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We have developed novel metal‐introduced and thiol‐modified silica‐coated magnetic beads (TM‐bead) and report their optical property. A total of six different types of Ag or Ag with Au introduced TM‐bead were prepared as follows: Ag was introduced onto TM‐bead either by immobilizing pre‐synthesized Ag nanoparticles (NPs) onto TM‐bead (TM‐bead@Ag NPs) or by growing Ag onto TM‐bead (TM‐bead@AgG). Subsequently, Au ions were introduced onto TM‐bead@Ag NPs (TM‐bead@Ag NPs@AuG) and TM‐bead@AgG (TM‐bead@AgG@AuG). Similarly, Au NPs were immobilized onto TM‐bead@Ag NPs (TM‐bead@Ag NPs&Au NPs) and TM‐bead@AgG (TM‐bead@AgG&Au NPs). The materials were analyzed by an UV–Vis spectroscopy, a scanning electron microscope and an energy‐dispersive X‐ray spectroscopy. Obtained under a unified frame, the results provide reliable and valid information against those types of metal based materials. The novel metal‐immobilized magnetic beads can also function as plasmonic tunable magnetic beads in biological, material, and chemical applications. [ABSTRACT FROM AUTHOR]

In the present work, a lamella from an Au—Ag aggregate found in Ni-laterites has been examined using Transmission Electron Microscope to produce a series of Precision Electron Diffraction (PED) patterns. The analysis of the structural data obtained, coupled with Energy Dispersive X-ray microanalysis, made it possible to determine the orientation of twinned native gold growing on the Au—Ag aggregate. The native Au crystal domains are found to have grown at the outermost part of the aggregate whereas the inner core of the aggregate is an Au—Ag alloy (∼4 wt% Ag). The submicron structural study of the natural occurring Au aggregate points to the mobilization and precipitation of gold in laterites and provides insights on Au aggregates development at supergene conditions. This manuscript demonstrates the great potential of electron crystallographic analysis, and in particular, PED to study submicron structural features of micron sized mineral aggregates by using the example of a gold grain found in a Ni-laterite deposits. [ABSTRACT FROM AUTHOR]

The results of thermobaric geochemical study of ores of the Dvoinoye epithermal Au-Ag deposit are considered. Study of the fluid inclusions has shown that the ores were formed from low-salinity hydrothermal solutions with Na, Ka, and Mg chlorides and CO2, HS-, CH4 trace fluxes at the time when the temperature dropped from 370 to 130°C. The results are compared with data obtained from the closely located Kupol and Sentyabr’skoye deposits. [ABSTRACT FROM AUTHOR]

Abstract: Efficient, stable, and low‐cost electrocatalysts for the degradation and sensing of environment pollutants are essential components of clean environment monitoring. Here we report, one‐step synthesis and characterization of 1–3 nm diameter sized bi‐metallic AuAg nanodots (NDs) embedded in amine functionalized silicate sol‐gel matrix (SSG) and its electrochemical studies toward nitrobenzene. The SSG was used as a reducing agent as well as stabilizer for the prepared mono‐ and bi‐metallic nanoparticles (NPs). From the HRTEM, STEM‐EDS and XPS analyses, the bi‐metallic AuAg NDs were identified as an alloy and not the mixtures of Au and Ag NPs. Characteristic surface plasmon resonance (SPR) band between the Au and Ag NPs SPR absorption region was noticed for the prepared AuAg NDs. The AuAg alloy NDs with different concentrations of Au and Ag (Au25Ag75, Au50Ag50 and Au75Ag25 NDs) modified electrodes exhibited synergistic electrocatalytic effect than did the Au and Ag NPs towards nitrobenzene reduction and detection. Together with ultra‐small size and exceptional colloidal stability features within these SSG‐AuAg NDs pave convenient way for nanotechnology‐based catalysts development and sensor applications. [ABSTRACT FROM AUTHOR]

The coalescence process at the initial stages has been investigated for the icosahedral and cuboctahedral Ag@Au clusters with 55 and 147 atoms supported on graphene and CNT surfaces. We have examined the different thermodynamics, dynamical, and structural properties of the supported clusters during the coalescence. Our results showed that the coalescence process makes the smaller cluster more stable than the bigger cluster and the smaller cluster experiences more coalescence than the bigger one. Also, the coalescence makes the cuboctahedral nanocluster more stable than the icosahedral cluster at the initial steps. The self-diffusion change is more significant for the icosahedral clusters than the cuboctahedral clusters at the initial steps. This result is in agreement with the total energy values and is due to the more tendency of the icosahedral structures to coalesce to be more stable than the cuboctahedral morphologies. [ABSTRACT FROM AUTHOR]

We describes the UV–visible spectroscopic and transmission electron microscopic evidence to the reactivity of Cu 2 + , and Ag + towards hydrazine for the synthesis of cetyltrimethylammonium bromide, CTAB, capped spherical hetero-structure and hexahedral Ag@Cu. The conventional techniques like, UV–visible, TEM, SEM, EDS, and FT-IR were used to the characterization. The catalytic reductive degradation of Rhodamine B (RB) by using Ag@Cu bimetallic nanoparticles as a catalyst has been reported for the first time in this study. The decrease in [RB] was monitored by UV–visible spectroscopy. The [Ag@Cu] = 6.6 × 10 − 5 mol dm − 3 exhibited remarkable catalytic activity towards [RB] = 3.5 × 10 − 5 mol dm − 3 in presence of [NaBH 4 ] = 1.3 × 10 − 3 mol dm − 3 , with a degradation efficiency of ca. 100% in 4 min. The experimental data revealed that the removal of RB increased with increasing the [catalyst loading] and [NaBH 4 ]. Apparent-first order rate constants, turnover frequency, activation parameters (E a , ΔH # , and ΔS # ) have been calculated and discussed. A possible mechanism for the de-colorization of RB has been proposed. [ABSTRACT FROM AUTHOR]

In this study, electrodynamic calculations were used to investigate the resonance light-scattering (RLS) properties of dielectric-Au-Ag double nanotube. It has been found that the scattering spectrum exhibits at most three pronounced RLS peaks in the visible region, and the RLS band number could be fine tuned by changing the dielectric constant of the inner dielectric wire. The outer dielectric surrounding also greatly affects the intensity and wavelength position of the RLS. The RLS with the longest wavelength (denoted as peak3) is always enhanced with the increase of the outer surrounding dielectric constant, i.e., ε . Whereas the ε -dependent scattering intensity change of RLS at middle wavelength becomes non-monotonous when the Ag-coating thickness is much smaller than that of Au wall. On the contrary, the ε -dependent scattering intensity change of RLS at shorter wavelength becomes non-monotonous when the Ag-coating thickness is much larger than that of Au wall. Although peak3 has a longer wavelength when the inner wire dielectric constant ε has a large value, the ε -dependent wavelength shift has been decreased; as the wavelength shift has been decreased, ε is increased. Similarly, although peak3 has a longer wavelength when the Ag coating has a small thickness, the ε -dependent wavelength shift has been decreased as the Ag-coating thickness is decreased. These calculating results about local dielectric environment-dependent RLS present a potential for design and fabrication of optical refractive index nanosensors based on light scattering. [ABSTRACT FROM AUTHOR]

The T,X-parameters of the main ore-forming stages of the Rogovik epithermal gold-silver deposit (northeastern Russia) were determined using microthermometric techniques on fluid inclusion assemblages. On the basis of these data we carried out thermodynamic calculations that model the formation conditions of three types of ore mineral assemblages: gold-silver – at the early volcanic stage, silver-polymetallic and silver-gold-polymetallic – at the late volcanoplutonic stage. The silver-gold-polymetallic mineralization is located at the sites where silver-polymetallic and gold-silver zones overlap. The calculations were made using the “Selektor-C” software within a complex geochemical multicomponent system. Several scenarios of formation of gold-silver mineralization at an early volcanic stage were considered: 1) boiling of a hydrothermal solution; 2) interaction of residual aqueous solution with host rocks; 3) mixing of an ore-bearing gas phase with meteoric waters. For the late volcanoplutonic stage, we modeled formation of “silver mineralization” using an ore-forming solution genetically related to a deep-seated granite massif and its interaction with host rocks and gold-silver zones of early volcanic stage. These physicochemical models substantially improve our understanding of formation of the three types of mineral assemblages at the Rogovik deposit and can be applied to other epithermal deposits with similar mineralization styles. [ABSTRACT FROM AUTHOR]

Bimetallic core-shell nanostructures have been attracted tremendous attention due to their ability to form novel materials with unique chemical, optical, and physical properties. Here, we have studied the influence of core size of Au/Ag bimetallic core-shell nanostructures on the Raman enhancement efficiency with the Raman-active probe methylene blue. The surface-enhanced Raman scattering intensity is increased with increase in the core size of Au/Ag bimetallic core-shell nanoparticles. Interestingly, the enhancement factor is found to be 6.58 × 10 for the Au/Ag core-shell nanoparticles and allows easy detection of analyte methylene blue. Thus, surface-enhanced Raman scattering properties of the metal nanoparticles are significantly enhanced due to the Au/Ag core-shell structures and the enhancement factor is dependent on the size of the core of the bimetallic nanoparticles. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Surface tension calculation of the binary alloys Ag–Au at the temperature of 1381 K, where Ag and Au have similar electronic structures and their atomic radii are comparable, are carried out in this study using several equations over entire composition range of Au. Apparently, the deviations from ideality of the bulk solutions, such as activities of Ag and Au are small and the maximum excess Gibbs free energy of mixing of the liquid phase is for instance −4500 J/mol atXAu= 0.5. Besides, the results obtained in Ag–Au alloys that at a constant temperature the surface tension increases with increasing composition while the surface tension decreases as the temperature increases for entire composition range of Au. Although data about surface tension of the Ag–Au alloy are limited, it was possible to make a comparison for the calculated results for the surface tension in this study with the available experimental data. Taken together, the average standard error analysis that especially the improved Guggenheim model in the other models gives the best agreement along with the experimental results at temperature 1383 K although almost all models are mutually in agreement with the other one. [ABSTRACT FROM PUBLISHER]

The synthesis and structure determination of atomically precise alloy nanoclusters have attracted much attention in recent research. Herein, we report a new alloy nanocluster Au 24- x Ag x (TBBM) 20 ( x ∼ 1) synthesized via a ligand-exchange-induced size/structure transformation method. Its X-ray structure is obtained successfully and the dopant Ag is found to occupy three special positions in the kernel, rather than equivalently over all the kernel sites. This selective occupancy is interesting and DFT calculation results suggest that the relative oxidation state (rationalized as difference in the charge) of the Ag when doped into the cluster is likely determining the most favorable doping positions. This work provides a new strategy for controlled synthesis of new Au-Ag nanoclusters and also reveals a new scenario for the doping position of Ag atoms in Au-Ag bimetal nanoclusters. [ABSTRACT FROM AUTHOR]

A high quality graphene-encapsulated AuAg alloy (AuAg-GR) nanohybrid with homogeneous structure and good reproducibility over a desired area was successfully fabricated. Taking benefits of the unique architecture, such nanohybrid was employed as an efficient electrocatalyst for sensing application. The AuAg-GR based sensor could sensitively detected neurotransmitter serotonin (5-HT) with wide linear detection range (2.7 nM to 4.82 μM), very low detection limit (1.6 nM), negligible interference, and excellent reproducibility. In addition, AuAg-GR based sensor accurately determined 5-HT in human serum samples. This is due to the enhanced catalytic activity of GR nanosheets-encapsulated AuAg nanostructures, which possessed well monodispersion of AuAg alloy, greater electrochemical active sites, and good charge transfer possibility. The obtained results imply that such nanohybrid is a potential candidate for synthesizing electrochemical sensors in requirement of high sensitivity, long-term stability, and good reproducibility. [ABSTRACT FROM AUTHOR]

The outstanding chemical stability of Au and intense localized surface plasmon resonance of Ag make it possible to obtain a nanostructure with a good balance of good chemical stability and optical response. In this paper, we investigated the relationship between optical properties and the composition and size of Ag-Au alloy nanoparticle with numerical calculation by applying experimental data. Simplified empirical formulas are proposed through numerical simulation. The properties of extinction efficiency and the relative contribution of scattering and absorption efficiency to the extinction efficiency have been researched in detail. The calculated result and experimental data has been compared, and good agreement is obtained. Our work contributes greatly to catalysis application of Au-Ag alloy NPs in specific regions. [ABSTRACT FROM AUTHOR]

Despite a significant surge in the number of investigations into chirality at the nanoscale, especially thiolated chiral molecules capping gold clusters, only limited knowledge is currently available to elaborate the alloying effect on chiroptical behavior of bimetallic nanoparticles (NPs). Also, few successful cases as to the efforts toward the development of chirality-dependent applications on the optically active nanomaterial have been made. Herein, as a positive test case for chiral alloy nanoparticle synthesis, the stable and large chiroptical ultrafine Au-Ag alloy NPs were prepared by reduction of different molar fractions of HAuCl4 and AgNO3 with NaBH4 in the presence of d/l-penicillamine (d/l-Pen). Compared with those of monometallic Au and Ag counterparts with comparable size, the Au-Ag alloy NPs (Ag mole fraction, 70%) obviously displayed the largest optical activities with the maximum g-factors of ~1.6 × 10-3. Impressively, the Pen-mediated synthesis of chiral Au-Ag alloy NPs possesses a colorimetric self-recognition function and can be used as an incisive circular dichroism (CD) probe toward d- and l-Pen enantiomers. The plasmonic CD signal amplification (ΔICD) shows good linearity with the amount of Pen over the range of 5.0-80.0 μM with a detection limit (3σ) of 1.7 μM for l-Pen and 1.5 μM for d-Pen, respectively. In addition, the sensing system exhibits good selectivity toward d- and l-Pen in the presence of other enantiomers; therefore, it is highly expected that the approach described here would open new opportunities for design of more novel enantioselective analyses of important species related to biological processes. [ABSTRACT FROM AUTHOR]

New data on mercurial mineralization are presented, and a detailed characteristic is given for the first discovery of mercurous silver in ores of the Rogovik gold-silver deposit (the Omsukchan trough, Northeastern Russia). It was found that native silver in the examined ores occurs as finely-dispersed inclusions in quartz filling microcracks and interstitions. It also occurs in associations with kustelite, Ag sulfosalts and selenides, selenitic acanthite, and argyrodite. The mercury admixture varies from 'not detected' in the central parts of grains to 0.22-1.70 wt % along the edges, or, in independent grains, to the appearance of Ag amalgams containing 10.20-24.61 wt % of Hg. The xenomorph form of grains of 50 μm or less in size prevails. It is assumed that the appearance of mercurial mineralization is caused by the superposition of products of the young Hg-bearing Dogda-Erikit belt upon the more ancient Ag-bearing Omsukchan trough. [ABSTRACT FROM AUTHOR]

The well-known AuAg nanohybrid system was effectively synthesized, utilizing polyvinyl pyrrolidone (PVP) as a multiple metal precursor reducing agent (based solely on their reduction potentials), thereby drastically decreasing their activation energy of diffusion and readily facilitating the homogenous alloy nanoparticle formation, duly confirmed by Vegard's law. Furthermore, the crucial parameters in determining the local electric field enhancement in the vicinity of the alloy nanoparticles such as the quality factor Q, dephasing time, T2 and the homogenous line width Γ were also evaluated in a systematic manner, in correlation with their unique visible optical absorption spectra. Optical band gap calculations of this robust AuAg/PVP nanocomposite system demonstrate the formation of trap levels between the HOMO and LUMO energy states with increasing Urbach's energy for decreasing Au content. The surface enhanced infrared (SEIRA) measurements with the analyte bromophenol, not only highlight the differential metal–PVP–analyte binding, but also corroborate the optical constants of the nanohybrids. Moreover, the catalytic conversion of 4-nitro-aniline (4-NA) to p-phenylenediamine (p-PDA) in the presence of AuAg nanohybrids visibly distinguishes their excellent stability and reproducibility along with their moderate rate constant in direct contrast to the poor recycling ability of their individual metal counterparts. [ABSTRACT FROM AUTHOR]

Rare phases of the Au-Ag-Sb system were recognized in the Krásná Hora Sb-Au deposit (Sb 1.5-3 wt.%; Au 3-5 ppm), Czech Republic which correspond to auriferous dyscrasite (up to 7 at.% Au), auriferous allargentum (up to 34 at.% Au), and an unnamed phase with composition similar to the eutectics (E1, E2) of the experimental Au-Ag-Sb system. The dominant ore mineral is stibnite with rare native antimony, native gold and a Ag-Au alloy. Textural relationships are well established: stibnite (early)→gold→aurostibite→ native antimony (late). Gold is present in four generations: Au-1 (0-15 at.% Ag) is the most abundant type; Au-2 (20-70 at.% Ag) forms thin rims along intra-grain boundaries of Au-1; Au-3 and Au-4 are rare and almost pure (∼0 at.% Ag). The formation of most of the Au-2 and of Au-Ag-Sb phases is associated with Ag-mobilization coupled with the Au-1 to aurostibite transformation via dissolution-precipitation and solid-state diffusion processes at temperatures <200°C. [ABSTRACT FROM AUTHOR]

This article reports a general approach to the facile synthesis of M@Au/Ag (M = Au, Pd, and Pt) nanorattles. The synthesis involves three major steps: (i) formation of M@Ag nanocubes via seed-mediated growth, (ii) conformal deposition of ultrathin Au shells on the M@Ag nanocubes by reducing HAuCl4 with ascorbic acid under an alkaline condition, and (iii) formation of M@Au/Ag nanorattles through a galvanic replacement reaction between the Ag shells and aqueous HAuCl4. The deposition of an ultrathin Au shell prior to the galvanic replacement reaction is crucial to a successful synthesis as this shell can enhance the mechanical strength of the resultant nanorattles by preventing the Au/Ag alloy shell from fragmentation during the galvanic replacement process. The localized surface plasmon resonance peak of the nanorattles is determined by the thickness of the Au/Ag alloy shell. For Au@Au/Ag nanorattles with an edge length of 15 nm, they could be tuned to have near-infrared absorption and excellent photothermal conversion capability for their use as transducers in the effective destruction of cancer cells through laser irradiation. [ABSTRACT FROM AUTHOR]

Studies on localized surface plasmon resonance (LSPR) of noble metals (mainly gold and silver) regarding solar-driven photocatalysis have been attracting enormous interests over the past two decades. As research on LSPR continues to expand, recently, aluminum (Al) with respect to plasmonic enhanced photocatalysis beyond such noble metals has attracted considerable attention. Al as an abundant and relatively inexpensive metal holds great promise for plasmonic photocatalysis with outstanding light-harvesting capacity and performance in virtue of its unique optical characteristics. Herein, a short review is given on the related basics of LSPR, and the key factors including the size, shape, and oxide formation of Al nanostructures, which significantly influence the optical response of Al. In particular, photocatalytic applications in artificial photoredox processes with regard to plasmonic Al are outlined. In addition, some perspectives on the opportunity and challenge for future development of this research field are offered. [ABSTRACT FROM AUTHOR]

The graphene-mediated surface enhanced Raman scattering (SERS) substrates by virtues of plasmonic metal nanostructures and graphene or its derivatives have attracted tremendous interests which are expected to make up the deficiency of traditional plasmonic metal substrates. Herein, we designed and fabricated a novel ternary Ag@GO@Au sandwich hybrid wherein the ultrathin graphene oxide (GO) films were seamlessly wrapped around the hierarchical flower-like Ag particle core and meanwhile provided two-dimensional anchoring scaffold for the coating of Au nanoparticles (NPs). The surface coverage density of loading Au NPs could be readily controlled by tuning the dosage amount of Au particle solutions. These features endowed the sandwiched structures high enrichment capability for analytes such as aromatic molecules and astonishing SERS performance. The Raman signals were enormously enhanced with an ultrasensitive detection limit of rhodamine-6G (R6G) as low as 10 −13 M based on the chemical enhancement from GO and multi-dimensional plasmonic coupling between the metal nanoparticles. In addition, the GO interlayer as an isolating shell could effectively prevent the metal–molecule direct interaction and suppress the oxidation of Ag after exposure at ambient condition which enabled the substrates excellent reproducibility with less than 6% signal variations and prolonged life-time. To evaluate the feasibility and the practical application for SERS detection in real-world samples based on GO sandwiched hybrid as SERS-active substrate, three different prohibited colorants with a series of concentrations were measured with a minimum detected concentration down to 10 −9 M. Furthermore, the prepared GO sandwiched nanostructures can be used to identify different types of colorants existing in red wine, implying the great potential applications for single-particle SERS sensing of biotechnology and on-site monitoring in food security. [ABSTRACT FROM AUTHOR]

Large aspect ratio bimetallic nanowire structures comprise potential applications in areas such as higher catalytic activity and surface Raman enhancement spectroscopy (SERS) substrates. By using the highly anisotropic ultra-clean Si(110) surface and with initial growth of sub monolayer (ML) Ag on such surface, a high aspect ratio AuAg bimetallic nanostructures can be formed. We report on the formation of large aspect ratio (>7.2 ± 0.8) AuAg nanowires on ultra-clean Si(110) surfaces using 0.5 ML Ag followed by 3.0 ML Au using molecular beam epitaxy (MBE) at a growth temperature of 300 °C. Under similar growth conditions without pre-deposition of Ag and only with deposition of 3.0 ML of Au consequences smaller aspect ratio (2.1 ± 0.1) monometallic Au nanostructures. The enhancement in aspect ratio of the nanostructures is attributed to the formation of one dimensional Ag layer (prior to Au growth) and Au-Ag bimetallic intermixing at elevated temperature. Considering deposition of 3.0 ML Au, a regime of substrate temperature ≈ 270–330 °C is found to be optimum to growth some of high aspect ratio (>25.0) AuAg nanowires as well. Exterior of this regime, at lower temperature due to low mobility of the ad-atoms and at higher temperature due to probable inter-diffusion of Ag, such extremely high aspect ratio AuAg nanowires found to be infrequent to grow. For growth at substrate temperature 300 °C, mean aspect ratio of the AuAg nanostructures is gradually increased in accordance with Au thickness up to 3.0 ML due to preferential accumulation of ad-atoms (Au, Ag) along Si 〈 1 1 ¯ 0 〉 and thereafter reduces for adequate accumulation along Si 〈 001 〉 . [ABSTRACT FROM AUTHOR]

In this work, we report on an efficient approach to fabricating large-area and uniform planar arrays of highly ordered nanoporous gold nanowires. The approach consists in dealloying Au-Ag alloy nanowires in concentrated nitric acid. The Au-Ag alloy nanowires were obtained by thermal annealing at 800 °C for 2 h of Au/Ag stacked nanoribbons prepared by subsequent evaporation of silver and gold through a nanograted photoresist layer serving as a mask for a lift-off process. Laser interference lithography was employed for the nanopatterning of the photoresist layer to create the large-area nanostructured mask. The result shows that for a low Au-to-Ag ratio of 1, the nanowires tend to cracks during the dealloying due to the internal residual stress generated during the dealloying process, whereas the increase of the Au-to-Ag ratio to 3 can overcome the drawback and successfully leads to the obtainment of an array of highly ordered nanoporous gold nanowires. Nanoporous gold nanowires with such well-regulated organization on a wafer-scale planar substrate are of great significance in many applications including sensors and actuators. [ABSTRACT FROM AUTHOR]

Peptide based methods create new revenues to fabricate stable, multifunctional noble metal nanomaterials under mild and green synthesis conditions. Peptide sequence A4 stabilized AuAg alloyed nanomaterials were fabricated through a facile and straightforward approach. The as-prepared alloyed nanomaterials demonstrated effective catalytic activity toward oxygen electroreduction in alkaline media. Both the metal-to-A4 ratio and Au-to-Ag ratio were optimized to enrich the electrocatalytic performance, and the sample of Au:Ag:A4 = 10:30:1 exhibited the highest activity among the series. The performance of Au:Ag:A4 = 10:30:1 is comparable with that of commercial Pt/C, within the context of onset potential, diffusion-limited current density as well as long-term stability. The as-prepared samples were characterized by UV–visible absorbance, transmission electron microscopy (TEM), as well as X-ray photoelectron microscopy (XPS). The improved activity is probably attributed to the alloying induced ensemble effects and electronic effects. This discovery may shed light on fabricating peptide based alloys as highly efficient catalysts with enhanced stability for oxygen reduction reaction (ORR). [ABSTRACT FROM AUTHOR]

Large, stable and single domain unit cell with row-like structures makes reconstructed Si(5 5 12) surface an important one-dimensional growth template of nanostructures. We report on the morphological aspects of the growth of AuAg bimetallic nanostructures on a reconstructed Si(5 5 12) surface that has been deposited with a 0.5 monolayer (ML) Ag and various Au thicknesses (0.5 to 5.0 ML) to determine the optimum gold thickness for a growth of high aspect ratio of AuAg nanostructures. The mean aspect ratio of AuAg nanostructures increases up to Au thickness of 3.0 ML and for larger thickness the mean aspect ratio decreases. The prior growth of 0.5 ML Ag on reconstructed surface result in the formation of one-dimensional Ag strips which are helping for preferential nucleation sites along Si $$\left\langle 1\bar{1}0 \right\rangle$$ to form AuAg bimetallic long aspect ratio structures. Followed by these early processes of growth, for Au thickness >3.0 ML, excess Au ad-atoms begin to accumulate along Si $$\left\langle 66\bar{5} \right\rangle$$ and consequences reduction of mean aspect ratio of bimetallic nanostructures. Nanostructures are grown using molecular beam epitaxy method under ultra-high vacuum conditions and in situ scanning tunneling microscopy has been used to investigate the morphological variations. Determination of structural aspects and compositional analysis has been carried out using Rutherford backscattering spectrometry and high-resolution (scanning) transmission electron microscopy methods. [ABSTRACT FROM AUTHOR]

Nanoporous Au attracts great technological interest and it is a promising candidate for optical and electrochemical sensors. In addition to nanoporous Au leafs and films, recently, interest was focused on nanoporous Au micro- and nano-structures on surfaces. In this work we report on the study of the characteristics of nanoporous Au structures produced on surfaces. We developed the following procedures to fabricate the nanoporous Au structures: we deposited thin Au/Ag bilayers on SiO 2 or FTO (fluorine-doped tin oxide) substrates with thickness x Au and x Ag of the Au and Ag layers; we induced the alloying and dewetting processes of the bilayers by furnace annealing processes of the bilayers deposited on SiO 2 and by laser irradiations of the bilayers deposited on FTO; the alloying and dewetting processes result in the formation of Au x Ag y alloy sub-micron particles being x and y tunable by x Au and x Ag . These particles are dealloyed in HNO 3 solution to remove the Ag atoms. We obtain, so, nanoporous sub-micron Au particles on the substrates. Analyzing the characteristics of these particles we find that: a) the size and shape of the particles depend on the nature of the dewetting process (solid-state dewetting on SiO 2 , molten-state dewetting on FTO); b) the porosity fraction of the particles depends on how the alloying process is reached: about 32% of porosity for the particles fabricated by the furnace annealing at 900 °C, about 45% of porosity for the particles fabricated by the laser irradiation at 0.5 J/cm 2 , in both cases independently on the Ag concentration in the alloy; c) After the dealloying process the mean volume of the Au particles shrinks of about 39%; d) After an annealing at 400 °C the nanoporous Au particles reprise their initial volume while the porosity fraction is reduced. Arguments to justify these behaviors are presented. [ABSTRACT FROM AUTHOR]

Two analytical models are proposed to represent the dielectric function of the Ag x Au 1-x alloys. The intraband effects are represented by the Drude model whereas interband transitions are modelled by means of either Lorentzian-pole pairs or critical-point terms. Quantitative comparisons are presented to show that, for all the alloy compositions, both models describe very well the experimental data reported by Peña-Rodríguez et al. [Opt. Mater. Express 4 (2014) 403–410] in the energy region between 0.65 and 6.6 eV. Accuracy of the critical-point terms is considerably better but Lorentzian-pole pairs can be easier to integrate in existing FDTD software. [ABSTRACT FROM AUTHOR]

Fluorescent CS/Ag-Au (chitosan/silver-gold) nanocomposite containing different weight percentage of Ag and Au was synthesized using the chemical reduction method. 5-Fluorouracil (5-FU) encapsulated nanocomposite was also synthesized and its cytotoxicity towards breast cancer cell lines (MCF-7) studied. The XRD pattern of the nanocomposite shows peaks of chitosan, silver and gold. The peaks corresponding to gold and silver indicate the face centered cubic structure of silver and gold nanoparticles. The polymer matrix nanocomposite structure with chitosan as the matrix and silver-gold as the filler phase is evident from the high resolution transmission electron microscopy (HRTEM) images and an increase in particle size from∼5 nm to about 12 nm is noticeable on encapsulation of 5-Fluorouracil (5-FU). The presence of fluorine in the case of 5-FU encapsulated nanocomposite and the presence of reflections corresponding to 5-FU in the SAED pattern confirms the encapsulation of 5-FU into the nanocomposite, which is also confirmed by elemental mapping. The presence of a single surface plasmon resonance (SPR) peak in the case of the nanocomposite in a position in between the SPR bands of pure silver and gold nanoparticles confirms the formation of Ag-Au alloy and the elemental mapping results obtained for the nanocomposite also supports the UV–vis results. The photoluminescence (PL) spectrum clearly shows an emission peak in the near infrared region (700–900 nm), which makes the nanocomposite suitable for use in cellular imaging. The application of the nanocomposite as a colorimetric sensor was also studied and it was found to be useful for the specific detection of mercury (Hg) without much interference and the detection limit was found to be 5.0 × 10 −8 M. [ABSTRACT FROM AUTHOR]

Silver nanoprisms (Ag-PRs) have been epitaxially edge-coated with gold and subsequently covered fully with P3HT chains to fabricate poly(3-hexylthiophene)-grafted edge-gold-coated silver nanoprisms (P3HT@AuAg-PRs) which are miscible with organic solvents; each AuAg-PR with a typical edge length of 122 nm is surrounded by 4.4 × 103 P3HT chains. Both absorption and emission spectra have indicated that aggregated P3HT chains are bound on the surfaces of noble-metal nanoprisms. Picosecond emission kinetic profiles have suggested that the S1 relaxation time of P3HT in P3HT@AuAg-PRs is reduced due to energy transfer to AuAg-PRs. From nanosecond transient-absorption kinetic profiles, the reduced amplitude and the increased decay time of T1 excitons in P3HT@AuAg-PRs have been measured, indicating that neither the intersystem crossing of S1 into T1 nor the intersystem crossing of T1 into S0 occurs effectively in P3HT@AuAg-PRs owing to the stretched and rigid conformations of P3HT chains bound on the surfaces of AuAg-PRs. The surface-enhanced Raman scattering effect of P3HT@AuAg-PRs is as high as 4.6 because the sharp tips of AuAg-PRs which are maintained via gold coating serve as “hot spots”. The morphology deformation time of P3HT@AuAg-PRs in H2O2(aq) has been extended 48 times longer than that of Ag-PRs. Overall, our fabricated nanocomposites of P3HT@AuAg-PRs not only have feasible-process ability but also possess enhanced optical properties and high stability against oxidizing agents, extending the use of noble-metal nanoprisms for various optical applications. [ABSTRACT FROM AUTHOR]

Nanogap between two metallic nanostructures has been demonstrated to be able to efficiently concentrate an incident electromagnetic field into a small space. As a result, the formed strong field localization could extraordinarily enhance the surface-enhanced Raman scattering (SERS). In this study, controllable plasmonic nanogaps are formed by separating two layers of plasmonic Ag nanoparticles (50–100 nm) with small Au nanoparticles (2.5–6 nm). The size of the nanogaps can be readily tuned by altering the size of the Au nanoparticles. Utilizing an SERS substrate with such nanogaps, the SERS performance can be significantly improved. Such improvement could be attributed to the strongly enhanced electric field within the nanogaps, which is demonstrated by the Finite-difference time-domain simulations. The present work provides a facile strategy to rationally fabricate SERS substrates with controllable nanogaps and intensified SERS signals. [ABSTRACT FROM AUTHOR]

One-step gamma radiation assisted method has been used for the synthesis of Silver-Gold (Ag-Au) alloy nanoparticles with simultaneous reduction of graphene oxide (GO). UV–vis spectroscopic results along with X-ray diffraction analysis, X-ray Photoelectron spectroscopy and Transmission electron microscopy confirmed the decoration face centered cubic structured Ag-Au nanoparticles of size (5–19) nm on reduced graphene oxide (rGO) sheets. The increase in disorder parameter in Raman spectroscopy indicates the formation of more number of small sp 2 domains. The synthesized Ag-Au-rGO nanocomposite showed enhanced catalytic activity towards the reduction of 4-Nitrophenol compared to individual Ag-Au and rGO components. [ABSTRACT FROM AUTHOR]

The structural and optical properties of DNA-mediated Au-Ag Janus nanostructures (JNs) are comprehensively studied by X-ray and optical techniques. The theoretical model for small angle X-ray scattering of Au-Ag JNs is proposed, and the fitting process is outlined. A hybrid junction consists of DNA and Ag is introduced in order to reconcile the discrepancy between the experimental and simulated optical spectra of Au-Ag JNs. The physical origins and controlling factors of the localized surface plasmon resonance modes are determined, which lay the foundations for managing and exploiting the unique plasmonic properties of Au-Ag JNs. [ABSTRACT FROM AUTHOR]

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 λ max = ∼550, 450 and 500 nm 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 (∼10–50 nm) 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. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman spectroscopy (SERS) is a powerful tool with high potential for multiplexed detection of dilute analytes. However, quantitative SERS of kinetic assays can be difficult due to the variation in enhancement factors caused by changing reaction conditions. We report a method for quantitative SERS kinetic analysis using colloidal Ag–Au core–shell nanocubes (Ag@AuNCs) as the SERS substrate. This substrate is mass producible, possesses large SERS enhancement, and is resistant to degradation in most environments. The SERS enhancement of the Ag@AuNCs was evaluated both experimentally and computationally. Quantitation was achieved by covalently attaching a non-reactive internal standard (IS) to substrate surfaces and normalizing SERS spectra to the IS signal. We demonstrated that IS normalization corrects for temporal variations in enhancement factor and particle concentration. Quantitation was demonstrated by monitoring the base-catalyzed aldol condensation of surface-bound 4-(methylthio)benzaldehyde with free acetone. The kinetic model of this reaction was fitted to IS normalized SERS data, resulting in kinetic parameters that agreed well with published values. This SERS platform is a robust and sensitive method for quantitative analysis of kinetic assays, with potential applications in many fields. [ABSTRACT FROM AUTHOR]

The well-dispersed nanoparticles of Au-Ag alloys on graphitic carbon nitride (g-C 3 N 4 ), with varying ratios of Au, were synthesized by a facile route. The diffuse reflectance spectroscopy (DRS) verified the upsurge in the intensity of characteristic surface plasmonic resonance (SPR) absorption bands with the increasing Au contents. The photoluminescence (PL) spectroscopy estimated the role of surface dispersed Au-Ag alloy NPs on the luminescence properties of g-C 3 N 4 and the suppression the probable recombination of photo-generated excitons. The structural characterization by XRD and morphological assessment by SEM revealed the uniform dispersion of Au-Ag alloy nanoparticles on the surface of g-C 3 N 4 whereas XPS analysis endorsed the presence of Au and Ag in metallic form. The HRTEM analysis confirmed the homogeneous distribution of Au and Ag contents in the alloys. The photocatalytic activity of the Au-Ag/g-C 3 N 4 was evaluated in the exposure of natural sunlight and artificial visible light for the degradation of dye substrate and compared with that of g-C 3 N 4 , Ag/g-C 3 N 4 and Au/g-C 3 N 4 . The Au-Ag alloy modified g-C 3 N 4 photocatalysts exhibited significantly higher activity for the decolorization of Rhodamine B in the visible light as compared to pure, Ag and Au loaded g-C 3 N 4 that signified the contributing role of SPR in the degradation process. The individual role of SPR in the photocatalytic process was also verified by using monochromatic (532 nm) visible laser light. The mineralization ability of the synthesized alloy catalysts was estimated by TOC removal efficiency. The kinetics of the degradation/mineralization processes under various experimental conditions was also evaluated. [ABSTRACT FROM AUTHOR]

We study a single isolated Ag–Au nanowire with a nanofocused X-ray beam combining coherent diffraction methods in both forward scattering and diffraction geometries. X-ray scattering tomography measurements in forward geometry reveal a core–shell structure and allow determining the external size and shape of the nanowire. Bragg geometry measurements reveal the internal structure of the nanowire, notably the presence of stacking-faults in the nanowire. [ABSTRACT FROM AUTHOR]

We benchmark existing and improved self-consistent-charge density functional based tight-binding (SCC-DFTB) parameters for silver and gold clusters as well as for bulk materials. In the former case, our benchmarks focus on both the structural and energetic properties of small-size AgN and AuN clusters (N from 2 to 13), medium-size clusters with N = 20 and 55, and finally larger nanoparticles with N = 147, 309, and 561. For bulk materials, structural, energetics and elastic properties are discussed. We show that SCC-DFTB is quite satisfactory in reproducing essential differences between silver and gold aggregates, in particular their 2D-3D structural transitions, and their dependency upon cluster charge. SCC-DFTB is also in agreement with DFT and experiments in the medium-size regime regarding the energetic ordering of the different low-energy isomers and allows for an overall satisfactory treatment of bulk properties. A consistent convergence between the cohesive energies of the largest investigated nanoparticles and the bulk's is obtained. On the basis of our results for nanoparticles of increasing size, a two-parameter analytical extrapolation of the cohesive energy is proposed. This formula takes into account the reduction of the cohesive energy for undercoordinated surface sites and converges properly to the bulk cohesive energy. Values for the surface sites cohesive energies are also proposed. [ABSTRACT FROM AUTHOR]

The current study demonstrates a potential method for maximum utilization of the entire visible light region of the solar spectrum by designing a plasmonic-metals semiconductor composite. A combination of Ag+Au nanoclusters would broaden the visible-light absorption at least between 400 and 650 nm. This hypothesis was evaluated through solar water splitting (SWS) activity of Au-TiO2, Ag-TiO2, and Ag on Au-TiO2 (AgAuT) composites. AgAuT bimetallic nanocomposite shows the maximum apparent quantum yield of 3.3 % with hydrogen generation (718 μmol h.g−1) from aqueous methanol, and overall water splitting activity (7 μmol g.h−1, AQY=0.04 %) under one sun conditions. Enhanced photocatalytic activity of AgAuT is partly attributed to the formation of hot electrons. A thin layer of Ag coating on Au particles leads to a core-shell morphology with Au in the core. Fermi level equilibration between metal and titania, and Schottky junction formation are directly demonstrated. The strong electronic interaction between Ag and Au, and with TiO2 is evident from its electron rich character and confirmed by Raman spectroscopy, X-ray photoelectron spectroscopy, photoluminescence, and high-resolution TEM measurements. Electronic factors seem to be responsible for the high rate of hydrogen production. [ABSTRACT FROM AUTHOR]

Silica-coated gold-silver alloy nanoshells were obtained via a bioinspired approach using gelatin and poly-l-lysine (PLL) as biotemplates for the interfacial condensation of sodium silicate solutions. X-ray photoelectron spectroscopy was used as an efficient tool for the in-depth and complete characterization of the chemical features of nanoparticles during the whole synthetic process. Cytotoxicity assays using HaCaT cells evidenced the detrimental effect of the gelatin nanocoating and significant induction of late apoptosis after silicification. In contrast, PLL-modified nanoparticles had less biological impact that was further improved by the silica layer, and uptake rates of up to 50% of those of the initial particles could be achieved. These results are discussed considering the effect of nanosurface confinement of the biopolymers on their chemical and biological reactivity. [ABSTRACT FROM AUTHOR]

In this article, the photophysical and nonlinear optical (NLO) characterizations of diaminopyrimidin-2-ylthio phthalocyaninatozinc (II) ( 2 ) before and after conjugation to Ag x Au y nano-alloys are discussed. Phthalocyanines-Ag x Au y ( 2 -Ag x Au y ) composites showed enhanced triplet state and nonlinear optical behaviour when compared to free phthalocyanine. Optical limiting (OL) responses of the samples were evaluated using Z-scan technique at 532 nm and 10 ns in dimethyl sulfoxide. Reverse saturable absorption (RSA), which is a direct consequence of triplet absorption of already excited molecules was observed as the dominant mechanism responsible for nonlinearity of the samples. By virtue of the magnitude of absorption coefficients and other NLO optical parameters estimated in this work, 2 -Ag x Au y composites were found to exhibit stronger optical limiting responses than unconjugated phthalocyanine. The large third-order susceptibilities of the composites make them suitable materials for attenuating modern laser radiations, and also found useful in various optical applications. [ABSTRACT FROM AUTHOR]

Recently, nanoporous metal prepared by dealloying is sought for promising applications in catalysis, electronics, optic and drug delivery, due to its unique porous structure and property. Extending the facile method to prepare novel nanoporous material, further investigating its structure, and exploring its applications are very important to nanomaterial and industry field. Here we fabricate several nanoporous materials based on the dealloying process. The structure and possible formation mechanism are also investigated. Moreover, we explore their applications for the selective oxidation of alcohols. [ABSTRACT FROM AUTHOR]

Herein, gold-silver bimetallic nanoclusters (Au-Ag NCs) with the high fluorescent intensity were first synthesized successfully and utilized for the fabrication of sensitive and specific sensing probes toward inorganic pyrophosphatase (PPase) activity with the help of copper ion (Cu2+) and inorganic pyrophosphate ion (PPi). Cu2+ was used as the quencher of fluorescent Au-Ag NC, while PPi was employed as the hydrolytic substrate of PPase. The system consisted of PPi, Cu2+ ion, and bovine serum albumin (BSA)-stabilized Au-Ag NC. The detection was carried out by enzyme-induced hydrolysis of PPi to liberate copper ion from the Cu2+-PPi complex. In the absence of target PPase, free copper ions were initially chelated with inorganic pyrophosphate ions to form the Cu2+-PPi complexes via the coordination chemistry, thus preserving the natural fluorescent intensity of the Au-Ag NCs. Upon addition of target PPase into the detection system, the analyte hydrolyzed PPi into phosphate ions and released Cu2+ ion from the Cu2+-PPi complex. The dissociated copper ions readily quenched the fluorescent signal of Au-Ag NCs, thereby resulting in the decrease of fluorescent intensity. Under optimal conditions, the detectable fluorescent intensity of the as-prepared Au-Ag NCs was linearly dependent on the activity of PPase within a dynamic linear range of 0.1-30 mU/mL and allowed the detection at a concentration as low as 0.03 mU/mL at the 3sblank criterion. Good reproducibility (CV < 8.5% for the intra-assay and interassay), high specificity, and long-term stability (90.1% of the initial signal after a storage period of 48 days) were also received by using our system toward target PPase activity. In addition, good results with the inhibition efficiency of sodium fluoride were obtained in the inhibitor screening research of pyrophosphatase. Importantly, this system based on highly enhanced fluorescent Au-Ag NCs offer promise for simple and cost-effective screening of target PPase activity without the needs of sample separation and multiple washing steps. [ABSTRACT FROM AUTHOR]

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 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. [ABSTRACT FROM AUTHOR]

We describe here an ultrasensitive electrochemical detection of metronidazole (MNZ) by using a freestanding Au-Ag alloy microrod (AMR) as working electrode. Nanoporous Au-Ag AMR (NPAMR) was facilely prepared by dealloying of smooth AMR and further modified with electropolymerized molecularly imprinted polymer (MIP), which affords simultaneous identification and quantification of the target molecules by cyclic voltammetry (CV) with Fe(CN) 6 3−/4− as probe to indicate the current intensity. The MIP-decorated NPAMR showed a remarkably low detection limit of 2.7 × 10 −14 M (S/N = 3) and a wide determination range from 8.0 × 10 −14 to 1.0 × 10 −6 M for MNZ. The developed sensor has been successfully applied in detection of MNZ in real samples (fish tissues and drug tablet), and admirable specificity and anti-interference capability were achieved. This protocol offers great promise for cost-effective and precisely quantitative analysis of trace biological and chemical substances without assistance of any extra working electrode. [ABSTRACT FROM AUTHOR]