Silver Alloy Nanoparticles Research Articles

Synthesis of Bimetallic Silver and Copper Alloy Nanoparticles Embedded with Styrene-Methyl Methacrylate Copolymer Nanosphere (SMMA@Ag-Cu) as a Potential Surface Enhanced Raman Scattering (SERS) Substrate

Synthesis of Bimetallic Silver and Copper Alloy Nanoparticles Embedded with Styrene-Methyl Methacrylate Copolymer Nanosphere (SMMA@Ag-Cu) as a Potential Surface Enhanced Raman Scattering (SERS) Substrate

Two-Step Synthesis of Large Gold–Silver Alloy Nanoparticles via the Combination of Seeded Growth and Citrate Co-reduction

We report a novel two-step method for the synthesis of uniform quasi-spherical and monodisperse gold–silver alloy nanoparticles with diameters of approximately 80 nm. In step one, gold–silver alloy seeds (G0) with diameters of approximately 30 nm are synthesized by citrate co-reduction of gold acetate and silver nitrate. In step two, the seeds grow into large alloy nanoparticles with diameters of approximately 80 nm by the combination of seeded growth and citrate co-reduction of gold and silver precursors. Our method makes use of gold acetate (rather than chloroauric acid) as a gold precursor to avoid the formation of silver chloride precipitates during synthesis. To our knowledge, we are the first to prepare gold–silver alloy nanoparticles with diameters of above 70 nm using gold acetate as a gold precursor. The alloy seeds and seed-grown nanoparticles show good control of size and composition, which enables tuning of the plasmonic band of these gold–silver alloy nanoparticles. Gold and silver are distributed uniformly within the cores of all Au-Ag alloy nanoparticles, while the surface is enriched in silver. This silver-enriched surface layer is thicker and more prominent for 25% Au alloy nanoparticles than for 50% and 75% Au alloy nanoparticles.

Direct Laser Writing of SERS Hollow Fibers.

We report the direct laser writing (DLW) of surface-enhanced Raman scattering (SERS) structures on the inner wall of a hollow fiber. Colloidal gold–silver alloy nanoparticles (Au–Ag ANPs) are firstly coated onto the inner wall of a hollow fiber. A green laser beam is focused through the outer surface of the hollow fiber to interact with colloidal Au–Ag ANPs so that they become melted and aggregated on the surface of the inner wall with strong adhesion. Such randomly distributed plasmonic nanostructures with high density and small gaps favor the SERS detection of low-concentration molecules in liquids flowing through the hollow fiber. Such a SERS device also supplies a three-dimensional microcavity for the interaction between excitation laser and the target molecules. The DLW system consists mainly of the flexible connection between the motor shaft and the hollow fiber, the program-controlled translation of the hollow fiber along its symmetric axis and rotation about the axis, as well as the mechanical design and the computer control system. This DLW technique enables high production, high stability, high reproducibility, high precision, and a high-flexibility fabrication of the hollow fiber SERS device. The resultant microcavity SERS scheme enables the high-sensitivity detection of R6G molecules in ethanol with a concentration of 10−7 mol/L.

Rapid visual detection for nitroreductase based on the copper ions-induced and NADH-mediated aggregation of gold-silver alloy nanoparticles

Hypoxia refers to the lack of oxygen supply to cells or tissues. The overexpression of nitroreductase has been shown to be closely related to the degree of hypoxia, which leads to the level of nitroreductase (NTR) being used as an indicator of hypoxia. We reported a facile visual detection of NTR based on the aggregation of gold and silver alloy nanoparticles. Compared with gold nanoparticles (AuNPs), the aggregation behavior of Au80Ag20 NPs caused a more prominent color change. Copper ions (Cu2+) can be rapidly reduced by nicotinamide adenine dinucleotide (NADH) under the catalysis of Au80Ag20 NPs. But NADH is consumed as an electron donor during the catalytic reduction reaction of p-nitrophenol (pNP) by NTR. A decrease of NADH amount results in the aggregation of Au80Ag20 NPs by the excess Cu2+ and different aggregation degrees of Au80Ag20 NPs lead to observable color change. A linear correlation of A600/A505 = 0.0285 [NTR]+0.361 (R2 = 0.980) was obtained with a limit of detection (LOD) of 0.23 μg/mL for UV–vis spectrophotometer. For visual detection, the values of R/B against the concentration of NTR obtains a calibration curve of R/B = −0.031 [NTR]+ 1.54 (R2 = 0.985) with a LOD of 0.76 μg/mL, which is of the same order of magnitude as the UV–vis spectrophotometer analysis. As a comparison, Au80Ag20 NPs was replaced by several different composition nanoparticles (Au NPs, Au70Ag30 NPs, Au50Ag50 NPs) to be a chromogenic substrate, and the results suggest the Au80Ag20 NPs is the most sensitive substrate in our assay. Selectivity tests showed that the detection system did not respond to other common substances, and the reaction mechanism was verified by inhibitor research. Finally, the assay was used on the human serum samples with spiking NTR, and the recovery rates of this assay with UV–vis spectrophotometer were basically consistent with RGB analysis.

Mechanism of Gold-Silver Alloy Nanoparticle Formation by Laser Coreduction of Gold and Silver Ions in Solution.

Photochemical reduction of aqueous Ag+ and [AuCl4]- into alloy Au-Ag nanoparticles (Au-Ag NPs) with intense laser pulses is a green synthesis approach that requires no toxic chemical reducing agents or stabilizers; however size control without capping agents still remains a challenge. Hydrated electrons produced in the laser plasma can reduce both [AuCl4]- and Ag+ to form NPs, but hydroxyl radicals (OH·) in the plasma inhibit Ag NP formation by promoting the back-oxidation of Ag0 into Ag+. In this work, femtosecond laser reduction is used to synthesize Au-Ag NPs with controlled compositions by adding the OH· scavenger isopropyl alcohol (IPA) to precursor solutions containing KAuCl4 and AgClO4. With sufficient IPA concentration, varying the precursor ratio enabled control over the Au-Ag NP composition and produced alloy NPs with average sizes less than 10 nm and homogeneous molar compositions of Au and Ag. By investigating the kinetics of Ag+ and [AuCl4]- coreduction, we find that the reduction of [AuCl4]- into Au-Ag NPs occurs before most of the Ag+ is incorporated, giving us insight into the mechanism of Au-Ag NP formation.

Synergistic catalytic activity of palladium–silver alloy nanoparticle for anodic oxidation of ethanol in alkali

Palladium and palladium-silver alloy nano catalysts were synthesized from aqueous precursor at room temperature via a single vessel chemical reduction and co-reduction methods in absence of capping agent. XPS analysis confirms the presence of Pd and Ag in the catalyst matrix. Microscopic analyses reveal spherical morphology of the catalyst in the nanoscale dimension. The electro-analytical investigation of the catalyst loaded on carbon electrode shows that the Pd4Ag nano alloy catalyst demonstrates marked improvement in electro-catalytic efficiency among all prepared catalysts for ethanol oxidation in alkali. The Pd4Ag/C catalyst shows the mass normalized peak current density of 522 mA mg−1Pd in cyclic voltammetric (CV) study, which is 1.97 times greater than that of similarly synthesized Pd/C (264.2 mA mg−1Pd) catalyst. Chronoamperometric and impedance analyses further establish the superiority of Pd4Ag/C catalyst. To discover the plausible mechanism, the CV study is typically extended to the intermediates like sodium acetate which reveals that though Pd is better for catalytic oxidation of intermediate than the best catalyst but the optimal OH− adsorption on the surface of the metal, favours catalytic oxidation of ethanol more on Pd4Ag catalyst. The mechanistic path of the reaction is anticipated by evaluating the ex-situ FTIR and chromatographic studies which explain the promotion of the formation of carboxylate in comparison to carbonate by Ag.

Antibacterial and Immunomodulatory Potentials of Biosynthesized Ag, Au, Ag-Au Bimetallic Alloy Nanoparticles Using the Asparagus racemosus Root Extract.

Two noble metals, such as silver and gold alloy nanoparticles, were successfully synthesized by the microwave assisted method in the presence of the Asparagus racemosus root extract and were used as an antibacterial and immunomodulatory agent. The nanostuctures of the synthesized nanoparticles were confirmed by various spectroscopic and microscopic techniques. The UV-vis spectrum exhibits a distinct absorption peak at 483 nm for the bimetallic alloy nanoparticles. The microscopic analysis revealed the spherical shaped morphology of the biosynthesized nanoparticles with a particle size of 10–50 nm. The antibacterial potential of the green synthesized single metal (AgNPs and AuNPs) and bimetallic alloy nanoparticles was tested against five bacterial strains. The bimetallic alloy nanoparticles displayed the highest zone of inhibition against P. aeurgnosia and S.aureus strains when compared to single metal nanoparticles and plant extract. In addition, the inmmunomodulatory potential of the root extract of A. racemosus, AgNPs, AuNPs, and Ag-Au alloy NPs is achieved by measuring the cytokine levels in macrophages (IL-1β, IL-6, and TNF-α) and NK cells (IFN-γ) of NK92 and THP1 cells using the solid phase sandwich ELISA technique. The results showed that the root extract of A. racemosus, AgNPs, and AuNPs can reduce the pro-inflammatory cytokine levels in the macrophages cells, while Ag-Au alloy NPs can reduce cytokine responses in NK92 cells. Overall, this study shows that the microwave assisted biogenic synthesized bimetallic nanoalloy nanoparticles could be further explored for the development of antibacterial and anti-inflammatory therapies.

Optical properties of polymer-graphene composites coated with gold and silver alloy nanoparticles

The plasmon resonance phenomenon occurring in the system of graphene-polymer-nanoparticles of an alloy of gold and silver is investigated. The possibility of controlling the attenuation of the intensity of electromagnetic radiation passing through the sample by changing the composition and thickness of the deposited coating is shown. For the investigated gold and silver alloy nanoparticles, the highest degree of radiation attenuation falls on the wavelength range from 400 to 600 nm. It was shown that by changing the composition of the nanoparticles (changing the ratio of gold and silver in the alloy), it is possible to achieve the maximum selective light attenuation by more than 2.5 times in the 500 nm region. In the 700 nm region, light attenuation by not more than 2 times is achieved. It was revealed that the use of films with different metal ratios allows us to shift the position of plasmon absorption in the entire visible wavelength range.

Nonlinear optical investigations of laser generated gold, silver and gold-silver alloy nanoparticles and optical limiting applications

Laser induced synthesis of gold, silver and gold-silver alloy nanoparticles in water and their nonlinear optical investigations are reported. The tunability of localized surface plasmon resonance band of the gold-silver alloy nanoparticles in the wavelength region between gold and silver was established using the UV–Visible absorption studies. The third order nonlinear optical properties like two photon absorption coefficient, optical limiting threshold, non linear refractive index and third order nonlinear optical susceptibility χ(3) of the nanoparticles could be fine tuned by controlling the volume ratios of gold and silver in the gold-silver alloy nanoparticles. The nonlinear optical behavior and optical limiting properties of the gold, silver and gold-silver alloy nanoparticles were found to be considerably affected by the position of inter and intra band absorption wavelength. Dual beam thermal lens method was utilized to determine the variations in photo thermal parameters like thermal diffusivity and thermal lens signal amplitude. The ability to tailor the nonlinear optical characteristics and photo thermal properties of the gold and silver nanoparticles employing the alloy nanoparticles makes them promising candidates in optical limiting, bio photonic, opto-electronic applications.

Preparation and electrochemical performances of silver (alloy) nanoparticles decorated on reduced graphene oxide, using self-polymerization of dopamine in an acidic environment

Self-polymerization of dopamine, in either an alkaline or an acidic environment, to form polydopamine is a material-independent surface coating technique, influencing almost all areas of material science and engineering. We demonstrated a simple, two-step method to prepare in-situ silver or silver-copper alloy nanoparticles on the surface of reduced graphene oxides, using polydopamine formed in an acidic medium. The acidic medium was created by a nonthermal micro-hollow cathode discharge device and the device was operated at atmospheric pressure, using air as the working gas. The nanocomposites were characterized with SEM, EDX, ICP-OES, and FT-IR; the electrochemical catalytic activity was tested using rotating disk electrode. The characterization methods confirmed the formation of the nanocomposites, which contain polydopamine, reduced graphene oxides, and metal nanoparticles or nanoalloy. We hypothesized that by alloying silver and copper on the surface of reduced graphene oxides, the oxygen reduction reaction (ORR) catalytic activity of the nanocomposites will be enhanced through both alloying and substrate effects. The size range of the nanoparticles is between 10 nm and 15 nm. We find that both the silver and alloy samples catalyze the ORR via a four-electron mechanism. The alloy nanocomposites showed better performance indicator parameters than the silver one, in both mass activity and kinetic current density. This preparation method has paved a new way of synthesizing an ORR catalyst in an environmentally friendly manner.

One-pot synthesis of monodisperse copper–silver alloy nanoparticles and their composition-dependent electrocatalytic activity for oxygen reduction reaction

Abstract Development of an economical, well-defined and efficient electrocatalyst having a potential to replace Pt/C is crucial for oxygen reduction reaction (ORR). In this respect, we report herein one-pot wet-chemical protocol for the composition-controlled synthesis of monodisperse CuAg alloy nanoparticles (NPs) and their composition-dependent electrocatalytic activities in ORR for the first time under an alkaline condition. The presented synthetic procedure yields CuAg NPs that exhibit monodisperse size distribution with an average particle diameter of ∼8 nm. Almost homogenous CuAg alloy formation is proved by using many advanced analytical techniques despite the considerable lattice mismatch between Cu and Ag. At all compositions investigated, the ORR activities of CuAg electrocatalysts are found to be significantly higher than monometallic Ag NPs. Improved ORR kinetics of CuAg alloy NPs are demonstrated by Tafel slopes (85 mV/dec for Cu30Ag70, 84 mV/dec for Cu40Ag60 and 78 mV/dec for Cu60Ag40 which are all smaller than that of monometallic Ag (113 mV/dec). Electrochemical impedance measurements support these findings and represent that charge transfer resistance strongly depends on composition of CuAg electrocatalyst. The ORR activity and surface analysis results put Cu40Ag60 forward since Cu oxidation is suppressed in Cu40Ag60 NPs, caused by Ag enhancement in the surface.

Atom transfer between precision nanoclusters and polydispersed nanoparticles: a facile route for monodisperse alloy nanoparticles and their superstructures.

Reactions between atomically precise noble metal nanoclusters (NCs) have been studied widely in the recent past, but such processes between NCs and plasmonic nanoparticles (NPs) have not been explored earlier. For the first time, we demonstrate spontaneous reactions between an atomically precise NC, Au25(PET)18 (PET = 2-phenylethanethiol), and polydispersed silver NPs with an average diameter of 4 nm and protected with PET, resulting in alloy NPs under ambient conditions. These reactions were specific to the nature of the protecting ligands as no reaction was observed between the Au25(SBB)18 NC (SBB = 4-(tert-butyl)benzyl mercaptan) and the very same silver NPs. The mechanism involves an interparticle exchange of the metal and ligand species where the metal-ligand interface plays a vital role in controlling the reaction. The reaction proceeds through transient Au25-xAgx(PET)n alloy cluster intermediates as observed in time-dependent electrospray ionization mass spectrometry (ESI MS). High-resolution transmission electron microscopy (HRTEM) analysis of the resulting dispersion showed the transformation of polydispersed silver NPs into highly monodisperse gold-silver alloy NPs which assembled to form 2-dimensional superlattices. Using NPs of other average sizes (3 and 8 nm), we demonstrated that size plays an important role in the reactivity as observed in ESI MS and HRTEM.

Alkyne/Ruthenium(II) Complex-Based Ratiometric Surface-Enhanced Raman Scattering Nanoprobe for In Vitro and Ex Vivo Tracking of Carbon Monoxide.

Here, we report a surface-enhanced Raman scattering (SERS) nanosensor for real-time ratiometric detection of carbon monoxide (CO) based on a ligand displacement mechanism. This nanoprobe consists of a gold-silver (Au-Ag) alloy nanoparticle core as the highly active SERS substrate, an alkyne/ruthenium(II) (alkyne/Ru(II)) complex immobilized on the surface as the CO-sensing element, and a porous silica shell to improve the stability and biocompatibility of the particle. Displacement of the alkyne ligand by CO results in a decrease of the alkyne vibrations and an increase of the metal carbonyl complex signals, thus allowing the effective ratiometric detection of CO in real-time. The great potential of this assay for CO detection is validated in clean buffer environments, live cells, and tissue slices.

Tailoring thermo-optical properties of eosin B dye using surfactant-free gold-silver alloy nanoparticles.

Surfactant free gold, silver and gold-silver alloy nanoparticles were synthesized using a laser mediated method for localized surface plasmon resonance tuning. The effect of these nanoparticles on the thermo-optical properties of eosin B dye was investigated. Dual beam mode matched thermal lens method was implemented to evaluate the thermal diffusivity of the eosin B with gold, silver and gold-silver alloy nanoparticles. Concentration and composition dependant changes in thermo-optical properties of the eosin B-nanoparticle systems were quantified. As the concentration of nanoparticles incorporated into the dye solution increased, the thermal diffusivity and fluorescence emission intensity of the samples were found to be decreased. At the same time an enhancement of the thermal lens signal was observed with the introduction of nanoparticles into the system. Further enhancement in signal and reduction in thermal diffusivity and fluorescence intensity can be obtained with fine tuning of surface plasmon resonance wavelength by gold, silver and gold-silver alloy nanoparticles.

Efficient single cell monitoring of pathogenic bacteria using bimetallic nanostructures embedded in gradient porous silicon

Plasmonics silver and palladium bimetallic alloy nanoparticles ((Ag@Pd)NPs) within gradient porosity silicon (GPSi) layer were prepared and investigated successfully as an efficient surface enhanced Raman scattering (SERS) active substrates. The GPSi was fabricated by dynamic etching process using CW, 405 nm, laser diode with a steady decrease of the etching current density from 80 mA/cm2 to 10 mA/cm2 with eight steps for an etching period of 2 min per step. Bimetallic alloy nanoparticles were prepared by ion reduction process. This was attained by immersing the GPSi in a salt solution containing AgNO3 and PdCl2; mixed at equal ratio for immersing time about 60, 120, 180, and 240 s. The bimetallic alloy SERS active substrates for bacterial detection as a function of immersion time were explored by using Field emission scanning electron microscopy, X-Ray diffraction and Fourier transform infrared spectroscopies and Raman measurements. Efficient SERS active substrates were achieved with a uniform and dense aggregation of nanoparticles on bacterial cells by controlling the immersion times. Aggregated bimetallic alloy nanoparticles into GPSi achieved a SERS enhancement factor (EF) 2.1 × 103, 8.6 × 104, 2.3 × 105, and 5.4 × 104 with 60, 120, 180, and 240 s immersion time, respectively for detecting an ultra-low concentration of about 1 Cfu/ml.

Electrochemical aptamer biosensor for As3+ based on apta deep trapped Ag-Au alloy nanoparticles-impregnated glassy carbon electrode

ABSTRACTArsenic is toxic, so being able to detect and monitor arsenic in aqueous environments is important. Here, we report a biosensor for As3+ (Arsenic (III)) which uses a glassy carbon electrode modified with Ag-Au alloy NPs (i.e. Silver and gold alloy nanoparticles) and loaded with an aptamer. The electrode contains apta deep trapped Ag-Au alloy NPs, and the detection method employs cyclic voltammetry and differential pulse voltammetry. Captured As3+ ions undergo electrochemical reaction, producing a significant increase in the current which is observed in the voltammetry curves. This current increase is a result of the electrocatalytic properties of the NPs. The electrode is used for the determination of As3+ in real water samples. The activity curve is linear for As3+ concentrations of 0.01µg/L to 10 µg/L, and the detection limit is 0.003 × 10−3µg/L. The operation of the biosensor is reproducible, stable, and selective, and the biosensor performs well in determining As3+ in water from natural water courses, lakes, and wells.

Enhancing luminescence in all-inorganic perovskite surface plasmon light-emitting diode by incorporating Au-Ag alloy nanoparticle

The localized surface plasmon enhanced luminescence behaviors of a radiating dipole in an all-inorganic perovskite light-emitting diode (PeLED) by incorporating a gold (Au)-silver (Ag) alloy nanoparticle (NP) in the electronic transport layer are demonstrated. The analyses of finite difference time domain (FDTD) show that the localized surface plasmon resonance (LSPR) wavelength mainly depends on the size and the material composition of NP. An increase of 25% of the luminescence efficiency can be achieved by selecting the proper size and the Au molar fraction of the alloy NP. This result can be attributed to the match between the LSPR wavelength of NP and emission peak of PeLED. And the luminous performance of PeLED can be improved by optimizing the thickness of functional layers. This finding indicates great potential of Au-Ag alloy nanoparticle in developing the efficiency of PeLEDs and provides a new method for the future improvement of PeLEDs.

Colorimetric detection of the β-agonist ractopamine in animal feed, tissue and urine samples using gold–silver alloy nanoparticles modified with sulfanilic acid

ABSTRACTA highly sensitive, selective and simple method was proposed for colorimetric detection of ractopamine on the basis of the interaction between ractopamine and sulfanilic acid-modified gold–silver alloy nanoparticles (AuAgNPs). The AuAgNPs were prepared by the reduction of HAuCl4 and AgNO3 with sodium citrate in aqueous medium and further modified by sulfanilic acid. The interaction of ractopamine with sulfanilic acid induced rapid aggregation of sulfanilic acid-modified AuAgNPs along with an optical colour change, leading to precise quantification which could be detected by absorptiometry. Under the optimum conditions, the absorbance ratio (A600/A435) of sulfanilic acid-modified AuAgNPs exhibited a linear relationship with the concentration of ractopamine in the range of 4.5–31.6 ng/mL. The detection limit of ractopamine was 1.5 ng/mL. The established novel colorimetric detection method showed high selectivity towards ractopamine. The method was successfully applied to detect ractopamine in spiked pork, swine feed and swine urine samples with excellent recoveries from 94.4% to 112.5%. These results demonstrated that the proposed new method has a good potential for practical applications.

Single step formation of biocompatible bimetallic alloy nanoparticles of gold and silver using isonicotinylhydrazide

Manufacturing nanoparticles with controlled physicochemical properties using environment-friendly routes have potential to open new prospects for a variety of applications. Accordingly, several approaches have been established for manufacturing metal nanoparticles. Many of these approaches entail the use of hazardous chemicals and could be toxic to the environment, and cannot be used readily for biomedical applications. In the present work, we report a single step bio-friendly approach to formulate gold (Au), silver (Ag), and Au-Ag alloy nanoparticles with desired surface corona and composition using isonicotinylhydrazide (INH) as a reducing agent. INH also functioned as a stabilizing agent by enabling a surface corona around the nanoparticles. Remarkably, within a single step INH could also provide a handle in regulating the composition of Au and Ag in bimetallic systems without any additional chemical modification. The physicochemical and surface properties of the different nanoparticles thus obtained have been examined by analytical, spectroscopic and microscopic techniques. Cell cytotoxicity (release of lactate dehydrogenase), cell viability and intracellular reactive oxygen species (ROS) assays confirmed that the Au, Ag, and Au-Ag bimetallic nanoparticles prepared with INH are biocompatible. Finally, the presence of organic surface corona of INH on the nanoparticles was found to impart nanozyme activity and antimycobacterial sensitivity to the nanoparticles.

Anticancer activity evaluation of green synthesised gold–silver alloy nanoparticles on colourectal HT‐29 and prostate DU‐145 carcinoma cell lines

Nanotechnology is an interesting way to produce and deal with fascinating features of materials. Metal nanoparticles offer a vast spectrum of potential applications in medicine and pharmaceutical sciences due to advances in nanotechnology research. This study was aimed to evaluate the anticancer properties of gold–silver (Au–Ag) alloy nanoparticles, which were synthesised using a green method by Galega officinalis ethanolic extract. The antitumour activity of biosynthesised nanoparticles has been assessed in vitro using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay on DU-145 and HT-29, prostate and colon cell lines, respectively. The Au–Ag alloy nanoparticles activity to inhibit the growth of cancer cell lines was recorded in terms of decrease in viable cell count in comparison with the control value. The spherical Au–Ag alloy nanoparticles with average size of 100 nm diameter were synthesised. The growth inhibition of the human prostate (DU-145) and colon carcinoma cell line (HT-29) has been found to be dose dependent. The calculated IC50 for the DU-145 cell line was 95.78 μg/ml after 24 h and for the HT-29 cell line was 70.66 µg/ml after 48 h. The results of this study suggest that Au–Ag alloy nanoparticles could be as an active substance against tumour cell lines and may be a beneficial treatment for cancer.