Au Bimetallic Nanoparticles Research Articles

Quantification of surface composition and segregation on AuAg bimetallic nanoparticles by MALDI MS.

In this work we show that it is possible to use MALDI-TOF as a tool to quantify the atomic composition and to describe the phase segragation of the surface of ligand-coated, bimetallic AuAg nanoparticles. Our investigation shows that AuAg nanoparticles of various compositions exhibit core-shell heterogeneity with surface enrichment of Ag. A Monte-Carlo type simulation demonstrates that the surface Au and Ag atoms arrange in a random fashion.

Surface functionalization of ZnO:Ag columnar thin films with AgAu and AgPt bimetallic alloy nanoparticles as an efficient pathway for highly sensitive gas discrimination and early hazard detection in batteries

This work presents the impact of surface decoration on the VOC sensing properties of ZnO:Ag columnar films by AgPt and AgAu bimetallic alloy nanoparticles.

Catalytic reduction of 4-nitrophenol using gold-silver alloy nanoparticles coated on alkali activated sand

Gold-Silver (Au-Ag) bimetallic alloy nanoparticles exhibit improved catalytic activity in comparison to the monometallic nanoparticles due to synergistic effect. In this work Au-Ag bimetallic alloy nanoparticles (BNPs) have been supported on alkali activated sand which acts as an inert support material, stabilizes the nanoparticles and prevents their agglomeration. In addition to providing high surface area for adsorption, sand is inexpensive and environmentally benign. Au-Ag alloy nanoparticles were prepared via co-reduction mechanism using polymer as a stabilising agent. Alkali activated sand was coated with the alloy nanoparticles using surface adsorption method. Efficient reduction of 4-Nitrophenol to 4-Aminophenol by NaBH4 in the presence of BNPs supported on alkali activated sand was investigated. Also, the heterogenous nature of the catalyst makes it highly reusable due to its effortless separation from the reaction medium.

Biosynthesis of Bimetallic Au-Ag Nanoparticles Using Escherichia coli and its Biomedical Applications.

Bimetallic nanoparticles act as a multifunctional platform because their properties are dependent on the composition, size, and shape, so their synthetic approaches and technological applications have fascinated many researchers. However, the rigorous reaction conditions and the hazardous chemicals are required during the chemical synthesizing processes. In this study, we develop a biosynthesis method of the bimetallic Au-Ag nanoparticles at room temperature without stabilizers or surfactants. In the solution containing Escherichia coli and Au ions, Au nanoparticles are first obtained upon increasing the pH. After Ag ions join, the core-shell Au-Ag nanoparticles are orderly produced. Transmission electron microscopy (TEM), UV-vis, Fourier transform infrared (FTIR) spectroscopy, energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction analysis (XRD), and X-ray photoelectron spectroscopy (XPS) are performed to confirm the structure and composition of biosynthetic Au-Ag nanoparticles. Furthermore, we have demonstrated that our bimetallic Au-Ag nanoparticles have greater application prospects in the ultrafast colorimetric detection of H2O2, photothermal therapy, and antibiotic therapy in comparison with single Au or Ag nanoparticles. Our bimetallic Au-Ag NPs could achieve the rapid and colorimetric detection of H2O2 without 3,3',5,5'-tetramethylbenzidine (TMB) and peroxidase. Moreover, Au-Ag NPs could enhance antibacterial ability but not increase their cytotoxicity, which provides a guarantee for the clinical applications of silver.

One-pot synthesis of Pd20-xAux nanoparticles embedded in nitrogen doped graphene as high-performance electrocatalyst toward methanol oxidation

Mixed Pd–Au bimetallic nanoparticles embedded nitrogen doped graphene composites (PdAu/NG180) are explored for efficient electrocatalytic oxidation of methanol. A simple hydrothermal one-pot polyol method, involving simultaneous reduction of both Pd and Au, is utilized for the synthesis of Pd20-xAux/NG180 (x wt % = 0, 5, 10 and 15). This method is of multiple advantages such as inexpensiveness, reagent-free and environment-friendly being surfactant free. The morphology, crystal structure and chemical composition of NG180, Pd/NG180 and Pd20-xAux/NG180 catalysts are analyzed by XRD, FESEM-EDX, TEM, XPS and Raman spectroscopy methods. Electrocatalytic activities of PdAu/NG180 nanocomposites toward methanol oxidation reaction (MOR) in alkaline media are investigated by cyclic voltammetry, chronoamperometry and CO stripping measurements. Pd20-xAux/NG180 exhibited an increase in the electroactive surface area of Pd to twice by the coexistence of Au. In cyclic voltammetry studies, Pd10Au10/NG180 catalyst exhibits highest peak current density for MOR and is 1.5 times highly efficient compared to Pd20/NG180 with an enhanced shift in the onset potential by 140 mV to lower overpotentials. Besides, Pd10Au10/NG180 catalyst exhibited enhanced electroactive surface area and long-time durability in comparison to Pd20/NG180 catalyst. The steady state current density for MOR observed with Pd10Au10/NG180 at the end of 4000 s (98 mA mg−1Pd) is higher than those observed with all the other catalysts at the end of mere 1000 s alone (97, 61, and 32 mA mg−1Pd). The promising high electrocatalytic activity of Pd10Au10/NG180 is well corroborated from CO stripping experiments that the specific adsorption of CO onto Pd10Au10/NG180 (0.71 C m−2) is merely half to that observed onto Pd20/NG180 (1.49 C m−2).

A one-pot synthesis of colloidal Ag–Au nanoparticles with controlled composition

We report a one-pot synthesis method for a production of a stable Ag–Au bimetal colloidal solutions (Ag–Au hydrosols) by simply mixing disodium salt of ethylenediaminetetraacetic acid (Na2EDTA) with AgNO3 and HAuCl4 in aqueous alkaline medium at 80 °C. We found that Na2EDTA act not only as a reductant of metal ions and a potent stabilizer of metal nanoparticle size, but also as an effective agent for controlling the composition of the formed nanoparticles, owing to the high complexing affinity of Na2EDTA to silver ions. It was found that by controlling Na2EDTA concentration in the reaction mixture it is possible to control not only size and size distribution of a synthesized colloidal bimetallic Ag–Au nanoparticles, but bimetallic Ag–Au nanoparticles composition (Ag/Au ratio) as well.

Bio-inspired synthesis and cytotoxic evaluation of silver-gold bimetallic nanoparticles using Kei-Apple (Dovyalis caffra) fruits

This work presents the synthesis and cytotoxic properties of monometallic nanoparticles (NPs) of Ag, Au and their AuAg bimetallic nanoparticles (BNPs) using Kei apple fruit extract. The BNPs were prepared by varying the concentrations of the plant extract and the precursor salts (AgNO3 and HAuCl4). UV–visible spectroscopic methods showed surface plasmon resonance around 430 and 532 nm for the Ag and Au NPs respectively. The plasmon bands of the BNPs were recorded around 540 nm. Powder X-ray diffraction (pXRD) analysis and transmission electron microscopic (TEM) studies showed the crystalline nature and monodispersity associated with the monometallic nanoparticles. However, a clear evidence of polydispersity was apparent in the case of the bimetallic nanoparticles. The anticancer assay of the synthesized nanoparticles showed promising activities with the BNPs exhibiting higher potential with respect to the reaction conditions. The BNPs synthesized using higher volume of the fruit extract (AuAg BNPs3) gave the best anticancer properties against breast cancer MCF7 cell line whereas the AuNPs gave an IC50 of 105 μM as the least potent nanoparticles.

The Synthesis of SiO2@AuAg@CeO2 Sandwich Structures with Enhanced Catalytic Performance Towards CO Oxidation

AbstractNovel sandwich structure SiO2@AuAg@CeO2 nanospheres (SACs), as low‐temperature CO oxidation catalysts, were designed and prepared in this work. The SACs include SiO2 nanosphere support, embedded bimetallic AuAg nanoparticles, and CeO2 shell. The transmission electron microscope (TEM), elemental mapping images, and ultraviolet‐visible (UV‐vis) spectroscopy indicated the successful fabrication of the SACs sandwich structure. The catalytic performance of SACs varies with the AuAg composition and achieves the best catalytic activity when Au/Ag atomic ratio is 2:1. The strong synergistic effect of AuAg alloy remarkably promotes the CO oxidation through facilitating the adsorption of CO and O2 on the AuAg nanoparticles. The CeO2 non‐compact shell not only provides effective protection for AuAg nanoparticles from aggregation but also gives CO full access to the catalysts. With unique sandwich structure and specific chemical composition, the SiO2@Au2Ag1@CeO2 nanospheres with CeO2 shell thickness of 5 nm present excellent low‐temperature catalytic activity and high‐temperature thermal stability.

Enhancement of Single Molecule Raman Scattering using Sprouted Potato Shaped Bimetallic Nanoparticles

Herein, for the first time, we report the single molecule surface enhanced resonance Raman scattering (SERRS) and surface enhanced Raman scattering (SERS) spectra with high signal to noise ratio (S/N) using plasmon-active substrates fabricated by sprouted potato shaped Au-Ag bimetallic nanoparticles, prepared using a new one-step synthesis method. This particular shape of the nanoparticles has been obtained by fixing the amount of Au and carefully adjusting the amount of Ag. These nanoparticles have been characterized using scanning electron microscopy, extinction spectroscopy, and glancing angle X-ray diffraction. The single molecule sensitivity of SERS substrates has been tested with two different molecular Raman probes. The origin of the electromagnetic enhancement of single molecule Raman scattering in the presence of sprouted shape nanoparticles has been explained using quasi-static theory as well as finite element method (FEM) simulations. Moreover, the role of (i) methods for binding Raman probe molecules to the substrate, (ii) concentration of molecules, and (iii) Au-Ag ratio on the spectra of molecules has been studied in detail.

Gas Sensing with Nanoplasmonic Thin Films Composed of Nanoparticles (Au, Ag) Dispersed in a CuO Matrix

Magnetron sputtered nanocomposite thin films composed of monometallic Au and Ag, and bimetallic Au-Ag nanoparticles, dispersed in a CuO matrix, were prepared, characterized, and tested, which aimed to find suitable nano-plasmonic platforms capable of detecting the presence of gas molecules. The Localized Surface Plasmon Resonance phenomenon, LSPR, induced by the morphological changes of the nanoparticles (size, shape, and distribution), and promoted by the thermal annealing of the films, was used to tailor the sensitivity to the gas molecules. Results showed that the monometallic films, Au:CuO and Ag:CuO, present LSPR bands at ~719 and ~393 nm, respectively, while the bimetallic Au-Ag:CuO film has two LSPR bands, which suggests the presence of two noble metal phases. Through transmittance-LSPR measurements, the bimetallic films revealed to have the highest sensitivity to the refractive index changes, as well as high signal-to-noise ratios, respond consistently to the presence of a test gas.

3D graphene/MWNTs nano-frameworks embedded Ag-Au bimetallic NPs for carcinoembryonic antigen detection

In this work, a novel electrochemical immunosensor was designed for ultrasensitive determination of carcinoembryonic antigen based on 3D-structured rGO/Ag-Au NPs. 3D-rGO-MWCNTs nanocomposites feature network structure which has a large specific surface area and excellent conductivity providing more active sites for Ag-Au bimetallic nanoparticles. At the same time, the synergistic effect of 3D-rGO-MWCNTs and Ag-Au NPs, significantly improved the electrochemical performance of the modified electrode. Due to the excellent biocompatibility of Ag-Au NPs, the antibody could be well attached to the electrode, and the immunosensor could be successfully prepared. Under the optimized conditions, the constructed immunosensor showed a wide linear range from 0.001 ng mL−1 to 80 ng mL−1 with the detection limit of 3 pg mL−1 (S/N ratio of 3). The proposed immunosensor has excellent analytical performance including good stability, reproducibility and selectivity, and was successfully applied to the detection of CEA in human serum verified its practicability.

Enhanced Morphological Properties of Macroporous Silicon with the Incorporation of Au-Ag Bimetallic Nanoparticles for Improved CO2 Gas Sensing

In this work, the effects of incorporating bare macroporous silicon (macro-Psi) layer with bimetallic nanoparticles Au-Ag on the performance Psi CO2 gas sensor synthesized by a laser-assisted etching (LAE) process were investigated. Well-controlled and simple immersion process of bare macro-Psi layer in the 10−3 M of silver nitrate (AgNO3) and chloroauric acid (HAuCl4) individually and in the mixing solution with ratio 1:1 was employed to synthesize monometallic AuNPs/macro-Psi, AgNPs/macro-Psi, and bimetallic Au-AgNPs/macro-Psi hybrid structures of CO2 gas sensors. Morphological properties of bare macro-Psi layer, monometallic, and bimetallic hybrid structures were investigated using X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), and energy-dispersive X-ray analysis (EDS). Electrical characteristics (I–V)of the sensor were measured primary in a vacuum case and with CO2 at 0.2, 0.5, 1, and 1.5 mbar gas pressures. The result showed a significant enhancement in sensitivity and temporal response of the bimetallic hybrid structures compared with that of monometallic and bare macro-Psi layer and an enhanced performance of the sensors due to the high value of integrated specific surface area of the bimetallic nanoparticles and the resulting Schottky barrier height.

Green synthesis of reduced graphene oxide-AgAu bimetallic nanocomposite: Catalytic performance

In this study, we prepared lichen reduced-graphene oxide (LrGO)-bimetallic nanoparticle nanocomposites (LrGO-AgAu) by applying a green, facile and one pot approach. LrGO-AgAu was synthesized via simultaneous reduction of graphene oxide (GO), AgNO3 and HAuCl4 with Cetraria Islandica (L.) Ach. extract. Characterization of the prepared nanocomposites were carried out by transmission electron microscopy (TEM), scanning electron microscopy (SEM), ultraviolet-visible (UV-Vis) spectroscopy, X-Ray Diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). The synthesized LrGO-AgAu bimetallic nanoparticle nanocomposites were used for catalytic conversion of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) with NaBH4. The effect of nanocomposite composition on catalytic activity was examined. It is obtained that AgAu bimetallic nanoparticles with small particle sizes were decorated LrGO nanosheets homogenously and superior catalytic performance was achieved for the decomposition of 4-NP. The results showed that catalytic reduction reaction of 4-NP to 4-AP with noble metallic NPs nanocatalysts obtained by lichen extract is a facile and low-cost approach for removal.

Formation and Stabilization of Au, Ag, Ru, and Rh Metallic and Bimetallic Nanoparticles in Inverse Micellar Solutions

The work presents research data on the optical properties of nanosized particles of silver, gold, rhodium and ruthenium prepared by chemical reduction of the Men+ ions in inverse micellar solutions (IMS) in the presence of molecular oxygen and the flavonoid reducer quercetin. Metallic nanoparticles and the bimetallic particles Au/Ag, Au/Ru, and Au/Rh were produced by the molecule-by-molecule method. Using UV–VIS spectrophotometry, the spectral characteristics of the monometallic and bimetallic nanoparticles were examined, and the kinetics of their formation in IMS was studied.

Synthesis of nitrogen-doped reduced graphene oxide loading with Au-Ag bimetallic nanoparticles for electrochemical detection of daunorubicin

Nitrogen-doped reduced graphene oxide loading with Au-Ag bimetallic nanoparticles (NG-Au-Ag) was synthesized by a facile two-step strategy. The successful formation of NG-Au-Ag nanocomposites were confirmed by transmission electron microscopy (TEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis. Furthermore, NG-Au-Ag nanocomposites were modified onto the electrode surface for the voltammetric detection of daunorubicin (DNR). The results showed that the NG-Au-Ag modified electrode expressed high electrocatalytic activity toward the redox of DNR, allowed detection of DNR with wide linear range (0.01 μg mL−1 to 15 μg mL−1) and low detection limit (3 ng mL−1). The modified electrode also exhibited satisfactory performance for the detection of DNR in human serum samples.

Nanocomposite thin films based on Au-Ag nanoparticles embedded in a CuO matrix for localized surface plasmon resonance sensing

Nanocomposite thin films, composed of monometallic Au and Ag, and bimetallic AuAg nanoparticles, dispersed in a CuO matrix were prepared, characterised and tested for Localized Surface Plasmon Resonance (LSPR) sensing. The films were deposited by reactive magnetron sputtering, followed by a post-deposition thermal annealing to modify the size and shape of the nanoparticles distribution within the oxide matrix. Regarding the main results of the monometallic systems, the Au:CuO films showed LSPR bands from 800 nm to 650 nm, which reveal a progressive narrowing and a continuous blue-shift with increasing temperature (400–700 °C). The Ag:CuO films evidenced plasmonic bands at about 400 nm for temperatures of 500 °C and above. The bimetallic system, Au-Ag:CuO, showed LSPR bands in the range between those of the corresponding monometallic systems, due to the presence of Ag enriched AuAg alloy nanoparticles, taking part of Janus-like structures in some cases. In terms of LSPR sensing, Au:CuO films revealed the highest values of refractive index sensitivity since the nanoparticles are more exposed to the surrounding environment.

Cytotoxicity of Ag, Au and Ag-Au bimetallic nanoparticles prepared using golden rod (Solidago canadensis) plant extract

Production and use of metallic nanoparticles have increased dramatically over the past few years and design of nanomaterials has been developed to minimize their toxic potencies. Traditional chemical methods of production are potentially harmful to the environment and greener methods for synthesis are being developed in order to address this. Thus far phytosynthesis have been found to yield nanomaterials of lesser toxicities, compared to materials synthesized by use of chemical methods. In this study nanoparticles were synthesized from an extract of leaves of golden rod (Solidago canadensis). Silver (Ag), gold (Au) and Ag-Au bimetallic nanoparticles (BNPs), synthesized by use of this “green” method, were evaluated for cytotoxic potency. Cytotoxicity of nanomaterials to H4IIE-luc (rat hepatoma) cells and HuTu-80 (human intestinal) cells were determined by use of the xCELLigence real time cell analyzer. Greatest concentrations (50 µg/mL) of Ag and Ag-Au bimetallic were toxic to both H4IIE-luc and HuTu-80 cells but Au nanoparticles were not toxic. BNPs exhibited the greatest toxic potency to these two types of cells and since AuNPs caused no toxicity; the Au functional portion of the bimetallic material could be assisting in uptake of particles across the cell membrane thereby increasing the toxicity.

Green synthesis of Ag, Au and Ag-Au bimetallic nanoparticles using Stigmaphyllon ovatum leaf extract and their in vitro anticancer potential

Noble metals nanoparticles have shown interesting prospects towards biomedical applications, and their bimetallic counterparts are envisaged to be more promising. In this study, the Stigmaphyllon ovatum leaf extract was used for the synthesis of silver, gold and silver-gold bimetallic nanoparticles (AgNPs, AuNPs and Ag-Au BNPs) in an aqueous medium. Surface plasmon bands were obtained at 420, 550 and 542 nm for the AgNPs, AuNPs and Ag-Au BNPs respectively. Only one absorption band was observed in the spectra of the bimetallic nanoparticles, which suggested the formation of a nanoalloy. Particle sizes of about 24, 80 and 15 nm were obtained for the AgNPs, AuNPs and Ag-Au BNPs respectively. The effect of the nanoparticles on Human cervical carcinoma (HeLa) cells revealed cytotoxic effects towards the growth of the carcinoma cells with the IC50 values of 5.75 × 10−16, 9.1 × 10−9 and 0.0027 µM for the Ag-Au BNPs, AgNPs and AuNPs, respectively. The nanoparticles were excellently efficient compared to the standard drug, 5-fluorouracil with an IC50 value of 40 µM. These nanoparticles however opened up new perspectives in research and may provide promising alternative approaches for nano-drug development in the next generation of effective anticancer drugs.

Development of visible-light-responsive morphology-controlled brookite TiO2 nanorods by site-selective loading of AuAg bimetallic nanoparticles

Morphology-controlled brookite TiO2 nanorods loaded with AuAg bimetallic nanoparticles were synthesized by a facile photoreduction process to develop visible-light-responsive photocatalytic performance. The AuAg bimetallic nanoparticles provide good stability and excellent localized surface plasmon resonance (LSPR) effect. Moreover, the AuAg bimetallic nanoparticles were selectively deposited on the reduction facets of brookite TiO2 nanorods, facilitating the charge separation. As expected, the as-prepared AuAg-TiO2 nanorods showed enhanced visible light harvesting and decreased electron-hole recombination, resulting in superior visible-light-responsive photocatalytic performance. When the loading amount of AuAg nanoparticles was controlled at 0.5 wt%, the AuAg-TiO2 nanorods yield 102 ppm acetone with visible-light irradiation for 5 h, far exceeding than those of bare brookite TiO2 nanorods.

Green synthesis and electrochemistry of Ag, Au, and Ag–Au bimetallic nanoparticles using golden rod (Solidago canadensis) leaf extract

Silver (Ag) nanoparticles (NPs), gold (Au) NPs, and silver–gold (Ag–Au) bimetallic nanoparticles (BNPs) were synthesized by use of golden rod leaf extracts. Aqueous solutions of the precursor compounds HAuCl4·xH2O and AgNO3 were mixed individually and jointly with aqueous extract of golden rod leaf and heated with stirring at 80 °C for 1 h. There were observed periodic changes in color which indicate the formation of nanoparticles, and were confirmed by use of UV–Vis spectroscopy. Sizes of NPs were determined by X-ray diffraction and transmission electron microscopy while bioreductants were examined using Fourier transform infrared spectroscopy. In BNPs, both Au and Ag were detected in an unequal ratio. This observation shows that the gold ions were more prone to reduction by the plant biomolecules than the silver ions which may be a unique character due to Solidago canadensis leaf extract and different reduction potentials of the metals. Formation of Ag, Au, and Ag–Au BNPs were suggested by appearance of bands at 420, 560, and 530 nm, respectively. Sizes and shapes of Ag–Au BNPs resemble pure Au NPs more than they do Ag NPs. Electrochemical characterization of NPs by use of cyclic voltammetry showed that Ag–Au BNPs were more electroactive compared to other electrodes. This work therefore accentuates the effect of substrate and precursor concentrations towards nanoparticle formation which could enhance material application depending on the reaction techniques.