Silver Alloy Nanoparticles Research Articles

Photoluminescence enhancement of carbon dots induced by hybrids of photonic crystals and gold–silver alloy nanoparticles

A novel strategy to enhance the fluorescence intensity of orange carbon dots was obtained by synergistically manipulating an electromagnetic field through opal photonic crystals and the localized surface plasmon resonance of a metal structure.

Investigation of photophysicochemical properties of zinc phthalocyanines conjugated to metallic nanoparticles

Abstract The syntheses of zinc(II) tetra–[3–(4–phenoxy) (propanoic acid) phthalocyanine] ( 2 ) and zinc(II) mono–[3–(4–phenoxy) (propanoic acid) phthalocyanine ( 3 ) are reported in this work. Compounds 2 and 3 were covalently linked to glutathione capped silver (AgNPs–GSH), gold (AuNPs–GSH) and silver-gold alloy (Ag 3 Au 1 NPs–GSH) nanoparticles (NPs) via an amide bond formation to afford the conjugates: 2 –AgNPs–GSH, 3 –AgNPs–GSH, 2 –AuNPs–GSH, 3 –AuNPs–GSH, 2 -Ag 3 Au 1 NPs–GSH and 3 -Ag 3 Au 1 NPs–GSH. The photophysicochemical behaviours of the compounds and their conjugates with NPs were assessed in solution. The conjugates afforded a decrease in fluorescence quantum yields and lifetimes with improved triplet quantum yields in comparison to the compounds. Accordingly, the AgNPs and AuNPs conjugates with the compounds afforded high singlet quantum yields. On the contrary, the conjugates of the alloy afforded decreased singlet quantum yields probably due to the screening effect. The compounds and their conjugates with NPs could serve as a viable and efficacious photosensitizer for photodynamic therapy.

Silver and palladium alloy nanoparticle catalysts: reductive coupling of nitrobenzene through light irradiation.

Silver-palladium (Ag-Pd) alloy nanoparticles strongly absorb visible light and exhibit significantly higher photocatalytic activity compared to both pure palladium (Pd) and silver (Ag) nanoparticles. Photocatalysts of Ag-Pd alloy nanoparticles on ZrO2 and Al2O3 supports are developed to catalyze the nitroaromatic coupling to the corresponding azo compounds under visible light irradiation. Ag-Pd alloy NP/ZrO2 exhibited the highest photocatalytic activity for nitrobenzene coupling to azobenzene (yield of ∼80% in 3 hours). The photocatalytic efficiency could be optimized by altering the Ag : Pd ratio of the alloy nanoparticles, irradiation light intensity, temperature and wavelength. The rate of the reaction depends on the population and energy of the excited electrons, which can be improved by increasing the light intensity or by using a shorter wavelength. The knowledge developed in this study may inspire further studies on Ag alloy photocatalysts and organic syntheses using Ag-Pd nanoparticle catalysts driven under visible light Irradiation.

Electrospun Polyaniline-Based Composite Nanofibers: Tuning the Electrical Conductivity by Tailoring the Structure of Thiol-Protected Metal Nanoparticles

Composite nanofibers made of a polyaniline-based polymer blend and different thiol-capped metal nanoparticles were prepared using ex situ synthesis and electrospinning technique. The effects of the nanoparticle composition and chemical structure on the electrical properties of the nanocomposites were investigated. This study confirmed that Brust’s procedure is an effective method for the synthesis of sub-10 nm silver, gold, and silver-gold alloy nanoparticles protected with different types of thiols. Electron microscopy results demonstrated that electrospinning is a valuable technique for the production of composite nanofibers with similar morphology and revealed that nanofillers are well-dispersed into the polymer matrix. X-ray diffraction tests proved the lack of a significant influence of the nanoparticle chemical structure on the polyaniline chain arrangement. However, the introduction of conductive nanofillers in the polymer matrix influences the charge transport noticeably improving electrical conductivity. The enhancement of electrical properties is mediated by the nanoparticle capping layer structure. The metal nanoparticle core composition is a key parameter, which exerted a significant influence on the conductivity of the nanocomposites. These results prove that the proposed method can be used to tune the electrical properties of nanocomposites.

Synthesis and characterization of gold – silver alloy nanoparticles

Gold–Silver alloy nanoparticles were synthesized by microwave assisted redution and polyol reactions, where trisodium citrate (TSC) and poly vinyl pyrollidone (PVP, Mn=1,000,000) played as protective agents, process includes two steps: (i) first, gold nanoparticles were synthesized, (ii) then silver nanoparticles were developed on gold nanoparticles surfaces to form alloy nanoscale. The results of the analysis from UV-Vis, XRD, TEM spectrums showed that gold – silver alloy nanoparticles mostly had core–shell structure and gold was proposed as the core. The particle size of alloy nanoparticles was 30–35 nm, and developed if the amount of silver has increased. UV-Vis spectrum showed this solution has a shoulder peak beside maximum absorbent peak. Trisodium citrate kept an important role to form gold–silver alloy nanoparticles in ethylene glycol.

A facile and green strategy for the synthesis of Au, Ag and Au-Ag alloy nanoparticles using aerial parts of R. hypocrateriformis extract and their biological evaluation.

A facile and green strategy is reported here to synthesize gold (Au), silver (Ag) and gold-silver (Au-Ag) alloy nanoparticles (NPs) through bio-reduction reactions of aqueous corresponding metal precursors mediated by extracts of aerial parts of R. hypocrateriformis, which act as both reducing and stabilizing agents, under microwave irradiation. UV-vis spectrophotometer, XRD, FT-IR, FESEM/TEM, TGA and EDAX analysis were used to characterize the obtained NPs. The formation of NPs is evident from their surface plasmon resonance peak observed at λmax=∼550, 450 and 500nm for Au, Ag and Au-Ag alloy NPs respectively. XRD pattern revealed that fcc structure, while FT-IR spectra signify the presence of phytochemicals adsorbed on NPs. Such a biofunctionalized NPs were characterized by their weight loss, 30% due to thermal degradation of plant phytochemicals observed in TG analysis. The spherical shape of Au, Ag and Au-Ag alloy NPs (∼10-50nm) is observed by FE-SEM/TEM images. EDAX analysis confirms the expected elemental composition. Moreover, these NPs showed enhanced antimicrobial, antioxidant, and anticancer activities, though it is more pronounced for Au-Ag alloy NPs, which is due to the combining effect of phytochemicals, Au and Ag metals. Thus, the biosynthesized NPs could be applied as effective growth inhibitors for various biomedical applications.

Electrochemical Behavior of Gold–Silver Alloy Nanoparticles

AbstractWe report the voltammetry of alloy nanoparticles by using cyclic voltammetry to study gold–silver alloy nanoparticles. Through careful comparison with the response of pure gold nanoparticles, pure silver nanoparticles, and their mixture, the contrasting electrochemical behavior of the alloy nanoparticles is established, providing insights into the electrochemical stability of gold–silver alloy nanoparticles in chloride‐containing media.

Kolanut (Cola nitida) Mediated Synthesis of Silver–Gold Alloy Nanoparticles: Antifungal, Catalytic, Larvicidal and Thrombolytic Applications

This study investigated use of leaf, seed, seed shell and pod extracts of Cola nitida for the green synthesis of silver-alloy nanoparticles (Ag–AuNPs). The Ag–AuNPs formed were dark brown with maxima absorbance in the range of 497–531 nm. FTIR peaks at 3290–3396 and 1635–1647 cm−1 showed that proteins were the capping and stabilization molecules for the synthesis of Ag–AuNPs. While leaf, seed and seed shell extract-mediated Ag–AuNPs had near spherical morphology, anisotropic structures of sphere, rod, hexagon and triangle were formed by pod extract. The polydispersed particles were 17–91 nm in size, with crystalline characteristics and prominent presence of Ag and Au in the EDX spectra. Ag–AuNPs inhibited growth of Aspergillus flavus, A. fumigatus and A. niger by 69.51–100 %. Exposure of Anopheles mosquito larvae to Ag–AuNPs resulted in 80–100 % mortality in 24 h. Catalytic degradation of >90 and >60 % were obtained for malachite green and methylene blue respectively after 24 h. The particles displayed potent blood anticoagulant and thrombolytic activities, indicative of their potentials in the management blood coagulation disorders. This study showed that C. nitida can be used for green synthesis of Ag–AuNPs, which is the first report of its kind.

Broadband optical absorption enhancement of N719 dye in ethanol by gold–silver alloy nanoparticles fabricated under laser ablation technique

The formation of gold–silver alloy nanoparticles (Au–Ag alloy NPs) by a two-step process with a pulsed Nd:YAG laser without any additives is presented. Mixtures of Au and Ag colloidal suspensions were separately obtained by 1064-nm laser ablation of metallic targets immersed in ethanol. Subsequently, the as-mixed colloidal suspensions were reirradiated by laser-induced heating at the second-harmonic generation (532 nm) for different irradiation periods of time. The absorption spectra and morphology of the colloidal alloys were studied as a function of exposure time to laser irradiation. Transmission electron microscopy revealed the formation of monodispersed spherical nanoparticles with a homogeneous size distribution in all the synthesized samples. UV–vis and photoluminescence spectroscopy measurements were also employed to characterize the changes in the light absorption and emission of N719 dye solution with different concentrations of Au–Ag colloidal alloys, respectively. The localized surface plasmon resonance (LSPR) of Au–Ag alloy NPs enhanced the absorption and fluorescence peak of the dye solution. The mixture of dye molecules with a higher concentration of alloy NPs exhibited an additional coupling of dipole moments with the LSPR, thereby contributing to the improvement of the optical properties of the mixture.

Preparation of gold and gold–silver alloy nanoparticles for enhancement of plasmonic dye-sensitized solar cells performance

A two-step method was applied to obtain gold–silver alloy nanoparticles (Au–Ag alloy NPs). First, Au and Ag colloids with average particle sizes of 14.80 and 8.47nm, respectively, were synthesized by pulsed laser ablation of pure metallic targets immersed in ethanol, subsequent mixing, and re-irradiation of individual Au and Ag colloids (volume ratio of 4:1). In this study, a dense layer of porous titanium dioxide (TiO2) film with a thickness of ∼11μm was deposited directly on the central area of the conductive face of a fluorine tin oxide (FTO) glass by blade doctor method. A specific amount of N719 dye molecules with and without the plasmonic-metal nanoparticles (NPs) was mixed, incorporated into the porous TiO2 film, and used as photoanode to fabricate dye-sensitized solar cells (DSSCs). The optical and structural properties of the prepared photoanodes before their application to DSSCs were investigated. The photocurrent density–voltage and external quantum efficiency characteristics of the DSSCs fabricated with these photoanodes were also analyzed and discussed. The experimental results confirmed the plasmonic enhancement effects on the performance of DSSCs, which indicated that cells loaded with the plasmonic-metal NPs yielded larger enhancement. The plasmonic effect of the Au–Ag alloy NPs significantly enhanced the broadband light absorption of dye molecules. The best cell was achieved using the photoanode loaded with Au–Ag alloy NPs, exhibiting a power conversion efficiency of 5.81%, which was ∼8.4% and 52.1% higher than that of the DSSCs with Au NPs and the reference cell, respectively.

Gold silver alloy nanoparticles (GSAN): an imaging probe for breast cancer screening with dual-energy mammography or computed tomography.

Earlier detection of breast cancer reduces mortality from this disease. As a result, the development of better screening techniques is a topic of intense interest. Contrast-enhanced dual-energy mammography (DEM) is a novel technique that has improved sensitivity for cancer detection. However, the development of contrast agents for this technique is in its infancy. We herein report gold-silver alloy nanoparticles (GSAN) that have potent DEM contrast properties and improved biocompatibility. GSAN formulations containing a range of gold : silver ratios and capped with m-PEG were synthesized and characterized using various analytical methods. DEM and computed tomography (CT) phantom imaging showed that GSAN produced robust contrast that was comparable to silver alone. Cell viability, reactive oxygen species generation and DNA damage results revealed that the formulations with 30% or higher gold content are cytocompatible to Hep G2 and J774A.1 cells. In vivo imaging was performed in mice with and without breast tumors. The results showed that GSAN produce strong DEM and CT contrast and accumulated in tumors. Furthermore, both in vivo imaging and ex vivo analysis indicated the excretion of GSAN via both urine and feces. In summary, GSAN produce strong DEM and CT contrast, and has potential for both blood pool imaging and for breast cancer screening.

Analysis of Photoacoustic Response from Gold–Silver Alloy Nanoparticles Irradiated by Short Pulsed Laser in Water

We perform a finite element-based numerical analysis to calculate the photoacoustic (PA) signal generated by spherical gold–silver (Au–Ag) alloy nanoparticles (NPs). These spherical particles are size-controlled and monodispersed, with tunable plasmonic resonance wavelength via change of the alloy composition. This enables their use in PA imaging as a contrast agent. This theoretical framework self-consistently solves the electromagnetic, thermodynamic and transient acoustic pressure physics using a multiphysics coupling approach. We model our system as an optically heterogeneous medium irradiated by a nanosecond laser pulse in the tissue therapeutic optical window (NIR irradiation, with wavelength of 800 nm). We calculate the PA signal generated by the photothermal expansion of both the particle and its surrounding medium. The results show the impact of the gold molar fraction (GMF) of Au–Ag alloy NPs on the PA signal for different NP sizes. We show that significantly stronger PA signals are achieved usi...

Investigation of bimetallic nanoparticles with broad plasmon response

Gold–silver bimetallic nanoparticles with broad plasmon response were fabricated on soft substrates using a laser-induced transfer technique. The bimetallic nanostructures were fabricated with centimeter scale. By careful design, an approximately 200-nm broad plasmon response can be obtained by gold–silver alloy nanoparticles, which can be attributed to the electromagnetic interaction between gold and silver nanoparticles. This nanofabrication technique provides an annealing-free approach for the fabrication of flexible bimetallic nanostructures with a broad plasmon response with low cost.

Seeded Growth Synthesis of Composition and Size-Controlled Gold–Silver Alloy Nanoparticles

We propose a novel methodology to synthesize monodisperse gold–silver alloy nanoparticles (NPs) with fine control of size and composition. The synthesis is based on a combination of the coreduction of gold and silver salts for the formation of alloys and the seeded growth approach for the formation of size-controlled NPs. While the simple use of coreduction gives alloy NPs limited to ∼30 nm, the combination of both methods yields spherical alloy NPs with a size that can be controlled between ∼30 and ∼150 nm, with a coefficient of variation smaller than 15%. The alloy NPs can be synthesized to any composition between pure silver and pure gold. We also show that the alloy composition is nonhomogeneous, with a gold-rich core and a silver-rich surface. The transition in the alloy composition is gradual from the core to the surface, resulting in optical properties very similar to the optical properties of a homogeneous alloy, except for the smaller (∼30 nm) NPs. A multilayer Mie model has been introduced to st...

Toxicity of silver and gold nanoparticles on marine microalgae

The increased use of nanomaterials in several novel industrial applications during the last decade has led to a rise in concerns about the potential toxic effects of released engineered nanoparticles (NPs) into the environment, as their potential toxicity to aquatic organisms is just beginning to be recognised. Toxicity of metallic nanoparticles to aquatic organisms, including microalgae, seems to be related to their physical and chemical properties, as well as their behaviour in the aquatic media where processes of dissolution, aggregation and agglomeration can occur. Although the production of these particles has increased considerably in recent years, data on their toxicity on microalgae, especially those belonging to marine or estuarine environments remain scarce and scattered. The literature shows a wide variation of results on toxicity, mainly due to the different methodology used in bioassays involving microalgae. These can range for up to EC50 data, in the case of AgNPs, representing five orders of magnitude. The importance of initial cellular density is also addressed in the text, as well as the need for keeping test conditions as close as possible to environmental conditions, in order to increase their environmental relevance. This review focuses on the fate and toxicity of silver, gold, and gold–silver alloy nanoparticles on microalgae, as key organisms in aquatic ecosystems. It is prompted by their increased production and use, and taking into account that oceans and estuaries are the final sink for those NPs. The design of bioassays and further research in the field of microalgae nanoecotoxicology is discussed, with a brief survey on newly developed technology of green (algae mediated) production of Ag, Au and Ag–Au bimetallic NPs, as well as some final considerations about future research on this field.

Influence of gold, silver and gold-silver alloy nanoparticles on germ cell function and embryo development.

The use of engineered nanoparticles has risen exponentially over the last decade. Applications are manifold and include utilisation in industrial goods as well as medical and consumer products. Gold and silver nanoparticles play an important role in the current increase of nanoparticle usage. However, our understanding concerning possible side effects of this increased exposure to particles, which are frequently in the same size regime as medium sized biomolecules and accessorily possess highly active surfaces, is still incomplete. That particularly applies to reproductive aspects, were defects can be passed onto following generations. This review gives a brief overview of the most recent findings concerning reprotoxicological effects. The here presented data elucidate how composition, size and surface modification of nanoparticles influence viablility and functionality of reproduction relevant cells derived from various animal models. While in vitro cultured embryos displayed no toxic effects after the microinjection of gold and silver nanoparticles, sperm fertility parameters deteriorated after co-incubation with ligand free gold nanoparticles. However, the effect could be alleviated by bio-coating the nanoparticles, which even applies to silver and silver-rich alloy nanoparticles. The most sensitive test system appeared to be in vitro oocyte maturation showing a dose-dependent response towards protein (BSA) coated gold–silver alloy and silver nanoparticles leading up to complete arrest of maturation. Recent biodistribution studies confirmed that nanoparticles gain access to the ovaries and also penetrate the blood–testis and placental barrier. Thus, the design of nanoparticles with increased biosafety is highly relevant for biomedical applications.

Spherically-clustered porous Au-Ag alloy nanoparticle prepared by partial inhibition of galvanic replacement and its application for efficient multimodal therapy.

The polyvinylpyrrolidone (PVP)-coated spherically clustered porous gold-silver alloy nanoparticle (PVP-SPAN) was prepared by low temperature mediated, partially inhibited galvanic replacement reaction followed by silver etching process. The prepared porous nanostructures exhibited excellent photothermal conversion efficiency under irradiation of near-infrared light (NIR) and allowed a high payload of both doxorubicin (Dox) and thiolated dye-labeled oligonucleotide, DNAzyme (FDz). Especially, PVP-SPAN provided 10 times higher loading capacity for oligonucleotide than conventional hollow nanoshells due to increased pore diameter and surface-to-volume ratio. We demonstrated highly efficient chemo-thermo-gene multitherapy based on codelivery of Dox and FDz with NIR-mediated photothermal therapeutic effect using a model system of hepatitis C virus infected human liver cells (Huh7 human hepatocarcinoma cell line containing hepatitis C virus NS3 gene replicon) compared to conventional hollow nanoshells.

Room temperature benzaldehyde oxidation using air over gold–silver nanoalloy catalysts

In this study gold–silver alloy nanoparticles were prepared by chemical reduction method using silver nitrate and chloroauric acid as metal precursor, cetyl trimethyl ammonium bromide as protecting agent and sodium borohydride (NaBH4) as a reducing agent. Formation of alloy nanoparticles was monitored using UV–vis absorption spectroscopy and dynamic light scattering (DLS). Stability of alloy nanoparticles was detected by turbiscan. Gold–silver alloy nanoparticles were supported on silica by dispersing silica powder in the suspension of destabilized nanoparticles. Ag–Au/SiO2 samples were characterized by UV–vis absorption spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N2 adsorption–desorption and inductively coupled plasma-optical emission spectroscopy (ICP-OES). The catalysts were tested for the liquid phase oxidation of benzaldehyde (BZ) affording high selectivity to methyl benzoate (MB) as compared to the catalyst prepared by the conventional reported methods. The oxidation of benzaldehyde was subjected to detailed investigations to study the effect of parameters such as time, temperature, amount and different concentration of catalysts, amount of benzaldehyde and concentration of the base. Catalyst containing 1.5 wt% Au–1.5 wt% Ag exhibited the best catalytic performance in benzaldehyde oxidation in the presence of methanol as solvent. The used catalyst was recycled to four cycles without significant loss in its activity.

Synthesis and optical properties of colloidal Au-Ag alloy nanoparticles

Colloidal gold–silver alloy nanoparticles (NPs) of variable composition were synthesised by sodium citrate reduction of mixed metal precursors at low concentrations. Scanning electron micrograph (SEM) images showed presence of particles in the 10–70 nm diameter range depending on the alloy compositions. A single surface plasmon resonance (SPR) peak observed in the visible spectrum proved the formation of homogeneous gold–silver alloy NPs. The position of the SPR absorption band maximum increased linearly with increasing gold content in the alloy NPs, ranging from 406 nm to 526 nm. No signicant change in surface plasmon bands was observed for fresh samples and after three months at room temperature indicating fair stability of the particles. Some alloy NPs show fluorescence emission peaks with blue and red shifts compared with the observed fluorescence from pure gold NPs.

Study on metal nanoparticles synthesis and orientation of gemini surfactant molecules used as stabilizer

In the present study, we report the synthesis of gold (Au), silver (Ag), and gold–silver alloy (Au–Ag) nanoparticles (NPs) by seed-mediated method using gemini surfactant, containing diethyl ether spacer group as a stabilizer. As-synthesized NPs are found very much stable and have been characterized using UV–vis spectroscopy, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and zeta potential techniques. The orientation of gemini surfactant molecules surrounding the metal NPs has been investigated exploiting twisted intramolecular charge transfer (TICT) fluorescence properties of a probe 4-(N,N-dimethylamino) cinnamaldehyde (DMACA). The quenching efficiencies of different NPs have been performed in the fluorescence of DMACA and are found to be different. This effect can be related to the location of DMACA as well as the electro-negativity of the metals as the extent of orientation of the surfactant molecules around NPs controls the location of DMACA in a bilayer. To support the location of DMACA, fluorescence quenching studies with cetylpyridinium chloride (CPC) as an external quencher have also been carried out.