Accumulation Of Au Research Articles

Accumulation and Phytotoxicity of Engineered Nanoparticles to Cucurbita Pepo

The effect of bulk and engineered nanoparticle (NP) Ag, Au, Cu, Si, and C at 250 and 750 mg/L on zucchini biomass, transpiration, and element content was determined. The pH of bulk and NP solutions prior to plant growth frequently differed. Nanoparticle Cu solution pH was significantly higher than bulk Cu, whereas for Ag and C, the NPs had significantly lower pH. Plants were unaffected by Au, regardless of particle size or concentration. NP Ag reduced plant biomass and transpiration by 49–91% compared to equivalent bulk Ag. NP Si at 750 mg/L reduced plant growth and transpiration by 30–51% relative to bulk Si. Bulk and NP Cu were phytotoxic but much of the effect was alleviated by humic acid. The shoot Ag and Cu content did not differ based on particle size or concentration. The accumulation of bulk Au was greater than the NP, but humic acid increased the accumulation of NP and bulk Au by 5.6-fold and 80%, respectively. The uptake of NP Si was 5.6–6.5-fold greater than observed with the bulk element. These findings show that the NPs may have unique phytotoxicity or accumulation patterns and that solution properties can significantly impact particle fate and effects.

Control of In Vivo Transport and Toxicity of Nanoparticles by Tea Melanin

Nanoparticles are unfamiliar to researchers in toxicology. Toxicity may be generated simply due to the reduction in size. Compounds that prevent or cure toxic materials may not work on nanoparticles. Furthermore, as there are more and more applications of nanoparticles in drug delivery and in vivo imaging, controlling the transport and toxicity will be primary concerns for medical application of nanoparticles. Gold nanoparticles (GNPs) if injected intraperitoneally into mice can enter hippocampus and induce cognitive impairment. GNPs caused a global imbalance of monoamine levels, specifically affecting the dopaminergic and serotonergic neurons. Pretreatment of tea melanin significantly prevented the deposition of GNPs in mouse brains, especially in the hippocampus. Pretreatment of melanin completely alleviated GNP‐induced impairment of cognition. Pre‐administration of melanin stably maintained monoamines at normal profiles. Melanin completely prevented the invasion of GNPs into the Cornu Ammonis region of the hippocampus shown by coherent anti‐Stoke Raman scattering microscopy. Here we show that the administration of tea melanin prevented the accumulation of Au in brain, the imbalance of monoamines, and the impairment of cognition in mice. The current study provides a therapeutic approach to toxicity of nanoparticles and a novel strategy to control the transport of GNP in mouse brain.

Biodistribution of gold nanoparticles and gene expression changes in the liver and spleen after intravenous administration in rats

Biodistribution of gold nanoparticles (AuNPs) in more than 25 organs were examined on 1 day, 1 week, 1 month and 2 months after a single intravenous (i.v.) injection in rats. Au was rapidly and consistently accumulated in liver (49.4 ± 50.4–72.2 ± 40.5 ng/g) and spleen (8.4 ± 5.0–9.5 ± 6.4 ng/g) throughout the entire timeframe of the study (2 months). Significant accumulation of Au in kidney (up to 5.5 ± 2.5 ng/g) and testis (up to 0.6 ± 0.1 ng/g) occurred from 1 month post-injection when Au level in urine and feces decreased. Significant increase of Au in blood occurred 2 months after injection, coincident with the delayed accumulation in kidney. Au accumulation in lungs was found at 1 day post-injection but decreased within a week. No accumulation of Au was found in the brain. Microarray results of liver and spleen point to significant effects on genes related to detoxification, lipid metabolism, cell cycle, defense response, and circadian rhythm. These results demonstrate that significant biodistribution of Au occurs in the body over 2 months after a single i.v. injection of AuNPs, accompanied by gene expression changes in target organs.

Reduction and accumulation of Au(III) by grape waste: A kinetic approach

Recovery of Au(III) in hydrochloric acid using grape waste was studied. The adsorption gel prepared from grape waste was found to highly selectively adsorb Au(III) showing negligible affinity for other precious metals and some base metal ions tested so far. The adsorption isotherm study exhibited the maximum loading capacity of the gel as high as 9.6 mol or 1.9 kg gold per kg dry weight of gel. XRD analysis and the digital micrograph of the gel taken after adsorption revealed the formation of gold particles during adsorption process which is associated with the high selectivity and high capacity of the gel for Au(III). Kinetic and electrochemical study was conducted at various temperatures to confirm an endothermic adsorption process following pseudo-first order kinetics.

Anomalous diffusion of Au in mega-electron-volt Au implanted SiO2∕Si(100)

Thermal annealing induced redistribution behavior of Au (3 MeV, 6.0×1015 ions cm−2), implanted into SiO2∕Si(100) substrates, has been investigated using Rutherford backscattering spectrometry and cross-sectional transmission electron microscopy (XTEM). Sequential annealing in the temperature range of 550−750 °C has been found to result in rejection of Au atoms from Si toward the SiO2∕Si interface. Above 750 °C a significant fraction of the implanted Au atoms has been found to back diffuse into deeper regions, well below the projected range Rp of Au. Direct annealing of a sample at 850 °C also shows a similar anomalous diffusion of Au into deeper regions, well below Rp. However, direct annealing at 1050 °C has been found to result in an enhanced accumulation of Au at a deeper layer. XTEM micrographs for the same sample show the presence of Au-rich nanoparticles and dislocations, decorated with Au-rich nanoparticles in this region. Trails of Au-Si liquid nanodroplets along with dislocations extending into this region have also been observed. The observed enhanced accumulation of Au in the deeper layer has been explained as due to efficient gettering of diffusing Au atoms at dislocations in this region, together with the migration of Au-Si liquid nanodroplets into it.

Controls of element dispersion in aeolian sand and calcrete-dominated regolith associated with gold mineralization in the Kraaipan greenstone belt, South Africa

This paper focuses on the geochemical controls and associated patterns of element dispersion in aeolian sand/calcrete regolith overlying the Goldridge Au mineralization in the Kraaipan greenstone belt, South Africa, and discusses possible sampling strategies. Regolith in the Goldridge area consists of in-situ weathered basement rocks, overlain by a colluvium and valley-filled sedimentary sequence comprising carbonate-impregnated pebbly to coarse/medium-grained sands at the base, followed by an upper reworked friable/laminated calcrete. These units are unconformably overlain by a fine- to medium-grained ferruginized aeolian sand. The thickest and most laterally extensive regolith sequence occurs along major drainages. Broad valleys and deep channels permitted widespread development and preservation of thick colluvial and alluvial sediments, which were subsequently overlain by aeolian sand. Gold shows variable dispersion patterns in aeolian sand, often with peak Au concentrations occurring in the central portions of the profile, coinciding with the transition zone between deep red and reddish-brown sands, that is geochemically characterized by a c . two-fold increase in the Fe/Mn ratio. The underlying calcite-rich laminated carbonate facies are accompanied by enhanced contents of CaO, MgO, Fe 2 O 3 , LOI, H 2 O − and a decrease in SiO 2 contents. The laminated calcretes are associated with the highest accumulation of Au in the entire regolith, whereas the calcrete-impregnated basal pebbly to sandy zone shows generally low but sporadically high Au content. Results of multivariate analysis of geochemical data suggest an association of Au with Fe–Mn oxides/ oxyhydroxides in the upper zones of aeolian sand. Increased influence of ferricrete nodules and underlying calcrete in the distribution pattern of Au and associated base metals occurs with depth. The use of stacked or additive element plots (e.g Cu+Ni+Co+Mn) show patterns that reflect various rock types or lithologies concealed beneath aeolian sand. The laminated to hardpan carbonate horizon and the basal zone of the aeolian sand horizon should therefore be sampled in exploration. An understanding of the spatial distribution of these regolith components is essential to maintain a consistent sample.

A Study of High‐Temperature and High‐Pressure Experiment of Correlativity between Deformational System of Au‐Bearing Rocks and Element Adjustment

Abstract Modelling of migration and accumulation of elements Au and Ag in rocks under temperatures of 350–450°C and a confining pressure of 300 MPa and axial pressure of 100–150 MPa is conducted. It is found that the contents of gold and silver get higher in metallic sulphides such as pyrite, chalcopyrite and sphalerite as well as in quartz and muscovite, and get lower in chlorite, biotite, seriate, albite and calcite, showing that tectono‐dynamics is one of the important factors for petrogenesis and metallogenesis.

Cathodic stripping voltammetric determination of ultratrace gold(III) at a bulk modified epoxy–graphite tube composite electrode in flow systems

An epoxy-impregnated graphite tube composite electrode bulk modified with 2-mercaptobenzoxazole was fabricated and employed for the determination of gold. A differential-pulse cathodic stripping procedure in conjunction with either continuous flow or flow injection was developed. Both open and closed circuit accumulation of Au(III) were investigated. The addition of Rhodamine 6G to the accumulation medium enhanced the sensitivity. Factors influencing the analysis were optimized. For continuous flow, precisions were 6.33% [relative standard deviation, n = 6, 5.00 × 10–8M Au(III), accumulation 10 min, open circuit] and 7.06% [n = 6, 1.00 × 10–9M Au(III), accumulation 10 min, closed circuit]. The detection limits (S/N = 3) were 6.7 × 10–9 and 1.9 × 10–10M Au(III) for open and closed circuit accumulations, respectively, with 10 min accumulation. For flow injection under similar conditions, the detection limits were 3.1 × 10–7M Au(III) (open circuit, injection volume 500 µl, 30.5 ng injected) and 2.9 × 10–9M (closed circuit, injection volume 500 µl, 0.29 ng injected). Selected metal ions and other inorganic and organic substances were examined for interferences. The developed method was applied to a certified water sample (US EPA WP 386), a sea-water sample and a pin-connector sample.

The relations between false gold anomalies, sedimentological processes and landslides in Harris Creek, British Columbia, Canada

Harris Creek is a Au-rich, cobble-gravel bed stream in southern British Columbia, Canada. A preliminary study, based on analysis of < 0.053 mm sediments and heavy mineral concentrates (SG > 3.2) from bulk sediment samples, identified accumulations of Au at breaks-in-slope of the stream gradient. This is consistent with theoretical models of heavy mineral transport by streams (Day and Fletcher, 1991). However, the breaks-in-slope also coincide with active landslides that might, because of the form of the Au anomalies, be interpreted as the source of the Au. To investigate this we have: (1) monitored erosion of the landslides and determined their Au content; and (2) used multi-element geochemistry (with Al, Mg, Na, Ba, Ti, P and Sr) to fingerprint the influence of one of the landslides on the composition of the < 0.053 mm fraction of the stream sediments. Material eroded from the toe of the Landslide # 1 forms soft clay-rich balls that are initially deposited in high-energy, bar-head environments. Observations and geochemical fingerprinting indicate that over a distance of 0.5 to 1.0 km downstream from the landslide these balls break down and release fine-grained sediment that is transferred from high- to low-energy (bar-tail) environments. Gold concentrations in the landslides are low (average 0.6 ppb) and the input of this material into Harris Creek dilutes Au values downstream from the landslide. The combined effect of accumulation of Au at breaks-in-slope in stream gradient and gradual dilution by landslide material, is to create peak Au values and false anomaly cut-off points downstream from a landslide. It is not clear if the association of active landslides with changes in stream gradient is coincidental or linked to local or catchment basin-scale geomorphic processes. Nevertheless, for Au and other elements transported in stream sediments as heavy minerals, the presence of anomalies and anomaly cut-offs near landslides and breaks-in-slope in stream gradient should be interpreted with caution.

Rutherford backscattering analysis of phosphorus gettering of gold and copper

The extrinsic gettering of Au and Cu by phosphorus diffusion in a classical or rapid thermal furnace has been analyzed by Rutherford backscattering (RBS) measurements. Accumulation of Au and Cu in the phosphorus-doped region has been clearly evidenced after classical or rapid thermal diffusion of phosphorus from a spin-on deposited silicon glass source in the temperature range 950–1050 °C for typical durations of 15 min and 25 s, respectively, confirming the existence of classical as well as a rapid thermal gettering effect.

Characterization of Au-Mediated a-Si:H Crystallization by In Situ Electrical Measurements

ABSTRACTThe Au-mediated crystallization of a-Si:H has been investigated by in situ electrical measurements and scanning electron microscopy. The a-Si:H structure was prepared by evaporation of Au thin films of different thicknesses (50 - 600 Å) onto intrinsic glow discharge deposited a-Si:H layers (≈ 5000 Å). A rapid increase in the electrical resistance was associated to the nucleation and growth of Si crystals inside the Au film. The growth process promotes the accumulation of Au at the Si grain boundaries forming a metallic network. This network controls the electric resistance at the end of the crystallization reaction. The kinetics of transformation has been studied by isothermal treatments over the 140 - 180 °C temperature range. An activation energy of 2.1 eV was measured. An analysis of resistance data obtained by constant heating rate treatments suggest the rupture of the network interconnections at T ≥ 170 °C. SEM pictures showing the formation of Au clusters confirmed this suggestion.

Accumulation of elemental gold on the alga Chlorella vulgaris

The accumulation of Au(0) by lyophilized preparations of the alga Chlorella vulgaris has been investigated. Gold is bound to the algae upon suspending dried algal cells in solutions containing hydrogen tetrachloroaurate (III). Relative amounts of ionic and atomic algal-bound gold were determined by thiourea extraction. It was found that the amount of algal-bound atomic gold produced from ionic gold increased with time. The effect of algal-bound gold concentration on the rate and extent of gold reduction was observed. It is suggested that at least three different classes of sites are available for gold binding and reduction. The effect of Au(0) accumulation on the binding ability of gold-bound algae was also investigated, and an apparent enhancement of gold binding ability is reported.

Thermal and ion-induced reaction of Ni–Au dilute alloys on Si

Redistribution of Au in Ni silicide formation by thermal annealing or ion beam mixing of Ni films with 1.4 at. % Au deposited on 〈100〉 Si was investigated using Rutherford backscattering spectrometry and glancing-angle x-ray diffraction. Annealing at temperatures of 300–350 °C results in the formation of Ni2Si with accumulation of Au at the Ni2Si/Ni interface. A similar redistribution of Au has also been found when the samples are irradiated with Xe ions at doses ≥2×1015 ions/cm2. This accumulation is contrary to the dispersion that one would anticipate in ballistic collisions and we believe that the Au accumulation is a result of thermodynamic forces in ion-induced reactions. In thermal annealing, the accumulation of Au impedes the supply of Ni and the second phase NiSi begins to form before the Ni film is consumed. With ion beam mixing, however, the accumulation of Au does not block silicide formation and Ni2Si continues to grow. We attribute the continued growth of Ni2Si to Au–Ni demixing within the collision cascade.

Cyanoaurate(III) Formation and Its Effect on Current Efficiency in Gold Plating

The cyanoaurate (III) ion has been found to form and accumulate in acidic or neutral gold plating baths containing cyanoaurate(I) as the source of gold. This trivalent gold species brings about a decrease in plating current efficiency because its reduction to gold metal requires three faradays per mole, whereas only one faraday is consumed to reduce one mole of Au (I). The accumulation of Au (III) should therefore be minimized to produce gold deposits with a thickness unaffected by bath age. This paper describes various methods for achieving this objective, which include the use of the so‐called “dimensionally stable anode” and a techniqe of chemically reducing Au (III) to Au (I).

The tissue distribution of gold, copper and zinc in animals treated with Au (III); species differences in the binding of these metals in the kidney

Whole body retention of Au and the distribution of Au, Cu and Zn have been measured in female rats, rabbits, guinea-pigs, hamsters and mice after either a single injection or multiple doses of Au(III). At 24 h after a single intraperitoneal injection whole body retention of Au was about 65% of the dose in the rabbit and 50% of the dose in other species. After five doses, retention (as a percentage of the total dose) ranged from 36% in mice to 49% in rats. Concentrations of Au in the kidneys were lowest in mice and highest in rats but, in all species, were greater than in other organs. In rats and guinea-pigs, but not in hamsters, rabbits and mice, treatment with Au(III) increased the Cu content of the kidneys and of the soluble fraction isolated therefrom. The latter from the rat and guinea-pig kidney contained both Au and Cu in association with a low molecular weight metalloprotein (metallothionein), which also contained Zn and was separated by ion exchange chromatography into three subspecies. Binding of Au by these metalloproteins appeared to be related to the renal accumulation of Cu. Apart from the mouse, in which renal accumulation of Au was low, slight damage resulted in the kidneys of all species after treatment with Au. It appears, therefore, that nephrotoxicity cannot be explained simply by the renal concentration of Au and the form in which it is accumulated within the tubular cells.