Au Bimetallic Nanoparticles Research Articles

Novel biochar supported heterojunction of RH-BC (Fe0/Au0) catalyst: A highly efficient catalyst in the degradation of micro-pollutants

The loading of Fe and Au bimetallic nanoparticles onto the bio-char (RH-BC, rice husk derived) using the novel and eco-friendly process yielded heterojunction RH-BC (Fe0/Au0) nanocomposite. The Artocarpus heterophyllus Lam phytochemicals enable the in situ synthesis of these nanoparticles. Various analytical tools characterize the materials to a greater extent. The photo-Fenton-like processes under dark, LED-VIS, and UV-A light irradiations assess the efficiency of heterojunction catalyst in the degradation of potential micro-pollutants viz., tetracycline hydrochloride and N-(n-propyl) thiourea. Indigenous batch reactor operations optimize the parametric studies, viz., pH of the solution, catalyst dosage, and hydrogen peroxide dosage in the removal process. The maximum degradation of targeted pollutants in the photo-Fenton-like process was 93.75% (LED-VIS), 98.43% (UV-A) for TC, while 92.48% (LED-VIS), 93.57% (UV-A) for N-(n-propyl) thiourea, respectively. The parametric studies demonstrate the mechanistic aspects of the degradation process. The repeated use of the catalyst for five consecutive cycles showed an equivalent rate of degradation percentage and hence showed fair stability. The successful application of the novel Fenton-like catalyst in a real water system showed an insignificant change in percentage degradation, which raises the possibility of a broader application to the treatment of water contaminated by these potential micropollutants.

Silver-Gold Alloy Nanoparticles (AgAu NPs): Photochemical Synthesis of Novel Biocompatible, Bimetallic Alloy Nanoparticles and Study of Their In Vitro Peroxidase Nanozyme Activity.

Facile synthesis of metal nanoparticles with controlled physicochemical properties using environment-friendly reagents can open new avenues in biomedical applications. Nanomaterials with controlled physicochemical properties have opened new prospects for a variety of applications. In the present study, we report a single-step photochemical synthesis of ~5 nm-sized silver (Ag) and gold (Au) nanoparticles (NPs), and Ag-Au alloy nanoparticles using L-tyrosine. The physicochemical and surface properties of both monometallic and bimetallic NPs were investigated by analytical, spectroscopic, and microscopic techniques. Our results also displayed an interaction between L-tyrosine and surface atoms that leads to the formation of AgAu NPs by preventing the growth and aggregation of the NPs. This method efficiently produced monodispersed NPs, with a narrow-sized distribution and good stability in an aqueous solution. The cytotoxicity assessment performed on breast cancer cell lines (MCF-7) revealed that the biofriendly L-tyrosine-capped AgNPs, AuNPs, and bimetallic AgAu NPs were biocompatible. Interestingly, AgAu NPs have also unveiled controlled cytotoxicity, cell viability, and in vitro peroxidase nanozyme activity reliant on metal composition and surface coating.

IN VITRO ANTICANCER POTENTIAL OF PHYTOGENIC AG-AU BIMETALLIC NANOPARTICLES USING CLITORIA TERNATEA FLOWER EXTRACT

Bimetallic nanoparticles (BNPs) have gained significant attention in the field of biomedical and pharmaceutical because of its tunable size, shape, high surface to volume and enhanced biological properties. In this study, we report the ecofriendly route to produce the noble (Ag-Au) bimetallic nanoparticles using aqueous flower extract of Clitoria ternatea as a reducing and capping agent. The synthesized C.T-Ag-Au BNPs were characterized by using physicochemical techniques such as UV-visible, FTIR, XRD and SEM-EDX analysis. The UV-visible spectra reveal the formation of homogeneous bimetallic nanoparticles by the single blue-shifted peak at 541 nm of C.T-Ag-Au BNPs. The phyto fabrication of synthesized C.T-Ag-Au BNPs was analyzed using FTIR spectroscopy. XRD confirms the formation of phase pure cubic Ag-Au alloy bimetallic nanoparticles with crystallite size is 14.5 nm. The surface morphology and elemental analysis of C.T-Ag-Au BNPs were examined by using SEM-EDX analysis. The synthesized C.TAg- Au BNPs were evaluated for their cytotoxicity against A549 human lung cancer cells through standard MTT assay. From this assay, green synthesized bimetallic nanoparticles induced cell apoptosis, suggesting that the synthesized C.T-Ag-Au BNPs gave best anticancer properties against lung cancer A549 cell lines.

SERS of thiabendazole on silver-gold bimetallic nanoparticles: Adsorption mechanism

Au-Ag bimetallic nanoparticles (BNPs) with varying molar fractions as Au0.2Ag0.8 and Au0.3Ag0.7 are prepared on porous silicon. They were demonstrated as surface-enhanced Raman scattering (SERS) substrate for the detection of thiabendazole (TBZ) molecules. The concentration of TBZ investigated is 10-7 M. The effect of the Au content on SERS properties of the Au-Ag BNPs was studied. Furthermore, the composition dependent SERS spectra and adsorption mechanism of TBZ on Au-Ag BNPs surfaces were discussed.

Synthesis of Au-Ag bimetallic nanoparticles using Korean red ginseng (Panax ginseng Meyer) root extract for chemo-photothermal anticancer therapy.

Green synthesis strategies have been widely applied for the preparation of versatile nanomaterials. Gold nanospheres with an average size of 6.95 ± 2.25nm were green synthesized by using a 70% ethanol extract of Korean red ginseng (Panax ginseng Meyer) root as a reducing agent. A seed-mediated synthesis was conducted to prepare Au-Agbimetallic nanoparticles using gold nanospheres as seeds. Remarkably, Au-Ag bimetallic nanoparticles with an average size of 80.4 ± 11.9nm were synthesized. Scanning transmission electron microscopy, energy dispersive X-ray spectroscopy and elemental mappings revealed bimetallic nanoparticles with Au-Ag alloy core and Au-rich shells. A face-centered cubic structure of Au-Ag bimetallic nanoparticles was confirmed by X-ray diffraction analysis. For Au-Ag bimetallic nanoparticles, the ratio of Ag/Au was 0.20 which was detected and analyzed by inductively coupled plasma-mass spectrometry. Gold nanospheres and Au-Ag bimetallic nanoparticles were functionalized by PEGylation, folic acid conjugation and grafting onto graphene oxide. Finally, docetaxel was loaded for evaluating the in vitro cell viability on cancer cells. Successful functionalization was confirmed by Fourier-transform infrared spectra. The anticancer activity of the docetaxel-loaded nanoparticles was higher than that of their non-docetaxel-loaded counterparts. The highest anticancer activity on human gastric adenocarcinoma cells (AGS) was observed in the docetaxel-loaded gold nanospheres that were functionalized by PEGylation, folic acid conjugation and grafting onto graphene oxide. Additionally, grafting onto graphene oxide and docetaxel loading induced high intracellular reactive oxygen species generation. For chemo-photothermal (PTT) anticancer therapy, cell viability was investigated using near-infrared laser irradiation at 808nm. The highest chemo-PTT anticancer activity on AGS cells was observed in the docetaxel-loaded Au-Ag bimetallic nanoparticles. Therefore, the newly prepared docetaxel-loaded Au-Ag bimetallic nanoparticles in the current report have potential applications in chemo-PTT anticancer therapy.

Electrochemical and electrocatalytic performance of single Au@Pt/Au bimetallic nanoparticles

Bimetallic nanoparticles (NPs) are widely used in energy catalysis, chemical synthesis, and chemical/biosensing, but their performance at single NPs level is still needed to investigate. In this work, bimetallic Au@Pt/Au NPs with triple-layered core-shell structure was successfully prepared and characterized. The single bimetallic Au@Pt/Au NPs were immobilized on the surface of Au nanoelectrode through electrostatic adsorption. The results have showed that the single Au@Pt/Au NPs have size-dependent properties for voltametric response and electron-transfer rate, and exhibit excellent electrocatalytic activity, long-term tolerance and anti-toxicity compared with the traditional Pt catalyst. This work provides new insight into conventional electrocatalysis and will likely give a good platform for designing entirely new catalysts at single NPs level.

Impedimetric nano-collision Escherichia coli analysis based on Silver-Gold bimetallic nanoparticles

An impedimetric detection of E. coli was developed using chemically synthesised bimetallic Ag-Au (1:2) nanoparticles (NPs). The UV–visible spectra of the NPs had absorption bands at 470 and 580 nm for Ag NPs and Au NPs, respectively. In the presence of E. coli, a negative potential shift and a blue shift was observed in the voltammograms and spectra respectively. The complex formed had an oxidation potential at + 0.95 V. Technique choice was based on sensitivity comparison of Differential pulse voltammetry, cyclic voltammetry and impedance spectroscopy in 0.1 M PBS with Impedance being the best choice. Optimum sensing conditions of the NPs-E. coli complex for NPs concentration, incubation period, method modulation amplitude and applied potential were 5 mM, 20 min, 10 mV and + 0.5 V, respectively. The sensor’s linearity range, lower limits of detection and quantification were found to be 101-107, 1.88 × 101, 2.34 × 102 cells/mL, respectively. The sensor’s applicability was validated by repeatability, stability and selectivity studies showing minimum changes in signal. Potential usage of the sensor in real samples was demonstrated by standard addition analysis of sea and River water samples as well as recovery of spiked water and fruit juices with acceptable % RSD < 2%.

Influence of Cluster Sources on the Growth Mechanisms and Chemical Composition of Bimetallic Nanoparticles

Metal nanoparticles are omnipresent in today’s applied and fundamental research. Both wet-chemical as well as physical procedures for their fabrication are well-established, where the latter is of particular interest as they supply surfactant-free particles. Particle growth has been investigated for several decades, but due to its complexity, involving kinetic and dynamic processes on various length and time scales, often only phenomenological rules of thumb are available. In this study, we report on bimetallic AgAu nanoparticles and demonstrate how the additional degree of freedom of the chemical composition can be used to derive information about how and where the particles grow, depending on two different cluster source types (hollow magnetron vs laser vaporization). The chemical composition is quantified on the single-particle level using electron-induced X-ray spectroscopy (STEM-EDS) and shows significant differences for the two fabrication routes. Based on molecular dynamics and Monte Carlo simulations, we derive that for hollow cylindrical sources both the mean particle size and the chemical composition are determined within the plasma region, where particles not only grow but also evaporate low-boiling silver. The comparably large plasma plays a decisive role here, as opposed to planar magnetron or laser vaporization sources, where no such evaporation is observed. These results shed light into the complex cluster growth and help understanding and optimizing nanoscale fabrication processes.

Molecularly imprinted 3D SERS sensor with inorganic frameworks for specific and recyclable SERS sensing application.

Poor selectivity and reusability of Au/Ag nanostructures are the main challenges for surface-enhanced Raman spectroscopy (SERS) in real sample detection. Herein, a novel specific and reusable three-dimensional (3D) SERS sensor with dual functions of selective trapping and photocatalytic degradation was designed. Firstly, Au-Ag bimetallic nanoparticles decorated silicon nanowires array (SiNWs-AuAg) wereprepared as 3D SERS substrate. Then,silicon-based inorganic-framework molecularly imprinted TiO2 (TiO2@SiMIP) was synthesized and immobilized on SiNWs-AuAg by using rhodamine 6G (R6G) as template molecule. Owing to the excellent SERS performance of SiNWs-AuAg and the specific affinity of TiO2@SiMIP to template molecule, the prepared SERS sensor enables sensitive and selective detection of R6G in food samples with a limit of detection (LOD) of 0.27 nM. In addition, due to the photocatalysis of TiO2 and the stability of silicon-based inorganic framework, the residual templates in TiO2@SiMIP can be completely removed by UV irradiation, and the imprinted cavity of regenerated sensors still maintained good selectivity after regeneration by UV irradiation.

Influence of swift heavy ion irradiation on bimetallic gold-silver nanoparticles in dielectric matrices and their optical properties

Nanosized gold-silver (AuAg) alloy nanoparticles (NPs) of sizes, 2 nm -25 nm embedded in fused quartz are synthesized using sequential implantation and post annealing at 900℃ for 1 h in Argon environment. The post annealed film is irradiated using swift heavy ions (SHI), 120 MeV Ag ions to investigate the effect of electronic energy deposition, (Se×ϕ), on size, shape and composition of the alloy NPs. Transmission electron microscopy (TEM) analysis of the as- implanted AuAg film reveals the formation of small sized, 1.8 nm-3.5 nm, bimetallic AuAg NPs. Rutherford backscattering spectroscopy (RBS) spectra along with its fitted graph convey the annealing induced out diffusion, mixing and formation of larger sized, 2 nm -25 nm, alloy NPs through Ostwald ripening. SHI irradiation results in deformation in shape from spherical to ellipsoidal alloy NPs with major axis align along the beam direction and the average aspect ratio is about 1.20. RBS analysis results convey the formation of Ag enriched alloy NPs after irradiation. The smaller nanoparticles are found dissolved while larger ones grow and elongate along the ion beam direction. SPR properties are modified by SHI induced processes of melting, sputtering and re-precipitation in the ion tracks.The un-irradiated film exhibits a single intense SPR peak at 536 nm, while the irradiated film gives rise two SPR peaks: Ist, a blue shifted SPR peak from 536 nm to 515 nm with significantly reduced intensity and much wider FWHM; and, IInd, a small SPR peak around 460 nm. SHI induced modifications on the NPs are understood in terms of thermal spike model. The detailed analysis shows that SHI can be used as a tool to tailor size, shape and composition of the bimetallic AuAg alloy NPs and their SPR properties.

Synthesis of bimetallic Ag-Au nanoparticles for surface-enhanced Raman scattering spectroscopy

In this report, bimetallic Au-Ag nanoparticles were successfully prepared by a chemical strategy using binary reduction agents. The metal ratio in bimetallic nanoparticles can be easily tuned by controlling the metal precursor ratio. Using Rhodamine as a probe molecule, we investigated the surface-enhanced Raman scattering (SERS) activity of synthesized bimetallic Au-Ag nanoparticles. The results demonstrate that our materials allow to enhance about 2×106 times the Raman signal of Rhodamine. Hence, the combination of unique features of two plasmonic metals opens up exciting prospects for the design of an ultra-sensitive sensor based on SERS.

Effective visible-light-driven photocatalytic degradation of fenitrothion by s-gC3N4/Ag-Au bimetallic nanocomposite

ABSTRACT This paper reports on the optimization of fenitrothion photocatalytic degradation in visible light based on Plackett Burman (PB) design and central composite design (CCD) in response surface methodology (RSM). A herbicide routinely used with a negative impact on the environment is fenitrothion, which must be degraded to minimize the impact on the environment. For fenitrothion degradation, Ag-Au bimetallic nanoparticles on the semiconducting s-doped gC3N4 surface were synthesized using the galvanic exchange. The properties of s-gC3N4/Ag-Au bimetallic nanocomposite were confirmed by various methods. Significant factors responsible for fenitrothion photocatalytic degradation were determined using Plackett-Burman (PB) design and were catalyst dosage, initial fenitrothion concentration, H2O2 concentration, pH, and rotational speed. Central composite design (CCD) design was used for further optimization. The optimum conditions for the maximum degradation of fenitrothion (100%) constraints were found to be 100% an amount of H2O2 concentration 60 mM, pH 10, rotational speed 700 rpm. These results showed that s-gC3N4/Ag-Au bimetallic nanocomposite could act as a suitable photocatalyst under visible light in the degradation of fenitrothion. By removing fenitrothion from real water samples, as well as by maintaining its stability and reusability in five successive cycles, the practicality of this nanocomposite was demonstrated.

A Facile Preparation of Reduced Graphene Oxide Capped AuAg Bimetallic Nanoparticles: A Selective Nanozyme for Glutathione Detection

AbstractOver the last decade, artificial enzymes (nanozymes) have undergone substantial development in the field of sensing. In this study, Au−Ag bimetallic nanoparticles (NPs) decorated on reduced graphene oxide sheets (AuAg‐rGO) nanocomposite has been developed as a novel colorimetric probe based on the peroxidase imitating activity of the nanozyme. AuAg‐rGO nanocomposite proved to feature an intrinsic peroxidase mimic activity, facilitating the oxidation of a peroxidase substrate like 3,3’,5,5’‐tetramethylbenzidine (TMB) with high efficiency to oxidised TMB (blue coloured product) with the aid of hydrogen peroxide (H2O2). The characteristic Michaelis‐Menten kinetics study allowed the establishment of the catalytic performance of AuAg‐rGO as an artificial enzyme. Glutathione (GSH) displays inhibiting effect on the oxidation of the peroxidase substrate, TMB. Therefore, AuAg‐rGO nanozyme was applied for detection of GSH and exhibited exceptional selectivity and sensitivity with a low limit of detection (LOD) of 38 nM within the 0–200 μM concentration range. The artificial nanozyme system reported here is simple, convenient, and straightforward for colorimetric sensing of GSH.

DFT supported experimental investigation of strain induced interfacial modification in Au-Ag bimetallic nanoparticles coated on activated sand

In this study, the strain induced modification in Au-Ag bimetallic nanoparticles (BNPs) coated on silica rich activated sand has been investigated. The coating of BNPs on activated sand modifies the interface as well as induces microstrain in the structure of the BNPs. The detailed investigation of the interfacial interaction of BNPs with silica in activated sand is performed by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and micro-Raman spectroscopy. Phonon confinement model has been employed to find out the insights of the Raman spectrum. The effect of microstrain induced in the nanoparticles is found to be influencing the catalytic efficiency significantly. The effectiveness as well as the kinetics and thermodynamics of the BNPs coated on activated sand has been studied for the catalytic reduction of an aromatic nitro compound usually present in wastewater. Density functional theory has also thrown light on the enhanced photocatalytic activity of the BNPs supported on activated sand and provides finer details of the electronic structure. Also, the supported BNPs can be conveniently recovered and reutilized multiple times without significant reduction in the catalytic efficiency.

Electrochemiluminescence biosensor for carcinoembryonic antigen detection based on Au-Ag/g-C3N4 nanocomposites

Herein, an electrochemiluminescence (ECL) aptasensor for carcinoembryonic antigen (CEA) detection was developed based on Au-Ag/g-C3N4 nanocomposites (NCs), which were synthesized by decorating graphitic carbon nitride (g-C3N4) nanosheets with alloy-structured Au-Ag bimetallic nanoparticles (NPs) via one-step in situ chemical reduction. As ECL sensing platform, Au-Ag/g-C3N4 NCs could significantly improve the ECL intensity of luminol due to the good conductivity of Au-Ag NPs, electrocatalytic activity for oxygen evolution reaction (OER) and the ability to adsorb luminol via π stacking interaction. In addition, it could load the thiol terminated aptamers of CEA via Au-S or Ag-S bonds. In the presence of CEA, the ECL response of the proposed biosensor decreased significantly due to the fact that the assembled protein layers hindered the electron transfer and the diffusion of ECL reactants toward the electrode surface. The proposed ECL sensor exhibited a good linear relationship with CEA in the range of 1.0–1.0 × 10−6 ng/mL with a detection limit of 8.9 × 10−7 ng/mL. The satisfactory results were obtained in the detection of CEA in human serum samples.

Formation and Removal of Alloyed Bimetallic Au–Ag Nanoparticles from Silicon Substrates for Tunable Surface Plasmon Resonance

Formation and Removal of Alloyed Bimetallic Au–Ag Nanoparticles from Silicon Substrates for Tunable Surface Plasmon Resonance

Bimetallic Au-Ag catalysts in HCHO catalytic oxidation: No synergetic effect?

We prepared AuAg bimetallic catalysts by sequential deposition method to study the role of Au and Ag in the HCHO catalytic oxidation behavior respectively. We found that the highest activity is found for Au monometallic catalyst, rather than AuAg bimetallic catalyst, which is related to the different HCHO oxidation reaction pathways over Au and Ag active sites from in situ DRIFTS results. In this work, different HCHO conversion pathways were found over the Au and Ag active sites, which consume the surficial OH groups and reactive oxygen species on the catalyst surface respectively, denoted as OH-assisted and Oa-assisted pathways. Au active site is dominated by the OH-assisted pathway because of its excellent activation ability to HCHO reaction intermediates. Ag active site is dominated by the Oa-assisted pathway because of its excellent activation ability to oxygen. In this paper, the catalytic behavior of AuAg bimetallic nanoparticles and the different role of Au and Ag active sites in reaction pathways in HCHO oxidation is clarified and discussed for the first time.

&lt;i&gt;Cocculus hirsutus&lt;/i&gt; Leaf Assisted Green Synthesis of Ag-Au Bimetallic Nanoparticles and their Antioxidant Properties

Bimetallic nanoparticles (BMNPs) of silver and gold are synthesized by eco- friendly green chemical procedure using leaf extract of Cocculus hirsutus. Under the experimental condition most individual silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) are spherical whereas silver-gold bimetallic nanoparticles (Ag-Au BMNPs) found cloudy and lost their individual shape. Ag-Au BMNPs formed by the co-reduction of Au(III) and Ag(I) ions in aqueous leaves extract solution where the extract act as both reducing and capping agent. NPs were characterized with the help of UV-Vis absorption spectroscopy, high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) analysis. UV-Vis spectroscopy exhibit surface plasmon absorption maxima at 435 and 540 nm for AgNPs and AuNPs respectively whereas surface plasmon resonance (SPR) maxima for Au-Ag bimetallic appeared in between the peaks corresponding to pure silver and gold at the same reaction conditions. X-ray diffraction analysis confirmed that crystalline nanoparticles (NPs) are face centered cubic structure. The synthesized bimetallic nanocomposites show stronger scavenging ability, around 67% and 75% on hydroxyl radical and superoxide radicals at the concentration of 400 µg/ml respectively, compared to the mono metallic AgNPs and AuNPs, indicating stronger antioxidant properties of Ag-Au BMNPs.

Surface-wrinkled SnO2 hollow microspheres decorated with AuAg bimetallic nanoparticles for triethylamine detection

Surface modification of metal oxides with bimetallic nanoparticles is regarded as an appealing way to improve the gas sensing properties. Herein, SnO2 hollow microspheres with wrinkle surface were synthesized, and were then decorated with Au, Ag, and bimetallic AuAg nanoparticles by immersing SnO2 into the solutions containing these as-prepared metal particles. Gas test results showed that the SnO2-AuAg displayed a higher response (61.3 to 100 ppm triethylamine at 240 °C), and shorter response/recovery time (4/24 s) than SnO2-Au (36.4, 5/26 s), SnO2-Ag (27.1, 5/32 s), and pure SnO2 (12.5, 6/37 s). Moreover, it showed excellent long-term stability. The surface chemical state of SnO2-AuAg were studied based on the experimental results. The mechanism of enhanced gas sensing performance was also proposed by the analysis of the morphological and structural composition, electronic and chemical sensitizations of Au and Ag, and the synergistic catalysis effect of AuAg bimetallic nanoparticles.

Simultaneous determination of aesculin and aesculetin and their interactions with DNA using carbon fiber microelectrode modified by Pt–Au bimetallic nanoparticles

Electrode sensitivity and selectivity in complex biological matrices are major challenges in the development of electrochemical sensors. Bimetallic nanoparticles provide a new perspective for enhancing electrocatalytic property because of some specific synergetic effects. In this work, platinum nanoparticles (PtNPs) and gold nanoparticles (AuNPs) modified carbon fiber microelectrode (PtNPs/AuNPs/CFME) was fabricated to determine aesculin and aesculetin simultaneously. Differential pulse voltammetry (DPV) method was conducted for the electrochemical sensing of aesculin and aesculetin, the modified electrode displayed high electrocatalytic activity for the redox of these two drugs. The linear ranges of aesculin and aesculetin were 0.4–10 μM and 0.04–1 μM, with the detection limits of 41 nM and 3.6 nM, respectively, which were the lowest values achieved. Furthermore, an electrochemical investigation of the interactions of these two drugs with Calf thymus double stranded DNA (dsDNA) was investigated by PtNPs/AuNPs/CFME, the decrease in peak currents is proportional to DNA concentration and can be used to detect DNA. The electrode was successfully used to measure aesculin and aesculetin in mouse serum and urine with 98.0–104.8% recovery. The novel electrochemical probe possessed excellent performances of high sensitivity, good reproducibility, and simplicity of fabrication, which will facilitate effective detection of aesculin and aesculetin for metabolic kinetics study.