Silica-coated Gold Nanoparticles Research Articles

Reverse Microemulsion-Mediated Synthesis of Silica-Coated Gold and Silver Nanoparticles

A reverse microemulsion method is reported for preparing monodispersed silica-coated gold (or silver) nanoparticles without the use of a silane coupling agent or polymer as the surface primer. This method enables a fine control of the silica shell thickness with nanometer precision. As compared to the Stöber method reported for direct silica coating, which can only coat large gold particles ( approximately 50 nm in diameter) at low concentrations (<1.5 x 10(10) particles/mL), this new approach is capable of coating gold particles of a wide range of sizes (from 10 to 50 nm) at a much higher concentration ( approximately 1.5 x 10(13) particles/mL). Moreover, it enables straightforward surface functionalization via co-condensation between tetraethyl orthosilicate and another silane with the desired functional groups. The functional groups introduced by this method are readily accessible and thus useful for various applications.

Micropatterned Film of Silica-coated Gold Nanoparticles Formed by Covalent Bonds

Abstract With well-established surface-chemical properties, monodisperse silica-coated Au nanoparticles (Au@SiO2) were first functionalized with the silane reagent 3-gylcidoxypropyltrimethoxysilane (GPTS). Then, these epoxy-terminated Au@SiO2 nanoparticles could be easily assembled onto the silicon surface, which has been patterned with 3-aminopropyltriethoxysilane (APS) SAMs and octadecyltrichlorosilane (OTS) SAMs alternately, to form close-packed two-dimensional nanoparticle arrays by covalent bonding.

Optical strain detectors based on gold/elastomer nanoparticulated films

The application of two different optical effects is demonstrated for the detection of strain applied to elastomeric films. On one hand, dense coatings made of silica-coated gold nanoparticles (Au@SiO2 NPs), which are built up onto poly(dimethylsiloxane) (PDMS) elastomeric films, using the layer-by-layer (LbL) method, provide intense surface plasmon resonance (SPR) absorption. On the other hand, polystyrene spheres can be deposited as ordered monolayers to create patterned PDMS films with well-defined light diffraction. Both effects were used to monitor the structural damage of such PDMS films upon stretching, remaining both physical phenomena (absorption from the gold film and diffraction from the ordered structure) active for optical sensing applications in the early detection of structural damage in critical infrastructures.

X-Ray Absorption of Gold Nanoparticles with Thin Silica Shell

Silica-coated gold (Au) nanoparticles were prepared and their morphological and X-ray absorption properties were investigated. These core-shell type nanoparticles are very stable in aqueous media and may be suitable for an X-ray contrast agent in biological systems. Transmission electron micrographs confirmed well-separated and relatively homogeneous morphology of the nanoparticles in highly concentrated colloids. Peak position for Au plasmon resonance was red-shifted with increasing shell thickness. X-ray absorption by the colloids of silica-coated Au nanoparticles was stronger than that by those of silica-coated Agl nanoparticles, a recently investigated X-ray contrast agent, at similar experimental conditions.

X-Ray Absorption of Gold Nanoparticles with Thin Silica Shell

Silica-coated gold (Au) nanoparticles were prepared and their morphological and X-ray absorption properties were investigated. These core–shell type nanoparticles are very stable in aqueous media and may be suitable for an X-ray contrast agent in biological systems. Transmission electron micrographs confirmed well-separated and relatively homogeneous morphology of the nanoparticles in highly concentrated colloids. Peak position for Au plasmon resonance was red-shifted with increasing shell thickness. X-ray absorption by the colloids of silica-coated Au nanoparticles was stronger than that by those of silica-coated AgI nanoparticles, a recently investigated X-ray contrast agent, at similar experimental conditions.

Nanoscale Structural and Chemical Characterization of Silica Coated Gold Nanoparticles Using STEM 3D Imaging and EELS

Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2006

Highly Stable and Dense Colloids of Silica-Coated Gold Nanoparticles as X-Ray Absorbing Media for Medical Applications

not Available.

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.

Synthesis and self-assembly of silica-coated anisotropic gold nanoparticle films

Silica-coated anisotropic gold nanoparticles(Au@SiO2), including rod- and ‘dogbone’-like outlines with different aspect ratios,have been prepared using an improved Stöber method. The obtainedAu@SiO2 have a pure silica surface for straightforward and rapid self-assembly ontopoly(4-vinylpyridine) (PVP) functionalized quartz substrates. The large-scale assembliesexhibit highly reversible optical changes that can be observed spectroscopically or with thenaked eye when repeatedly cycled between a dry and wet process. The relationship amongthe optical properties of two-dimensional assemblies, the aspect ratio and shape of thegold nanoparticles and the environmental refractive index is also investigated.

Surface-functionalized silica-coated gold nanoparticles and their bioapplications

Monodisperse Au at SiO 2 nanoparticles has been functionalized with carboxylic groups for further bioconjugation with amino-terminated oligonucleotides. The oligonucleotide-modified Au at SiO 2 nanoprobes have been applied in the fast colorimetric DNA based on the sequence-specific hybridization properties of DNA. Self-assembling behavior of Au at SiO 2 nanoparticles was also investigated.

Synthesis, Functionalization, and Bioconjugation of Monodisperse, Silica-Coated Gold Nanoparticles: Robust Bioprobes

Herein, we report an efficient process for preparing monodisperse Au@SiO2 nanoparticles using homogeneous shaking and without the use of surface-coupling silane agents or large stabilizers. The resulting pure-silica surface of the Au@SiO2 nanoparticles is very important for straightforward surface functionalization with different functional groups via well-established silica surface chemistry. Subsequent covalent bioconjugation of the aldehyde-functionalized Au@SiO2 nanoparticles with various biomolecules is successfully employed to make robust nanoprobes for fast, colorimetric DNA and protein detection based on the sequence-specific hybridization properties of DNA and the specific binding affinity between proteins, respectively.

Magnetic and optical tunable microspheres with a magnetite/gold nanoparticle shell

Multifunctional core-shell microspheres consisting of a polystyrene 640 nm diameter core covered with a selectable number of layers of magnetite (12 nm) and silica-coated gold (15 nm) nanoparticles have been fabricated using the layer-by-layer (LbL) technique in aqueous solution. By varying the shell thickness and layer composition the magnetic and optical properties and the diameter of the colloids can be controlled independently. Optical spectra of the core-shell colloidal microspheres show a well-resolved Au surface plasmon peak in the visible which red-shifts with the number of adsorbed Au nanoparticle layers. The magnetic moment per sphere increases nearly linearly with the number of adsorbed magnetite nanoparticle layers, and the spheres can be assembled into chains of up to 1 mm length by deposition in a magnetic field.

Linear Assemblies of Silica‐Coated Gold Nanoparticles Using Carbon Nanotubes as Templates

Silica-coated gold nanoparticles were assembled on carbon nanotubes by polymer wrapping and layer-by-layer assembly (see Figure). The procedure was applied to ordered arrays of vertically aligned nanotubes, resulting in parallel nanotubes of compact nanoparticle monolayers for potential use in photonics.

Optical Properties of Nanoparticle‐Based Metallodielectric Inverse Opals

Metallodielectric inverse opals were prepared by co-crystallizing silica-coated gold nanoparticles and polymer spheres, followed by removal of the crystal template. The inverse opals exhibit a distinct reflectance peak, which results from Bragg diffraction due to the highly ordered 3D macroporous structure. Photonic band-structure calculations indicate that the characteristic reflectance peaks observed are signatures of the directional gap at the L point. It is demonstrated that the optical properties (the position and magnitude of the electromagnetic bandgaps) of the gold-silica nanocomposite inverse opals can be engineered by varying the nanoparticle morphology (core size and shell thickness) and/or the nanoparticle volume-filling ratio of the composite. The use of metallodielectric nanoparticles to form inverse opals offers a versatile approach to prepare photonic materials that may exhibit absolute bandgaps.

Coated Colloids with Tailored Optical Properties

Tailored optical properties have been imparted to polystyrene (PS) colloids of various sizes by the layer-by-layer (LbL) assembly of silica-coated gold (Au@SiO2) or silica-coated silver (Ag@SiO2) nanoparticles with different shell thicknesses and an electrostatically bridging polyelectrolyte, poly(diallyldimethylammonium chloride) (PDADMAC). The spectral position of the surface plasmon band of the composite colloid spheres is tailored through (i) the type of silica-coated nanoparticles used, (ii) the thickness of the silica shell, and (iii) the number of nanoparticle layers deposited. For thin silica shells ( 18 nm), nanoparticle core−core interparticle interactions are fully prevented and the plasmon band position is unaffected. Additionally, silica dissolution with HF leads ...

Heat dissipation in gold–silica core-shell nanoparticles

Heat dissipation from silica-coated gold nanoparticles in both water and ethanol solutions has been examined by time-resolved spectroscopy. The results show that the characteristic time constant for heat dissipation depends on the thickness of the silica shell and the solvent, even though the shells are much thicker than the thermal diffusion length corresponding to the time scale for these measurements. This is attributed to differences in the properties of the silica shells, that is, the thermal conductivity of the silica depends on how the shell is processed.

Synthetic Opals Based on Silica-Coated Gold Nanoparticles

High-quality solid colloidal crystalline assemblies have been prepared through the sedimentation of monodisperse silica spheres, each containing a single gold nanoparticle in its center. The metal centers provide a strong absorption at a well-defined wavelength that complements the Bragg reflection arising from the periodic structure of the opal. The optical properties of these systems were characterized through transmission and specular reflectance measurements. It is clearly shown that absorption and diffraction are basically independent of each other and their relative influence can be separated through infiltration with liquids of varying refractive index.

Sol−Gel Processing of Silica-Coated Gold Nanoparticles

Two procedures are presented which allow the homogeneous incorporation of silica-coated gold nanoparticles within transparent silica gels. Both UV−visible absorption spectra and transmission electron microscopy show that there is no aggregation of the metal particles during sol−gel transition. The optical properties of the gels are compared with those of the starting sols and interpreted on the basis of the porous structure of the gels and standard optical theories. Evidence is also shown of the potential of these methods for the preparation of gels with different particle sizes and shapes as well as with very high nanoparticle concentrations, which can be useful for several applications.