Aqueous Suspensions Of Gold Nanoparticles Research Articles

Composite Iodine-gold Nanoparticles as a Contrast Agent in Computed Tomography.

Solutions of iodine-based compounds, due to their high X-ray attenuation coefficient, are widely used as contrast agents in computed tomography (CT) imaging. This paper investigates the attenuation properties of iodine and gold to develop nanoparticle-based contrast agents, for example, composite nanoparticles (NPs) with layers of iodine and gold or a mixture of NPs of gold and iodine. A theoretical formula is derived that gives the Hounsfield Unit (HU) for different weight-by-weight (w/w) concentrations of a mixture of blood + iodine + gold. The range of compositions for which iodine + gold mixture can give a suitable HU ≥250 upon being mixed with blood, is formulated. These estimates are derived from experiments on the variation of HU values in different compositions of aqueous solutions of iodine and available data for gold. It is seen that for an aqueous solution of iodine, the suitable HU of 250 (hence giving sufficient gray level to the CT image) can be obtained with w/w concentrations of iodine being 0.0044, 0.008, and 0.0097 for observations at 80, 100, and 120 kVp, respectively. The corresponding w/w concentrations of gold NPs would be 0.0103, 0.0131, and 0.0158. With these basic results, compositions of suitable mixtures of iodine and gold are also specified. Aqueous suspensions of gold NPs are suitable as contrast materials for CT imaging and can also be used as a component of a composite contrast material consisting of an iodine and gold mixture.

Inhibiting Au nanoparticle aggregation in freeze-thawing by presence of various additives

After freezing aqueous suspensions of gold nanoparticles (AuNPs) in the presence of various substances, the resulting aggregation of the nanoparticles was evaluated and the anti-aggregation effects of the different additives were compared. Many of the additives exhibited an anti-aggregation effects during freeze-thawing, the extent of which was greater at higher additive concentrations and the effects were 5 ~ 35% less than during the actual freeze-drying. Dextran and polyvinylpyrrolidone highly inhibited the aggregation even at markedly low additive concentrations (2 µg/mL). The use of a combination of a disaccharide (2 mg/mL of sucrose) and a sugar ester (20 µg/mL of sucrose palmitate) successfully preserved the redispersibility of the product after freeze-thawing while using each separately did not. Regarding the influence freezing and thawing conditions, a higher thawing temperature (from 4˚C to 60˚C) resulted in 10 ~ 20% better redispersibility of the AuNPs whereas the freezing temperature had no significant affect. The effect of freezing/thawing cycles of suspensions of AuNPs was also examined. The concentration of additive molecules on the surfaces of the frozen particles was monitored by In-situ Fourier transform IR spectroscopy. The collective findings of this study indicate that the additives essentially exert an anti-aggregation effect by slowing down the movement of the AuNPs.

Morphophysiological changes in the intact surface of rat skin under the application of silicon and gold nanoparticles

The effect of a course application of suspension of porous silicon and gold nanoparticles on the skin of female rats on the level of free radical oxidation and catalase activity in the skin homogenate was studied. MesoPSi samples were formed using the standard method of electrochemical etching of p-type c-Si wafers with a surface orientation of (100) and a specific resistance of 1-5 mOm x cm in a solution of hydrofluoric acid and ethanol (HF (50%): C2H5OH = 1: 1) at an etching current density of 60 mA / cm2 for 1 hour (45 minutes-hour). After this, mesoPSi films were separated from the silicon substrate by a short-term increase in the current density to 600 mA / cm2. Aqueous suspensions of porous silicon nanoparticles with sizes of the order of 100 nm were obtained by mechanical grinding of mesoporous silicon films in water. Aqueous suspensions of gold nanoparticles with an average size of 30-50 nm were obtained by laser ablation of gold targets in deionized water. A suspension of silicon and gold nanoparticles in physiological saline at a concentration of 0.2 mg / ml was applied once a day in the form of a thin layer on a shaved area of the skin of animals (interscapular region) and left to dry completely. Applications were carried out for 10 days. The studied silicon and gold nanoparticles did not change the initial content of malondialdehyde and catalase activity in the skin tissue but contributed to the activation of the rate of spontaneous lipid peroxidation.

Fabrication of nanoribbons by dielectrophoresis assisted cold welding of gold nanoparticles on mica substrate

Using alternating current electric fields, nanoribbons are fabricated from an aqueous suspension of gold nanoparticles (AuNPs) on mica substrate without resorting to further chemical functionalization of AuNPs. The potential and kinetic energies of AuNPs subjected to attractive forces from a mica substrate provide sufficient energy to pass the diffusion barrier of the gold atoms, which eventually leads to cold welding. A dielectrophoresis force exerted on polarizable particles in a non-uniform electric field contributes to the directed growth of the cold welding that occurs by adjusting the lattice structures of AuNPs. Depending on the concentration of the AuNP suspension, the frequency of the electric field, and the geometry of electrodes, various morphologies of nanoribbons are fabricated. It turns out that the welded region is nearly perfect to provide the same crystal orientation and strength as the rest of the nanostructures, which can be extensively utilized in the fabrication of various nanostructures.

Ultra-trace analysis of d-and l-aspartic acid applying one-by-one approach on a dual imprinted electrochemical sensor

An enantiomeric pair imprinted polymeric film, with embedded functionalized multiwalled carbon nanotubes, was developed following the ‘surface grafting from’ approach onto a gold nanoparticles decorated pencil graphite electrode. Double imprinting of chiral molecules in a single polymer motif, as a sensory platform, for the one-by-one evaluation of individual components of a racemic mixture, is a challenging task. The underlying state-of-art proposed for this purpose is novel and if this works well, any two simple molecules could be used as templates. In this work, a pencil graphite electrode was first dipped for the overnight in the aqueous suspension of gold nanoparticles. The electrode was then subjected to spin coating with a pre-polymerization mixture consisting a monomer (N-acryloyl-pyrrolidine-2,5-dione), templates (d- and l-Aspartic acid), a cross-linker (ethylene glycol dimethacrylate) in the presence of an initiator (α,α′-azoisobutyronitrile). As aspartic acid isomers have been found to be electro-inactive, their evaluation was feasible indirectly with the help of a potassium ferricyanide probe. The quantitation ability of the proposed sensor, with differential pulse anodic stripping voltammetric transduction, was found to be in the tune of 4.08ngmL−1 (S/N=3) for both the enantiomers in the real samples, which reportedly manifest several chronic diseases at their stringent limits.

Tuning the Interaction of Nanoparticles from Repulsive to Attractive by Pressure

We report a high pressure small-angle X-ray scattering (SAXS) study on concentrated aqueous suspensions of gold nanoparticles coated with a poly(ethylene glycol) (PEG)-based ligand shell. Analyzing the experimental SAXS data with a liquid-state theory approach, we find a pressure-induced transition of the interparticle interactions from repulsive to attractive in the pressure range from 1 to 4000 bar that also depends on the particle concentration. This transition is related to structural changes of the ligand shell which is compressed with increasing pressure. Our study highlights the important, yet unexplored role of pressure for the interaction of nanoparticle systems.

Decolorization of methylene blue in aqueous suspensions of gold nanoparticles using parallel nanosecond pulsed laser

Using 532 nm parallel nanosecond pulsed laser, the decolorization of methylene blue (MB) in aqueous suspensions of gold nanoparticles (GNPs) was studied. The effects of various experimental parameters, such as irradiation time, laser energy, and initial MB concentration on the decolorization rate were investigated. Experiments using real samples of textile dyeing wastewater were also carried out to examine the effectiveness of the method in more complex samples. From the results, the following conclusions may be drawn: (i) Under the optimum conditions (pH 7.19, 135 mJ laser energy, 4 mg/L MB concentration, and 11.6 mg/L GNP concentration), the rate of MB decolorization could reach 94% in 15 min. The decolorization follows pseudo–first-order kinetics; (ii) The amount of MB decreased rapidly during the decolorization. No intermediates of the decolorization could be detected by high-performance liquid chromatography. These observations indicate that MB was decolorized through a very rapid degradation mechanism; (iii) The rate of MB decolorization increased with the increase in laser energy (at laser energies of 0 to 135 mJ); and, (iv) The efficient decolorization of MB in real samples of textile dyeing wastewater was achieved at a decolorization rate of about 85% in 15 min.

Selective photocatalytic oxidation of aromatic alcohols to aldehydes in an aqueous suspension of gold nanoparticles supported on cerium(iv) oxide under irradiation of green light

Gold nanoparticles supported on cerium(IV) oxide powder showing strong absorption at around 550 nm due to surface plasmon resonance oxidized aromatic alcohols to corresponding aldehydes almost quantitatively in an aqueous suspension under irradiation of green light.

Gold nanoparticle membranes as large-area surface monolayers

An aqueous suspension of gold nanoparticles of sizes from 20 to 90 nm can be conjugated with mercaptosuccinic acid and exposed to a second phase of toluene containing an electrostatic coupler, tetraoctylammonium bromide, to organize the gold particles at the interface between water and toluene. The particles have an amphiphilic character similarly to Janus beads. The thus formed membrane can be transferred to a solid surface to yield centimeter-sized densely packed particle layers. We show that by changing the coupler concentration, the particle distances can be tailored, which modifies the optical properties.

Mineralization of organic acids in aqueous suspensions of gold nanoparticles supported on cerium(iv) oxide powder under visible light irradiation

Gold nanoparticles supported on cerium(IV) oxide powder showed strong absorption at around 550 nm due to localized surface plasmon resonance of Au and exhibited a higher level of activity than other Au-supporting samples in mineralization of organic acids in aqueous suspensions under irradiation of visible light (> ca. 520 nm).

Photodegradation of PAMAM G5-stabilized aqueous suspensions of gold nanoparticles

Gold nanoparticles are produced in the form of colloidal suspensions in water by ps laser ablation of a metallic target. The fifth generation of ethylenediamine-core poly(amidoamine) (PAMAM G5) is used as a capping agent. Thanks to the ability of PAMAM to encapsulate and stabilize gold cations within its inner cavities, it is possible to evidence, by simple UV–visible spectroscopy, a photo-fragmentation process induced by the 532 nm radiation, which is resonant with the absorption plasmon band of gold nanoparticles. This effect, that can be also exploited to control the size and shape of gold nanoparticles obtained with different procedures, arises from electron photo-ejection and subsequent charging and disintegration of existing gold nanoparticles into smaller size products.

Second harmonic generation from small gold metallic particles: From the dipolar to the quadrupolar response

Hyper Raleigh scattering, a common technique to investigate the second harmonic light scattered from a liquid suspension of molecular compounds and to determine their quadratic hyperpolarizability, has been used for aqueous suspensions of gold nanoparticles, the diameter of which ranges from 20 up to 150 nm. The hyper Rayleigh signal intensity was recorded as a function of the angle of polarization of the incident fundamental wave. For the particles with a diameter smaller than 50 nm, the response is dominated by the dipolar contribution arising from the deviation of the particle shape from that of a perfect sphere. For larger diameter particles, retardation effects in the interaction of the electromagnetic fields with the particles cannot be neglected any longer and the response deviates from the pure dipolar response, exhibiting a strong quadrupolar contribution. It is then shown that in order to quantify the relative magnitude of these two dipolar and quadrupolar contributions, a weighting parameter zeta(V) which equals unity for a pure quadrupolar contribution and vanishes for a pure dipolar response, can be introduced.