Coated Gold Particles Research Articles

Characterisation of Biooxidation Feed and Products for Improved Understanding of Biooxidation and Gold Extraction Performance

This paper presents a study on characterisation of refractory ore, biooxidation feed and product, and cyanidation tailings with the aim of understanding the causes of excessive continuous frothing, incomplete sulphide oxidation, high reagent consumption, high cyanidation residues and low overall recovery as encountered in biooxidation of refractory ores. Techniques involving carbon and sulphur speciation, Quantitative X-Ray Diffraction (QXRD), Scanning Electron Microscopy (SEM) and Optical Microscopy (OM) were used to characterise the ore samples, flotation concentrate (BIOX® feed), biooxidised product (BIOX® CIL Feed) and cyanidation tailings (BIOX® CIL Tails) from a biooxidation plant. The main minerals present in the ore were quartz (45%), chlorites (21%), plagioclase feldspar (13%), dolomite (5%), pyrite (2%) and mica group (2%). The flotation concentrate recorded 18% mica, and this was responsible for excessive frothing in the biooxidation circuit as confirmed by the QXRD analysis. The carry-over froth to the CIL circuit led to short-circuiting of poorly leached material into the cyanidation tailings, resulting in high cyanidation residues. Secondary refractory minerals; gypsum and jarosite, which were observed in the biooxidation product by the QXRD, have the potential to coat unreacted sulphide particles, leading to incomplete sulphide oxidation as observed here. Partially oxidised sulphides led to high consumption of reagents such as oxygen and cyanide during cyanidation. Gypsum and jarosite also encapsulated gold particles as observed in the BSED analysis. Coated gold particles had reduced access to lixiviants during the subsequent cyanidation process, leading to high leach residues. The biooxidised product (BIOX® CIL Feed) also recorded a high organic carbon content of 6.67, while analysis by BSED revealed the presence of graphitic carbon and coatings on gold surfaces; an indicator for high preg-robbing activities during cyanidation of the concentrate. Preg-robbing indices of 64.4% and 72.7% were recorded for the flotation concentrate (BIOX® feed) and BIOX® CIL feed respectively. The overarching effect of all the observations is a decrease in overall gold recovery.

Re-assessment of biolistic transient expression: An efficient and robust method for protein localization studies in seedling-lethal mutant and juvenile plants

Knowledge on the subcellular localization of target proteins in a plant mutant background is important for revealing the function of the genes investigated. However, in Arabidopsis and rice, mutant lethality is one major barrier to such studies. Here we describe an optimized bombardment-mediated transient expression approach for studying subcellular protein localization in Arabidopsis seedling of lethal mutants. The whole experiment comprises four stages: cultivation and preparation of plants, coating gold particles with plasmid DNA, delivery of DNA into plants via bombardment, plant incubation and gene expression analysis which include localization and dynamics, co-localization comparison with reporter proteins and functional analysis. The entire process takes about 3–10 days from plant cultivation to protein detection. It has a high efficiency and the results are reproducible. Additionally, this protocol is applicable for the transient expression of chimeric fluorescent fusion proteins in juvenile rice seedlings and leaf sheaths, saving time dramatically in comparison of generating transgenic rice plant.

Diagenetic alteration of a Mesozoic fluvial gold placer deposit, southern New Zealand

Gold paleoplacers become progressively more affected by diagenetic processes with age and burial. Mesozoic paleoplacer deposits in southern New Zealand display intermediate stages of diagenetic transformation compared to little-affected Late Cenozoic paleoplacers and strongly-affected Paleozoic and Precambrian paleoplacers. The Mesozoic (Cretaceous) diagenesis resulted in near-pervasive alteration, cementation and lithification of the paleoplacer. Lithic clasts and matrix have been extensively altered to illite, ferrous iron-bearing smectite-vermiculite, and kaolinite, and the cement consists mainly of clays and calcite. Diagenetic pyrite, marcasite, vivianite, and Mn oxide also contributed to cementation. Alteration occurred under near-surface (<500m depth) conditions with groundwater that had circumneutral pH, high alkalinity, and elevated dissolved K, Mg and Ca. Detrital albite remained unaffected by alteration. Detrital gold has been variably dissolved and redeposited, with widespread formation of gold overgrowths on the 1–10μm scales, with 1–3wt% Ag. Gold mobility was driven by reduced sulphur complexes in the low redox, high pH diagenetic environment. The overgrowth gold locally contributed to cementation of fine clastic grains, and has intergrown with diagenetic clays and Mn oxide. Post-diagenetic oxidation of the paleoplacer deposit has transformed much of the pyrite to ferric oxyhydroxide and deposited some ferric oxyhydroxide coatings on gold. These oxidation processes have had only minor effects on gold mobility and textures. Hence, the low redox conditions of diagenetic gold mobility were distinctly different from those typically associated with oxidation-related supergene gold mobility. Diagenesis can affect economics of paleoplacer mining by hindering rock disaggregation during processing, coating gold particles with secondary minerals, and increasing the clay content of the deposit, all of which can lower the efficiency of gold recovery.

Evidence for a C14 Frank-Kasper Phase in One-Size Gold Nanoparticle Superlattices.

The Frank-Kasper phases were already known in 1982 when quasi-crystals were discovered, but their complex architectures are now considered as making a link between simple close-packed periodic structures and some quasi-periodic ones. These tetrahedrally close packed structures are observed in many materials from elements to intermetallics as well as self-assembled soft materials like micellar systems, dendritric liquid crystals, star polymers, and more recently block copolymers or heated gold nanocrystal superlattices. We report here the existence of a Frank-Kasper phase with hexagonal symmetry (MgZn2 type, also labeled C14) in superlattices of monodisperse hydrophobically coated gold particles at room temperature obtained from suspensions in various solvents. The existence of such a structure in this system is analyzed in terms of geometrical parameters including gold core diameter, ligand length, and grafting density and an energetic approach based on van der Waals attraction. Hydrophobically coated gold nanoparticles is a new system that exhibits a Frank and Kasper phase built by one-size objects. This result opens a route toward a nanoparticle superlattice with complex structures and thus original physical properties.

A microarray MEMS device for biolistic delivery of vaccine and drug powders

We report a biolistic technology platform for physical delivery of particle formulations of drugs or vaccines using parallel arrays of microchannels, which generate highly collimated jets of particles with high spatial resolution. Our approach allows for effective delivery of therapeutics sequentially or concurrently (in mixture) at a specified target location or treatment area. We show this new platform enables the delivery of a broad range of particles with various densities and sizes into both in vitro and ex vivo skin models. Penetration depths of ∼1 mm have been achieved following a single ejection of 200 µg high-density gold particles, as well as 13.6 µg low-density polystyrene-based particles into gelatin-based skin simulants at 70 psi inlet gas pressure. Ejection of multiple shots at one treatment site enabled deeper penetration of ∼3 mm in vitro, and delivery of a higher dose of 1 mg gold particles at similar inlet gas pressure. We demonstrate that particle penetration depths can be optimized in vitro by adjusting the inlet pressure of the carrier gas, and dosing is controlled by drug reservoirs that hold precise quantities of the payload, which can be ejected continuously or in pulses. Future investigations include comparison between continuous versus pulsatile payload deliveries. We have successfully delivered plasmid DNA (pDNA)-coated gold particles (1.15 µm diameter) into ex vivo murine and porcine skin at low inlet pressures of ∼30 psi. Integrity analysis of these pDNA-coated gold particles confirmed the preservation of full-length pDNA after each particle preparation and jetting procedures. This technology platform provides distinct capabilities to effectively deliver a broad range of particle formulations into skin with specially designed high-speed microarray ejector nozzles.

Electrochemical codeposition of gold particle–poly(2-(2-pyridyl) benzimidazole) hybrid film on glassy carbon electrode for the electrocatalytic oxidation of nitric oxide

A nitric oxide (NO) sensor was developed by coating gold particles (AuPs) dispersed poly(2-(2-pyridyl) benzimidazole) (PPBZ) film on glassy carbon (GC) electrode by cyclic voltammetry. The PPBZ film modification enhances the electron transfer kinetics and the AuPs increase the surface area and electrocatalytic activities of GC electrode. A 4.04 fold increase in anodic current with 100mV shifting of the peak potential towards less positive side was observed for the composite film modified electrode compared to that of bare GC electrode. The electron transfer coefficient, electron transfer rate constant, diffusion coefficient and catalytic rate constant for the electrooxidation of NO were investigated. The amperometric measurements revealed a linear range of detection from 1.7×10−8 to 2.0×10−6M with a detection limit of 3.7nM (S/N=3) and sensitivity of 6.45AM−1cm−2. The modified electrode possessed remarkable stability and reproducibility towards NO detection and was successfully applied for the detection of NO released from the living tissues.

Coating Gold Particles with DNA (Biolistics)

Imaging and reconstruction of developing neurons require cells that are labeled in a way that distinguishes them from their neighbors. This can be achieved with ballistic labeling, which refers to the delivery of a cell label by means of carrier particles (tungsten or gold) propelled from a pressurized gun. Ballistic delivery can reach many dispersed cells in one shot and can deploy a wide variety of cell markers to neurons in diverse preparations. The three most commonly used types of ballistic labels are carbocyanine dyes, dextran-conjugated fluorescent markers, and DNA plasmids. The primary advantage of ballistic labeling is that multiple dispersed cells can be labeled quickly in live or fixed tissue. This article describes a protocol for coating gold particles with plasmid DNA, which can be used to label developing ganglion cells in retinal flat mounts.

Gene gun-mediated skin transfection with FL gene suppresses the growth of murine fibrosarcoma

Particle-mediated transfection is known as an efficient method of non-viral gene transfer. Flt3 ligand (FL) is a growth factor for hematopoietic progenitors; it promotes the growth of dendritic cells (DC). DCs are powerful antigen-presenting cells (APCs) and show a remarkable capacity to stimulate antigen-specific T-cell responses. In this study, we intended to investigate the suppressive effect on tumor growth by gene gun-mediated transfer of FL in a murine model. C57BL/6J mice were injected intradermally with MCA205 cells. DNA (pNGVL-hFLex)-coated gold particles were delivered to the mouse skin surrounding the target tumor. The expression of FL was determined by RT-PCR. Analyses by immunohistochemistry and fluorescence-activated cell sorter (FACS) revealed an increase in the number of DC after treatment with FL. Gene gun-mediated pNGVL-hFLex transfer significantly inhibited the growth of the MCA205 tumor. FL transfer markedly increased the number of CD11c(+) DCs in the tumor tissue. Further, the FL-transfected mice exhibited a significantly higher number of CD80(+) MHC-II cells. We successfully performed FL therapy using an in vivo gene gun in order to effectively mobilize DCs in situ and induce suppressive immunity.

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.

Removal of Gold Particles from Chromium Oxynitride Surface with Dilute Sulfuric Acid Solutions

Removal of gold particles (100 nm) from chromium oxynitride surface (CrON) has been investigated using dilute sulfuric acid solutions. Two types of gold nano-particles, one with a negative surface charge and the other with a positive charge achieved by adsorption of poly diallyl-dimethyl ammonium chloride (PDAC), were used. Particle removal efficiency (PRE) increases with sulfuric acid concentration and bath temperature. In 1:10 H2SO4:DI solution, increasing the bath temperature from 25 to 100 {degree sign}C increases the PRE from 21 to 99 %. Introduction of megasonic energy at 0.43 W/cm2 in a 1:10 H2SO4:DI bath at 35 {degree sign}C increases the PRE to 88 %. PDAC coated gold particles are difficult to remove as compared to uncoated particles due to their electrostatic interaction with the surface leading to stronger adhesion.

Novel plant transformation system by gene-coated gold particle introduction into specific cell using ArF excimer laser

Novel methods for foreign-gene introduction into specific cells are required for the functional analysis of specific cells. We report a new transfection method for intact plant cells that uses ArF excimer laser-induced shock waves to introduce foreign gene-coated gold particles into plant cells through the cell wall. Foreign gene (sGFP)-coated gold particles were randomly scattered on the surface of Torenia tissue samples; the laser was irradiated toward the gold particles using a hollow optical fiber and a quartz light-condensing tip to introduce the particles into the target cells. Treated plant tissue samples were then cultured for several weeks on the selection medium, and transformation was assessed by fluorescence microscopy and PCR. Irradiation-induced damage to the cells and coated DNA was insignificant, and the transformation efficiency was similar to that of biolistic transformation based on the particle number. Although this method requires a suitable laser setup and is time-consuming, it could be applied in transformation experiments on specific target cells. Moreover, this method can possibly be used to introduce not only DNA but also biologically active substances such as protein regulators or inhibitors, whose introduction into cells is difficult through the cell wall.

The use of biolistic inoculation of cassava mosaic begomoviruses in screening cassava for resistance to cassava mosaic disease

Inoculation of cassava with infectious clones of cassava mosaic geminiviruses ( Geminiviridae: Begomovirus) and total DNA extracts from plants infected with well-characterised viruses was evaluated using the Bio-Rad Helios Gene Gun System. Total DNA extracts from infected plants and cloned viruses were produced for coating gold particles and bombardment onto new cassava genotypes, 96/1089A, 96/1039, 96/0160, 96/0304 and three local landraces TME 117, TME 3 and TME 4. Cloned DNA of a Kenyan isolate of the recombinant variant of East African cassava mosaic virus (EACMV-UG2-[Ka]), was only infectious to TME 117 (7/10 plants), 3 weeks post-inoculation with mild infection symptoms in the newly developing leaves. Biolistic inoculation with a chimeric pseudorecombinant virus between DNA A and B components from EACMV-[Ke-Kilifi] and EACMV-UG2-[Ka], respectively, was infectious to TME 117, 96/1039 and 96/0304 and developed very severe and persistent symptoms. TME 3 and TME 4 also developed symptoms, 12 days post-inoculation (d.p.i.). Total DNA extracts of ACMV and EACMV-[Ke-Kilifi] resulted in serious infections with symptoms already evident, 10 d.p.i. In general, biolistic inoculation trials with total DNA extracts resulted in a higher number of infected plants expressing symptoms at a much earlier stage (10–12 d.p.i.) compared with trials inoculated with virus clones.

Transient Expression of Anthocyanin in Developing Wheat Coleoptile by Maize C1 and B-peru Regulatory Genes for Anthocyanin Synthesis.

Maize transcription factors for the genes of anthocyanin synthesis pathway, C1/B-peru, were delivered into developing wheat coleoptiles by a particle bombardment method. Anthocyanin pigments were induced as discrete red spots and their number reached about 60 spots per coleoptile, compared to about 20 diffused blue GUS spots, which were induced by the GusA gene transferred concomitantly. Coleoptiles of seedlings collected 36 h after germination were most suitable tissue for the expression of delivered foreign genes. One to five μg of plasmid DNA for coating gold particles was sufficient for induction of anthocyanin and GUS, indicating that the transferred gene was expressed efficiently in coleoptile cells. Helium gas pressure (900, 1100, 1300 or 1500 pounds per square inch) and distances (10, 15, or 20 cm) between the stopping screen and coleoptile did not affect significantly the efficiency of gene transfer. Seedlings arranged in a circle with a 1-cm radius on a MS medium plate were targeted well by gold particles. The results showed that the wheat coleoptile was a good target tissue for transient assay of wheat genes and that C1/B-peru can be used as a reporter gene.

Endothelial cell—mediated uptake of a hepatitis B virus: a new concept of liver targeting of hepatotropic microorganisms

The liver is a target for many infectious agents, most notably hepatitis viruses. However, several receptor molecules identified so far for hepatitis viruses were found to be ubiquitously expressed and can thus not account for efficient liver targeting. Using a model hepatitis B virus, the duck hepatitis B virus (DHBV), we have obtained data indicating that scavenging liver sinusoidal endothelial cells (LSEC), rather than hepatocytes themselves, play the key role in the initial uptake of viral pathogens into the liver. Experiments with fluorescent viral particles and coated gold particles in test animals, as well as in primary liver cell culture, demonstrated a preferential uptake of the viral substrates into LSEC. Intracellularly, fluorescent virus particles internalized by LSEC colocalized with the DHBV receptor, carboxypeptidase D, suggesting receptor-mediated rescue from lysosomal degradation. To comply with the high efficiency by which hepatitis B viruses infect hepatocytes in vivo, we propose that viruses initially scavenged by LSEC are thereafter released to infect adjacent hepatocytes, the only cells capable of replicating these viruses. Such a model of primary uptake into LSEC may illustrate a general mechanism by which blood-borne hepatotropic agents are targeted to the hepatocytes in the liver.

Endothelin-1 Responsiveness of a 1.4 kb Phospholamban Promoter Fragment in Rat Cardiomyocytes Transfected by the Gene Gun

The transcriptional regulation of an isolated rat phospholamban (PL) promoter fragment in rat cardiomyocytes was analyzed by applying a new method to reach substantially higher transfection efficiencies: gene gun biolistics. The gene gun transfection method was optimized for application to primary cultures of rat neonatal cardiomyocytes. Cells, cultured at different densities (0.75–1.50×105cells/cm2) in serum-free medium, were transfected with DNA coated gold particles. A transfection efficiency of up to 10% could be achieved (compared to <1% with other methods) by the gene gun as checked using a RSV- β-Gal construct. Cardiomyocytes were stimulated by endothelin-1 (ET-1) (10−8M) to induce hypertrophy, thereby yielding the characteristic changes in gene expression (upregulation of Atrial Natriuretic Factor (ANF) and downregulation of PL). The basal activity of an ANF promoter fragment (increasing from the lowest to highest density 2.6-fold) and its ET-1 inducibility (only significant upregulation of 2.6-fold, at lowest density) appeared to be dependent on the plating density of the cardiomyocytes. A PL promoter fragment was isolated, sequenced and 1.4 kb was subcloned in a luciferase reporter vector. The basal activity of the PL promoter fragment was not dependent on the plating density. ET-1 did not downregulate the PL promoter, rather a significant upregulation (1.4-fold) was found at the highest plating density. In conclusion, plating density of the cardiomyocytes can influence promoter activity as shown with an ANF promoter fragment. A newly isolated and sequenced rat PL promoter fragment did not direct gene expression as expected on basis of downregulation of the PL gene by ET-1 observed in this model.

Semi-real time imaging of the expression of a maize polyubiquitin promoter-GFP gene in transgenic rice

We have introduced the green fluorescent protein gene under the control of the maize ubiquitin promoter into rice embryos by microprojectile bombardment. Transient expression of GFP on the surface cells in the rice embryos depended on the localization of DNA coated gold particles. Bialaphos-resistant rice calli were produced by bombardment with a two plasmid mixture of pUbi-GFP and pDM302 carrying the coding region of the bar gene. Microscopic fluorescent image analyses indicated that the area of GFP expression increased and spreaded on the transgenic rice calli after heat stress.

Factors influencing transient gene expression in bean (Phaseolus vulgaris L.) using an electrical particle acceleration device

The parameters influencing transient expression of the betaglucuronidase gene in bean embryonic axes, cotyledons, apical meristems and leaves were evaluated after gene delivery with an electrical particle acceleration device. A calciumspermidine procedure for coating gold particles with DNA resulted in higher levels of GUS expression with lower concentrations of gold particles compared with a calcium phosphate procedure. The DNA concentration, distance between the discharge chamber and the retaining screen and the vacuum in the apparatus also influenced gene delivery. Sections prepared for light and electron microscopy showed the localisation, within target cells, of gold particles used to deliver the DNA. Immunolocalization of foreign gene expression within cells confirmed an even distribution of gene product throughout the cell cytoplasm.

Regulation of Nuclear Transport in Proliferating and Quiescent Cells

Previously, we compared signal-mediated nuclear transport in proliferating and quiescent BALB/c 3T3 cells and found that both the relative rate of nuclear uptake and the functional size of the transport channels were significantly greater in proliferating cells. In this study, the possible causes of these permeability differences were investigated. To determine if the decrease in transport capacity in quiescent cells was due to a reduction in the availability of soluble cytoplasmic factors (i.e., ATP or receptors for nuclear location sequences), or changes in the properties of the pores themselves, proliferating and quiescent cells were fused, and nuclear import of nucleoplasmin-coated gold (NP-gold) particles was assayed in the heterokaryons 50-60 min later. Significant differences in nuclear uptake were maintained following fusion, even though the two nuclei shared a common cytoplasm, consistent with the view that permeability is regulated at the level of the pores. Cell shape also influenced signal-mediated nuclear import. This was demonstrated by studying transport in rounded and flattened cells attached to different-size palladium domains that were deposited on a nonadhesive substrate. Based on analysis of the nuclear uptake rates of large (110-270 Å in diameter) and small (50-80 Å in diameter) coated gold particles, it was determined that the functional size of the pores was significantly greater in flattened cells. The effect of growth factors on recovery of nuclear transport capacity following serum depletion was also analyzed. Partial recovery was achieved by treating cells with physiological concentrations of EGF, IGF-1, or PDGF; however, complete recovery required both EGF and IGF-1.

Participation of d-galactose-specific receptors of liver macrophages in recognition of fibronectin-opsonized particles

The interaction of immobilized human or rat plasma fibronectin with isolated rat liver macrophages was studied in a model system using colloidal gold of 17-nm diameter (Au-17) as test particles. Plasma fibronectin (pFn)-coated gold particles were rapidly bound and endocytosed via the coated pit-coated vesicle pathway as demonstrated by photometry, and light and electron microscopy. The isolated macrophages bind 2.5 ± 2 particles/10 μm of plasma membrane (incubation at 4°), equalling a binding capacity of ∼3.5 × 10 4 pFn-au-17 particles per cell. Binding and uptake (at 37°) was specifically inhibited by d-galactose-related carbohydrates, but not by d-mannose, N-acetyl- d-glucosamine, nor by excess soluble pFn. Uptake was also inhibited by lactosylated bovine serum albumin at a concentration of 10 −6 m but not by bovine serum albumin. India ink uptake by the liver macrophages in the presence of fibronectin was also inhibited by d-galactose-related monosaccharides. The presence of terminal, nonreducing d-galactosyl groups on pFn could be demonstrated by agglutination experiments with the d-galactose-specific plant lectin, Ricinus communis agglutinin (RCA), which could also be used for isolation of pFn from rat plasma. The 29-kDa molecular mass d-galactose-specific receptor, known to be expressed on the liver macrophage membrane and recently shown to be a membrane-bound form of C-reactive protein, was found to bind the pFn-coated gold particles in dot blotting experiments. It was concluded that the d-galactose-specific macrophage receptor binds to terminal d-galactose-related units of immobilized pFn and participates in recognition of fibronectin-opsonized particles.

Movement of a karyophilic protein through the nuclear pores of oocytes.

It has recently been shown that large karyophilic proteins are transported across the nuclear envelope in amphibian oocytes. In consideration of this, the present experiments were performed to identify the specific sites within the envelope through which transport occurs and determine if molecular size is a limiting factor in the transport process. The following experimental procedure was employed: Colloidal gold particles, varying in size from approximately 20 to 170 A in diameter were coated with nucleoplasmin, a 165,000-mol-wt karyophilic protein, which is known to be transported through the envelope. The coated gold particles were microinjected into the cytoplasm of Xenopus oocytes, and the cells were fixed 15 min and 1 h later. The intracellular localization of the gold was then determined with the electron microscope. It was found that nucleoplasmin-coated particles readily enter the nucleus. On the basis of the distribution of the particles associated with the envelope, we concluded that transport occurs through the nuclear pores. Furthermore, the size distributions of the gold particles present in the nucleus and cytoplasm were not significantly different, indicating that the envelope does not discriminate among particles with diameters ranging from 50 to 200 A (the dimensions including the nucleoplasmin coat). Colloidal gold coated with trypsin-digested nucleoplasmin (which lacks the polypeptide domain required for transport) or exogenous polyvinylpyrrolidone were largely excluded from the nucleus and showed no evidence of transport.