Gold Alloy Nanoparticles Research Articles

Reprotoxicity of gold, silver, and gold–silver alloy nanoparticles on mammalian gametes

Metal and alloy nanoparticles are increasingly developed for biomedical applications, while a firm understanding of their biocompatibility is still missing. Various properties have been reported to influence the toxic potential of nanoparticles. This study aimed to assess the impact of nanoparticle size, surface ligands and chemical composition of gold, silver or gold-silver alloy nanoparticles on mammalian gametes. An in vitro assay for porcine gametes was developed, since these are delicate primary cells, for which well-established culture systems exist and functional parameters are defined. During coincubation with oocytes for 46 h neither any of the tested gold nanoparticles nor the gold-silver alloy particles with a silver molar fraction of up to 50% showed any impact on oocyte maturation. Alloy nanoparticles with 80% silver molar fraction and pure silver nanoparticles inhibited cumulus-oocyte maturation. Confocal microscopy revealed a selective uptake of gold nanoparticles by oocytes, while silver and alloy particles mainly accumulated in the cumulus cell layer surrounding the oocyte. Interestingly sperm vitality parameters (motility, membrane integrity and morphology) were not affected by any of the tested nanoparticles. Only sporadic association of nanoparticles with the sperm plasma membrane was found by transmission electron microscopy. In conclusion, mammalian oocytes were sensitive to silver containing nanoparticles. Likely, the delicate process of completing meiosis in maternal gametes features high vulnerability towards nanomaterial derived toxicity. The results imply that released Ag(+)-ions are responsible for the observed toxicity, but the compounding into an alloy seemed to alleviate the toxic effects to a certain extent.

Charge Doping of Large-Area Graphene by Gold-Alloy Nanoparticles

We present a facile, one-step, and surfactant-free method for direct synthesis and loading of stable gold and gold-alloy nanoparticles (NPs) on large-area graphene using an electrical discharge in a liquid environment, termed solution plasma. We observed a charge doping of graphene by the gold NPs, which depends on the particles’ chemical composition, even if the NPs contain a few percent of trivalent sp metals, such as indium (In) or gallium (Ga). Raman and electron energy loss spectroscopy (EELS) methods show that graphene is doped with electrons (n-type) in the case of gold NPs and with holes (p-type) in the case of gold-alloy NPs. The Raman band shift indicates that the amount of the transferred electrons from the gold NPs to graphene is −2 × 10–4 electrons per unit cell. The gold-alloy NPs receive from graphene (2 and 4) × 10–5 electrons per unit cell if the gold NPs contain In and Ga, respectively. In the EELS spectra, the decrease in the intensity of the 1s-π* transition and the shift of the π* pea...

Alloying colloidal silver nanoparticles with gold disproportionally controls antibacterial and toxic effects

Elemental silver nanoparticles are an effective antibacterial substance and are found as additive in various medical applications. Gold nanoparticles are used due to their optical properties in microscopy and cancer therapy. These advantages might be combined within alloyed nanoparticles of both elements and thereby open new fields of interest in research and medical treatment. In this context, laser ablation of solid alloys in liquid gives access to colloidal silver–gold alloy nanoparticles with a homogeneous ultrastructure. Elemental and alloy silver–gold nanoparticles with increasing molar fractions of silver (50, 80, and 100 %) were produced and stabilized with citrate or albumin (BSA). Particles were embedded in agar at concentrations of 3–100 μg cm−3 and tested on clinical relevant Staphylococcus aureus regarding their antibacterial properties. Cytotoxic effects were measured within the same particle concentration range using human gingival fibroblasts (HGFib). As expected, a reduced fraction of silver in the nanoalloys decreased the antibacterial effect on S. aureus according to the evaluated minimal inhibitory concentrations. However, this decrease turned out stronger than expected by its relative mass per particle, due to the electrochemical, disproportionally high effect of gold on the bioresponse to silver within silver–gold nanoalloy particles. BSA was able to stabilize all colloids and maintain antibacterial activity, whereas sodium citrate reduced antibacterial effects and cytotoxicity even at high nanoparticle concentrations. The alloying of silver with gold by laser ablation in liquid produced nanoparticles with both reduced antibacterial and cytotoxic properties in comparison to silver nanoparticles but still retains the application spectrum of both elements combined in one colloid. In particular, alloying with gold may render silver nanoparticles more biocompatible, and allows bioconjugation via established thiol chemistry.

Enhancing Catalytic Performance of Palladium in Gold and Palladium Alloy Nanoparticles for Organic Synthesis Reactions through Visible Light Irradiation at Ambient Temperatures

The intrinsic catalytic activity of palladium (Pd) is significantly enhanced in gold (Au)-Pd alloy nanoparticles (NPs) under visible light irradiation at ambient temperatures. The alloy NPs strongly absorb light and efficiently enhance the conversion of several reactions, including Suzuki-Miyaura cross coupling, oxidative addition of benzylamine, selective oxidation of aromatic alcohols to corresponding aldehydes and ketones, and phenol oxidation. The Au/Pd molar ratio of the alloy NPs has an important impact on performance of the catalysts since it determines both the electronic heterogeneity and the distribution of Pd sites at the NP surface, with these two factors playing key roles in the catalytic activity. Irradiating with light produces an even more profound enhancement in the catalytic performance of the NPs. For example, the best conversion rate achieved thermally at 30 °C for Suzuki-Miyaura cross coupling was 37% at a Au/Pd ratio of 1:1.86, while under light illumination the yield increased to 96% under the same conditions. The catalytic activity of the alloy NPs depends on the intensity and wavelength of incident light. Light absorption due to the Localized Surface Plasmon Resonance of gold nanocrystals plays an important role in enhancing catalyst performance. We believe that the conduction electrons of the NPs gain the light absorbed energy producing energetic electrons at the surface Pd sites, which enhances the sites' intrinsic catalytic ability. These findings provide useful guidelines for designing efficient catalysts composed of alloys of a plasmonic metal and a catalytically active transition metal for various organic syntheses driven by sunlight.

EPR-effect: Utilizing size-dependent Nanoparticle Delivery to Solid Tumors

EPR-effect: Utilizing size-dependent Nanoparticle Delivery to Solid Tumors

Resonant light scattering spectroscopy of gold, silver and gold–silver alloy nanoparticles and optical detection in microfluidic channels

Dark field resonant light scattering by gold and silver nanoparticles enables the detection and spectroscopy of such particles with high sensitivity, down to the single-particle level, and can be used to implement miniaturised optical detection schemes for chemical and biological analysis. Here, we present a straightforward optical spectroscopic methodology for the quantitative spectrometric study of resonant light scattering (RLS) by nanoparticles. RLS spectroscopy is complementary to UV-visible absorbance measurements, and we apply it to the characterisation and comparison of different types of gold, silver and gold-silver alloy nanoparticles. The potential of gold and silver particles as alternatives for fluorescent probes in certain applications is discussed. RLS spectroscopy is shown to be useful for studying analyte-induced gold nanoparticle assembly and nanoparticle chemistry, which can induce radical changes in the plasmonic resonances responsible for the strong light scattering. Furthermore, the feasibility of dark field RLS detection and quantitation of metal nanoparticles in microfluidic volumes is demonstrated, opening interesting possibilities for the further development of microfluidic detection schemes.

Silver, gold, and alloyed silver–gold nanoparticles: characterization and comparative cell-biologic action

Silver, gold, and silver–gold-alloy nanoparticles were prepared by citrate reduction modified by the addition of tannin during the synthesis, leading to a reduction in particle size by a factor of three. Nanoparticles can be prepared by this easy water-based synthesis and subsequently functionalized by the addition of either tris(3-sulfonatophenyl)phosphine or poly(N-vinylpyrrolidone). The resulting nanoparticles of silver (diameter 15–25 nm), gold (5–6 nm), and silver–gold (50:50; 10–12 nm) were easily dispersable in water and also in cell culture media (RPMI + 10 % fetal calf serum), as shown by nanoparticle tracking analysis and differential centrifugal sedimentation. High-resolution transmission electron microscopy showed a polycrystalline nature of all nanoparticles. EDX on single silver–gold nanoparticles indicated that the concentration of gold is higher inside a nanoparticle. The biologic action of the nanoparticles toward human mesenchymal stem cells (hMSC) was different: Silver nanoparticles showed a significant concentration-dependent influence on the viability of hMSC. Gold nanoparticles showed only a small effect on the viability of hMSC after 7 days. Surprisingly, silver–gold nanoparticles had no significant influence on the viability of hMSC despite the silver content. Silver nanoparticles and silver–gold nanoparticles in the concentration range of 5–20 μg mL−1 induced the activation of hMSC as indicated by the release of IL-8. In contrast, gold nanoparticles led to a reduction of the release of IL-6 and IL-8.

A Visualized Assay for Quercetin Based on the Formation of Silver–Gold Alloy Nanoparticles

A visualized assay for quercetin (QU) was first developed based on the formation of silver–gold alloy nanoparticles in this contribution. With the ability to reduce metal ions to metal substances, QU could reduce Ag+ absorbed on the surface of gold nanoparticles to metallic silver. The thickness of the formed Ag shell and the color change of the solution were proportional to the concentration of QU. Therefore, visualized detection of QU could be realized by studying the surface resonance plasmon absorption spectra of the analytical systems after addition of different concentration of QU. Under optimum conditions, trace amount of QU could be detected in the linear range 9.0 × 10−7–1.0 × 10−4 mol L−1 with a detection limit of 6.5 × 10−7 mol L−1. The present assay was applied in the determination of QU in human serum and satisfactory results were obtained. This assay is simple, rapid, and cost-effective, and it is a powerful complement for the spectroscopy assays for QU. Also, it is the first visualized spectroscopic assay of QU until now.

Catalytic activity of nanoalloys from gold and palladium

We present a quantitative study of the catalytic activity of well-defined faceted gold-palladium nanoalloys which are immobilized on cationic spherical polyelectrolyte brushes. The spherical polyelectrolyte brush particles used as carriers for the nanoalloys consist of a solid polystyrene core onto which cationic polyelectrolyte chains of 2-aminoethyl methacrylate are attached. Au/Pd nanoalloy particles with sizes in the range from 1 to 3 nm have been generated which are homogeneously distributed on the surface of the spherical polyelectrolyte brushes. The reduction of 4-nitrophenol has been chosen as a well-controlled model reaction allowing us to determine the catalytic activity of the nanoalloys as a function of the Au/Pd composition. The adsorption behavior was studied by Langmuir-Hinshelwood kinetics. We find a pronounced maximum of the catalytic activity at 75 molar % Au. A comparison of gold, platinum, palladium and gold-palladium alloy nanoparticles is made in terms of Langmuir-Hinshelwood kinetics. Density functional calculations for Au/Pd clusters with up to 38 atoms show that the density of states at the Fermi level increases with increasing Pd content, and that the highest occupied orbitals are associated with Pd atoms. The calculations confirm that small changes in the atomic arrangement can lead to pronounced changes in the particles' electronic properties, indicating that the known importance of surface effects is further enhanced in nanoalloys.

Highly stable Pt monolayer on PdAu nanoparticle electrocatalysts for the oxygen reduction reaction

Stability is one of the main requirements for commercializing fuel cell electrocatalysts for automotive applications. Platinum is the best-known catalyst for oxygen reduction in cathodes, but it undergoes dissolution during potential changes while driving electric vehicles, thus hampering commercial adoption. Here we report a new class of highly stable, active electrocatalysts comprising platinum monolayers on palladium-gold alloy nanoparticles. In fuel-cell tests, this electrocatalyst with its ultra-low platinum content showed minimal degradation in activity over 100,000 cycles between potentials 0.6 and 1.0 V. Under more severe conditions with a potential range of 0.6-1.4 V, again we registered no marked losses in platinum and gold despite the dissolution of palladium. These data coupled with theoretical analyses demonstrated that adding a small amount of gold to palladium and forming highly uniform nanoparticle cores make the platinum monolayer electrocatalyst significantly tolerant and very promising for the automotive application of fuel cells.

Platinum–gold alloy nanoparticles and horseradish peroxidase functionalized nanocomposite as a trace label for ultrasensitive electrochemical detection of thrombin

A novel tracer, platinum–gold alloy nanoparticles (Pt–AuNPs) and horseradish peroxidase (HRP) functionalized single-walled carbon nanotubes (SWCNTs) composite, is employed to label the secondary thrombin aptamer for constructing an ultrasensitive electrochemical aptasensor. Thionine, immobilized on functionalized SWCNTs, provides a pair of distinguished redox peak for electrochemical detection. Both the high-content Pt–AuNPs and HRP on SWCNTs amplify the electrochemical signal of thionine through electrocatalytic reduction of H 2O 2. Differential pulse voltammetry (DPV) is employed to detect thrombin with different concentrations. The reduction peak current is logarithmically related to the concentration of thrombin in an extremely wide range from 10 fM to 5 nM with a detection limit of 3.6 fM. The dual signal amplification of Pt–AuNPs and HRP functionalized nanocomposite provides a promising way for ultrasensitive assay in electrochemical aptasensors.

Understanding the effect of thermal treatments on the structure of CuAu/SiO2 catalysts and their performance in propene oxidation

The synthesis and catalytic application of supported CuAu is discussed. Different thermal treatments of a dried precursor of copper nitrate and tetrachloroauric acid on silica lead to catalysts with significantly different structures and properties. Direct calcination gives a catalyst which contains very large gold ensembles with minimal interaction with the copper present. Hydrogen reduction of the dried precursor leads to the formation of copper–gold alloy nanoparticles. Subsequent high temperature calcination de-alloys the copper from the gold to a significant extent. The presence of gold stabilises the formation of Cu+ on this catalyst. The activity and selectivity observed in the oxidation of propene with molecular oxygen, with or without co-fed hydrogen, depends on the pre-treatment, reaction conditions and the ratio of copper to gold in the catalyst. A number of different catalytic active sites are identified and discussed.

UV-Vis plasmon studies of metal nanoparticles

Previous studies of the surface plasmon resonance (SPR) from alloy nanoparticles of gold and silver have focused on bulk studies of the nanoparticles in solution. Here, we present a selection of data observed from individual alloy nanoparticles using highly spatially resolved electron energy-loss spectroscopy (EELS). In order to resolve the SPR in both the pure gold and Au-Ag alloy nanoparticles, we successfully applied the Richardson-Lucy deconvolution routine. We found that resonances observed from different sized alloy nanoparticles do not follow the same trends in frequency variation as their pure metal equivalent. Additionally, we do not consistently observe a single SPR peak, as one might expect from an alloy nanoparticle. This indicates that alloy nanoparticles, produced by the simultaneous reduction of metal salts, cannot be considered truly homogeneous.

Optical Absorption Properties of Dispersed Gold and Silver Alloy Nanoparticles

The oldest topic in nanoscience is the size-dependent optical properties of gold and silver colloids or nanoparticles, first investigated scientifically by Michael Faraday in 1857. In the modern era, advances in both synthesis and characterization have resulted in new insights into the size-dependent absorbance of Au and Ag nanoparticles with sizes below the classical limit for Mie theory. In this paper we discuss the synthesis and properties of core/shell and nanoalloy particles of Au and Ag, compare them to particles of pure gold and silver, and discuss how alloying affects nanoparticle chemical stability. We show that composition, size, and nanostructure (e.g., core/shell vs quasi-random nanoalloy) can all be employed to adjust the optical absorbance properties. The type of nanostructure--core/shell vs alloy--is reflected in their optical absorbance features.

In Situ Phase Separation of NiAu Alloy Nanoparticles for Preparing Highly Active Au/NiO CO Oxidation Catalysts

Multifunctional catalysts: Nickel–gold alloy nanoparticles (NPs) are synthesized in solution, by means of a fast butyllithium reduction method, and then used to prepare NiO-stabilized Au NP catalysts through a phase-transformation process (see scheme). The silica-supported catalysts exhibit a remarkable resistance to sintering and are highly active for CO oxidation.

Synthesis of Water-Soluble Iron−Gold Alloy Nanoparticles

In this study, a synthetic method to produce water-soluble iron−gold (Fe−Au) alloy nanoparticles is described. The diameter of the alloy nanoparticles is 4.9 ± 1.0 and 3.8 ± 1.0 nm for two different precursors of iron, ferrous sulfate heptahydrate (Fe2+) and iron pentacarbonyl (Fe0). The X-ray powder diffraction of the alloyed nanoparticles shows an appreciable shift in 2θ peak positions relative to pure gold or iron. Using Vegard’s law, we estimated the particle’s iron content to be 14.8 ± 4.7 mol %. The lattice constant of the alloy nanoparticles is found to be 4.0449 ± 0.0375 A. The high-resolution transmission electron microscopy images show the presence of icosahedral structures in agreement with the previous high temperature synthesis of the Fe−Au alloy nanoparticles. The optical absorption of the alloy nanoparticles is distinctive from pure gold nanoparticles and shows a relatively narrow absorption band in the range of 642−662 nm depending upon the amount of gold precursor used.

Precious metals: nanotechnology provides a new dimension

Functionalization of nanoscale (<100 nm) particles at the cellular level is highly specific and can be employed to develop efficient diagnostic and therapeutic procedures with the minimum of side effects. The binding of nanosized particles (quantum dots, iron oxide nanocrystals, nanowires, and nanotubes) with ligands creates varied optical, magnetic, or structural properties through a multivalency effect. These properties determine the affinity and specificity of nanoparticles. Several nanoparticles have been used in biomedicine such as gold, iron oxide, silver, carbon nanotubes, graphene, zinc oxide, alumina, silica, and titanium. Metallic nanoparticles (silver, gold, and silver–gold alloy nanoparticles) with their unique properties play a significant role in the prevention of blood clot formation, dissolution of blood clots, and enhanced imaging of thrombus (blood clot) in vivo. Blood is the biological fluid that delivers nanoparticles to targeted sites. Nanoparticles come in direct contact with all components of the blood, that is, erythrocytes, platelets, and leukocytes. They induce phosphatidylserine on erythrocyte membranes which alter the hemorheological mechanisms. The shape and size of RBCs are particularly important for the efficient transport of oxygen. Furthermore, deformed RBCs can be detected by the elasticity of red blood cells. In this chapter, the focus is on various applications of nanotechnology in biological systems and medicine.

Template free synthesis of silver–gold alloy nanoparticles and cellular uptake of gold nanoparticles in Chinese Hamster Ovary cell

Gold–silver alloy nanoparticles were synthesized by simultaneous reduction of varying mole fractions of HAuCl4 and AgNO3 by sodium citrate in aqueous solution without using stabilizing agents such as surfactant or polymer. Appearance of single absorption peak in visible spectrum indicated formation of homogeneous gold–silver alloy nanoparticles. Transmission electron micrographs also support formation of alloy nanoparticles rather than core–shell particles. The plasmon absorption bands for Au–Ag nanoparticles show linear bathochromic shift with increasing Au content. No significant change in surface plasmon band was observed on storage of samples at 25±2°C for 6 months, indicating stability of the particles. Particle size distribution, zeta-potential and conduction of these colloidal suspensions were measured by dynamic light scattering along with Zetasizer. Gold and Au–Ag alloy nanoparticles exhibited fluorescence at 600nm and in between 600 and 486nm respectively depending on alloy composition. Gold nanoparticles were used for cell line study using liposome as a carrier. This liposome entrapped gold nanoparticles showed enhanced uptake by Chinese Hamster Ovary (CHO) cells compared to gold nanoparticles.

Preparation of Silver - Gold Alloy Nanoparticles at Higher Concentration Using Sodium Dodecyl Sulfate

Highly stable gold–silver alloy nanoparticles with varying mole fractions were prepared in aqueous sodium dodecyl sulfate solution by simultaneous reduction of chloroauric acid (HAuCl4) and silver nitrate (AgNO3) using sodium citrate. The formation of alloy nanoparticles was confirmed by UV-visible spectroscopy and transmission electron microscopy. Particle size distribution was measured by dynamic light scattering. The surface plasmon absorption band of the Au–Ag alloy nanoparticles shows linear bathochromic shift with increasing Au content. Appearance of a single absorption peak in the visible region and lack of apparent core-shell structures in the transmission electron microscope images confirm the formation of homogeneous gold–silver alloy nanoparticles.

Preparation of silver, gold and silver–gold bimetallic nanoparticles in w/o microemulsion containing TritonX-100

Silver, gold and silver–gold alloy nanoparticles were prepared in w/o microemulsion containing TritonX-100 and cyclohexane. Silver nitrate and tetrachloroauric(III) acid (HAuCl 4) were taken as the metal precursors and sodium borohydride (NaBH 4) was used as a reducing agent. The formation of Ag and Au nanoparticles was confirmed from the appearance of surface plasmon absorption maxima at 404 ± 2 and 525 ± 2 nm for Ag and Au nanoparticles, respectively. For bimetallic nanoparticles absorption peak was observed between the two maximas of corresponding metallic particles. The surface plasmon absorption maxima for bimetallic nanoparticles changes linearly with increasing Au mole ratio content in various alloy compositions. The transmission electron microscopy (TEM) showed formation of particles of 5–50 nm diameter. Dynamic light scattering (DLS) data gave narrow particle size distribution.