imaging processes.

Preparation of Au/silica/poly(ethylene glycol) nanoparticle colloid solution and its use in x-ray imaging process

In this work, the authors performed X-ray imaging of mice using a colloid solution of Au nanoparticles that are coated with silica and subsequently surface-modified with poly(ethylene glycol) (PEG) (Au/SiO2/PEG). The silica-coating for Au nanoparticles and the amination for silica-coated particles were simultaneously performed in the presence of the Au nanoparticles, which were prepared by reducing Au ions (III) with sodium citrate in water at 80°C and by surface-modifying the Au nanoparticles with (3-aminopropyl)-trimethoxysilane (APMS), by a sol–gel process using tetraethylorthosilicate (TEOS), (3-aminopropyl)-triethoxysilane, water and sodium hydroxide (Au/SiO2-NH2). The surface modification of Au/SiO2-NH2 particles with PEG was performed by simply adding PEG with a functional group that reacts with an amino group to the Au/SiO2-NH2 particle colloid solution. A computed tomography value of the Au/SiO2/PEG colloid solution with an Au concentration of 0.129M was as high as 895 ± 8 HU. Mouse tissues were imaged following injection of the Au/SiO2/PEG particle colloid solution.

Three-dimensional microfabrication using local electrophoresis deposition and a laser trapping technique.

We describe a novel fabrication method of three-dimensional (3D) microstructures using local electrophoresis deposition together with laser trapping. A liquid cell consisting of two-faced conductive substrates was filled with a colloidal solution of Au nanoparticles. The nanoparticles were trapped by a laser spot and positioned on the bottom substrate, then deposited onto the surface by the application of electrical voltage between the two substrates. By moving the liquid cell downward while maintaining the deposition, 3D microstructures were successfully fabricated. The smallest diameter of the fabricated pillar was 500 nm, almost the same as that of the Airy disc. The Young's modulus of the fabricated structure was 1.5 GPa.

Growth of muscle cells on plasma-treated and gold nanoparticles-grafted polytetrafluoroethylene

Polytetrafluoroethylene (PTFE) was modified by Ar plasma with different exposure times. The plasma-activated surface was immersed in biphenyldithiol and subsequently in colloidal solution of Au nanoparticles. The changes in the surface wettability contact angle were examined by goniometry. Atomic force microscopy was used to determine the surface roughness and morphology. Changes in the chemical structure of the modified PTFE were studied using X-ray photoelectron spectroscopy (XPS) and electrokinetic analysis. The interaction of plasma-treated and grafted samples with vascular smooth muscle cell derived from the rat aorta was also studied. Specifically, the number and morphology of the adhered and proliferated cells on the PTFE were studied under in vitro conditions. The plasma treatment and the subsequent biphenyldithiol and Au nanoparticles grafting led to changes in the polymer surface chemistry, morphology, roughness and wettability. The polymer grafting with biphenyl-4,4′-dithiol (BFD) and subsequently with Au nanoparticles led to a decrease in the surface polarity. XPS measurements proved the presence of S and Au on the PTFE surface. Grafting with BFD and Au nanoparticles led to the decrease in surface roughness. In comparison with the pristine polymer, the plasma treatment and Au nanoparticles grafting increased the adhesion and proliferation of vascular smooth muscle cell.

X-ray imaging technique using colloid solution of Au/silica/poly(ethylene glycol) nanoparticles

This work describes X-ray imaging of mouse using colloid solution of silica coated Au (Au/SiO2) nanoparticles surface modified with poly(ethylene glycol) (PEG) (Au/SiO2/PEG). A colloid solution of Au nanoparticles was prepared by reducing Au ions (III) with sodium citrate. Au/SiO2 nanoparticles were fabricated by a sol–gel method using tetraethylorthosilicate, water and sodium hydroxide in ethanol in the presence of Au nanoparticles surface modified with (3-aminopropyl)trimethoxysilane. A computed tomography value of the Au/SiO2 colloid solution with an Au concentration of 0·083M was as high as 1421·2 Hounsfield units, which was higher than that of a commercial X-ray contrast agent with the same iodine concentration. Surface modification of the Au/SiO2 particles with PEG, or PEGylation of the particle surface, was performed using (3-aminopropyl)trimethoxysilane and PEG for the Au/SiO2 particles. Tissues of mouse could be imaged by injecting the colloid solutions of Au/SiO2 particles or Au/SiO2/PEG particles into it. The PEGylation provided an increase in residence time of particles in the mouse.

X-ray imaging technique using colloid solution of Au/silica core-shell nanoparticles

This work describes X-ray imaging of mouse using a colloid solution of silica-coated Au (Au/SiO2) nanoparticles. A colloid solution of Au nanoparticles with a size of 16.9 nm was prepared using hydrogen tetrachloroaurate (III) trihydrate as Au source and sodium citrate as reducing reagent. Silica coating of the Au nanoparticles was performed by modifying the Au nanoparticle surface with (3-aminopropyl)trimethoxysilane and then by depositing silica nuclei generated through a sol–gel reaction of tetraethyl orthosilicate in water/ethanol initiated with sodium hydroxide on the surface-modified surface, which produced Au/SiO2 particles with a size of 136.4 nm. A computed tomography value of the Au/SiO2 colloid solution with an Au concentration of 0.036 M was as high as 1,184.8 Hounsfield units, which was quite higher than that of a commercial X-ray contrast agent with the same iodine concentration as the Au concentration. Tissues of mouse could be imaged by injecting the Au/SiO2 particle colloid solution into them.

Deposition of gold nano-particles and nano-layers on polyethylene modified by plasma discharge and chemical treatment

Polyethylene (PE) was treated in Ar plasma discharge and then grafted from methanol solution of 1,2-ethanedithiol to enhance adhesion of gold nano-particles or sputtered gold layers. The modified PE samples were either immersed into freshly prepared colloid solution of Au nano-particles or covered by sputtered, 50 nm thick gold nano-layer. Properties of the plasma modified, dithiol grafted and gold coated PE were studied using XPS, UV–VIS, AFM, EPR, RBS methods and nanoindentation. It was shown that the plasma treatment results in degradation of polymer chain, creation of excessive free radicals and conjugated double bonds. After grafting with 1,2-ethanedithiol the concentration of free radicals declined but the concentration of double bonds remained unchanged. Plasma treatment changes PE surface morphology and increases surface roughness too. Another significant change in the surface morphology and roughness was observed after deposition of Au nano-particles. The presence of Au on the sample surface after the coating with Au nano-particles was proved by XPS and RBS methods. Nanoindentation measurements shown that the grafting of plasma activated PE surface with dithiol increases significantly adhesion of sputtered Au nano-layer.

Growth of two-dimensional arrays of uncapped gold nanoparticles on silicon substrates

A method of preparing large area patterned 2D arrays of uncapped gold (Au) nanoparticles has been developed. The pattern has been formed using self-assembly of uncapped Au nanoparticles. The Au nanoparticles were synthesized via toluene/water two phase systems using a reducing agent and colloidal solution of Au nanoparticles was produced. These nanoparticles have been prepared without using any kind of capping agent. Analysis by TEM showed discrete Au nanoparticles of 4 nm average diameter. AFM analysis also showed similar result. The TEM studies showed that these nanoparticles formed self-assembled coherent patterns with dimensions exceeding 500 nm. Spin coating on silicon substrate by suitably adjusting the speed can self-assemble these nanoparticles to lengths exceeding 1 μm.