Gold-silver Bimetallic Nanoparticles Research Articles

Unraveling Structural Information of Turkevich Synthesized Plasmonic Gold-Silver Bimetallic Nanoparticles.

For the synthesis of gold-silver bimetallic nanoparticles, the Turkevich method has been the state-of-the-art method for several decades. It is presumed that this procedure results in a homogeneous alloy, although this has been debatable for many years. In this work, it is shown that neither a full alloy, nor a perfect core-shell particle is formed but rather a core-shell-like particle with altering metal composition along the radial direction. In-depth wet-chemical experiments are performed in combination with advanced transmission electron microscopy, including energy-dispersive X-ray tomography, and finite element method modeling to support the observations. From the electron tomography results, the core-shell structure can be clearly visualized and the spatial distribution of gold and silver atoms can be quantified. Theoretical simulations are performed to demonstrate that even though UV-vis spectra show only one plasmon band, this still originates from core-shell type structures. The simulations also indicate that the core-shell morphology does not so much affect the location of the plasmon band, but mainly results in significant band broadening. Wet-chemistry experiments provide the evidence that the synthesis pathway starts with gold enriched alloy cores, and later on in the synthesis mainly silver is incorporated to end up with a silver enriched alloy shell.

An Immunosensor Based on Au-Ag Bimetallic NPs Patterned on a Thermal Resistant Flexible Polymer Substrate for In-Vitro Protein Detection.

Nanosensors based on flexible polymers have emerged as powerful tools for next generation smart devices in the recent years. Here, we report a facile protocol to fabricate an immunosensor supported by a thermally resistant flexible polymer substrate (polyarylene ether nitrile, PEN). The immunosensor is a localized surface plasmon resonance (LSPR) optical sensor for in-vitro protein detection based on anti-body coated gold-silver bimetallic nanoparticles (Au-Ag NPs) immobilized on a PEN substrate. Plasmonic spectroscopy and morphological characterization show that the Au-Ag NPs essentially exhibit a more uniform size distribution and higher quality factors than those from single-component Au NPs. Furthermore, it should be noted that the robust PEN substrate in this nanosensor acts a flexible substrate to support Au-Ag NPs and immobilize the nanoparticles via quick thermal annealing at 290 °C. Thanks to these merits, a prostate-specific antigen (PSA) concentration as low as 1 ng/mL can be specifically discriminated via the prepared PEN/Au-Au NPs, which confirms that the protocol reported in this work can be readily adapted for the construction of various flexible immunosensors for different applications.

Gold-silver bimetallic nanoparticles with a Raman labeling chemical assembled on silica nanoparticles as an internal-standard-containing nanoprobe

Surface-enhanced Raman scattering (SERS) has a great potential as a sensitive probe for analytical detection, but the low level of reproducibility remains a challenge for quantitative detection. To enhance the reproducibility, an internal standard that is incorporated between the core and shell structure of metal nanoparticles (NPs) can be employed. However, the unstable sol form of “core-shell” substrates has been unsatisfactory, causing rapid agglomeration. Herein, we prepared a SERS-active core-Raman labeling chemical (RLC)-shell material based on Au-Ag NPs assembled on silica NPs (SiO2@Au@RLC@Ag NPs) as internal-standard-containing NPs. When 4-mercaptobenzoic acid (4-MBA) was used as a model RLC with a silica template, the Raman intensity of SiO2@Au@4-MBA@Ag was ∼8-fold higher than that without a silica template (Au@4-MBA@Ag NPs). Concentrations of 4-MBA in the range of 1 × 10−6 to 1 × 10−2 M incorporated between the SiO2@Au core and the Ag shell did not significantly affect the Ag shell coating. Nevertheless, the Raman intensity increased linearly and was proportional to the logarithm of the 4-MBA concentration. When SiO2@Au@4-MBA@Ag was utilized as internal-standard-containing NPs, the dynamic linear range of thiram detection was 5–50 μM with a limit of detection of 1.2 μM. These results show that our material can be used for the broad dynamic detection of (bio)-chemical traces with high sensitivity.

Bimetallic Gold-Silver Nanoparticles Supported on Zeolitic Imidazolate Framework-8 as Highly Active Heterogenous Catalysts for Selective Oxidation of Benzyl Alcohol into Benzaldehyde.

The metal-organic zeolite imidazolate framework-8 (ZIF-8) supported gold-silver bimetallic catalysts with a core-shell structure (Au@Ag/ZIF-8 and Ag@Au/ZIF-8) and cluster structure (AuAg/ZIF-8) were successfully prepared by the deposition-redispersion method. Energy dispersive X-ray spectroscopy (EDS) elemental mapping images displayed that in the Au@Ag/ZIF-8 catalyst, Ag atoms were deposited on an exposed Au surface, and core-shell structured Au@Ag particles with highly dispersed Ag as the shell were formed. Additionally, the XPS investigation at gold 4f levels and silver 3d levels indicated that the Au and Ag particles of Au@Ag/ZIF-8, Ag@Au/ZIF-8, and AuAg/ZIF-8 were in a zero valence state. Among the resultant catalysts obtained in this study, Ag@Au/ZIF-8 catalysts showed the highest catalytic activity for the selective oxidation of benzyl alcohol, followed by AuAg/ZIF-8 and Au@Ag/ZIF-8. The turnover frequency (TOF) values were in the order of Ag@Au/ZIF-8 (28.2 h−1) > AuAg/ZIF-8 (25.0 h−1) > Au@Ag/ZIF-8 (20.0 h−1) at 130 °C within 1 h under 8 bar O2 when using THF as solvent. The catalysts of Au@Ag/ZIF-8 and Ag@Au/ZIF-8 with core–shell structures have higher benzaldehyde selectivities (53.0% and 53.3%) than the AuAg/ZIF-8 catalyst (35.2%) in the selective oxidation of benzyl alcohol into benzaldehyde. The effect of the solvent, reaction temperature, reaction time, and reaction pressure on benzyl alcohol conversion and benzaldehyde selectivity in benzyl alcohol selective oxidation over Au@Ag/ZIF-8, Ag@Au/ZIF-8, and AuAg/ZIF-8 were also investigated. All of the catalysts showed excellent performance at 130 °C under 8 bar O2 within 1 h when using THF as the solvent in the selective oxidation of benzyl alcohol to benzaldehyde. Moreover, the catalysts can be easily recycled and used repetitively at least four times.

Synthesis of Bimetallic Gold-Silver (Au-Ag) Nanoparticles for the Catalytic Reduction of 4-Nitrophenol to 4-Aminophenol

Bimetallic gold-silver nanoparticles as unique catalysts were prepared using seed colloidal techniques. The catalytic capabilities of the nanoparticles were ascertained in the reduction of 4-nitrophenol to 4-aminophenol in the presence of sodium borohydride. Our results clearly showed that the rate of 4-NP reduction to 4-AP increased with a corresponding decrease in the diameter of the bimetallic NPs. The Au-Ag nanoparticles prepared with 5.0 mL Au seed volume indicated higher reduction activity, which was approximately 1.2 times higher than that of 2.0 mL Au seed volume in the reductive conversion of 4-NP to 4-AP. However, the monometallic NPs showed relatively less catalytic activity in the reductive conversion of 4-NP to 4-AP compared to bimetallic Au-Ag nanoparticles. Our studies also reinforced the improved catalytic properties of the bimetallic Au-Ag nanoparticles structure with a direct impact of the size or diameter and relative composition of the bimetallic catalytic nanoparticles.

Formation of bimetallic gold-silver nanoparticles in glass by UV laser irradiation

Experimental technique for preparing of space arranged arrays of bimetallic AuAg nanoparticles in the near-surface region of glass, exhibiting surface plasmon resonance (SPR) characteristics varying in the wider ranges comparing to monometallic Au, Ag particles or corresponding thin films, is presented together with the structural characterization of the obtained particles. The suggested technique is based on the UV laser irradiation (λ = 193 nm) of the glass surface preliminary doped with silver ions and then sputter coated by a thin gold layer. Optical extinction spectra of the prepared AuAg/glass samples demonstrated strong dependence of SPR upon the number of laser pulses applied. The relationship “SPR characteristics – particles structure and composition – synthesis conditions” was studied using transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray fluorescence (XRF) method and X-ray absorption fine structure (XAFS) spectroscopy. The latter provided the structural information on AuAg bonds, which directly evidenced on the formation of bimetallic AuAg nanoparticles in AuAg/glass samples. The XAFS derived values of structural parameters of AuAu and AuAg bonds allowed to visualize the distribution of gold and silver over the volume of representative AuAg nanoparticle and to suggest the most plausible cluster models of the architecture of such particle for the prepared AuAg/glass samples. It was revealed that the core-shell architecture of Au@Ag particles (Au-core, Ag-shell) is the most plausible in AuAg/glass samples prepared by the low number of laser pulses, while the structure of disordered solid solution is suitable for AuAg particles in samples prepared by ∼ 50 and more pulses. Calculations of contributions into experimental optical extinction spectra of AuAg/glass samples from particles with the revealed composition, size and architecture were performed to prove that the proposed structural models of nanoparticles are not in contradiction with the observed optical properties of the samples.

Antioxidant activity of phytosynthesized biomatrix-loaded noble metallic nanoparticles

Abstract Biofabrication of noble monometallic platinum nanoparticles (Pt-NPs) and bimetallic gold–silver nanoparticles (AuAg-NPs) using aqueous extract of Delonix regia is presented here. Antioxidant activity of biomatrix-loaded metallic nanoparticles is estimated for scavenging of two model radicals i.e., 2,2′-Azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt and 1,1′-Diphenyl-2-picrylhydrazyl. Broad spectral continuum spanning from visible to ultra-violet region (Pt-NPs: 30 min) and broad high intensity absorption peak around at 500 nm (AuAg-NPs: 10 min) in two different UV–Visible spectra confirmed the biofabrication. Nanoparticles fabricated with distorted spherical shape and crystalline face-centred-cubic geometry. Strong signal around at 2.10 keV (pure-phase platinum) and typical X-ray peaks observed at 2.20 and 3 keV suggested, co-existence and alloying interaction of Au and Ag in AuAg-NPs. ζ potential (− 15.2 mV: Pt-NPs and − 13.9 mV: AuAg-NPs) values suggested surface adsorption of polyphenolic compounds to provide stability. Nanoparticles exhibited pronounced antioxidant activity against free radicals through their electron/hydrogen transfer ability.

Biogenic Synthesized Ag/Au Nanoparticles: Production, Characterization, and Applications

Background: Bimetallic silver-gold nanoparticles (Ag/Au NPs) with different structures have recently gained scientific attention due to their new and superior properties in comparison with metallic NPs made from a single metal. Ag/Au NPs (alloy or core-shell structures) have been applied to several biomedical, technological, and environmental applications. The potential applications of Ag/Au NPs are widespread yet poorly investigated in comparison with monometallic NPs. Besides traditional chemical and physical routes to synthesize bimetallic Ag/Au NPs, biogenic protocols are considered cost-effective, simple, and environmentally friendly. Despite their simplicity, biogenic routes to synthesize Ag/Au NPs are less explored than traditional synthetic protocols. Methods: In this context, we present a review and discuss recent progress in the preparation of bimetallic Ag/Au NPs with different morphologies, structures, and size distributions using biogenic synthetic protocols. Results: Biogenic synthesis using plant extracts, algae, bacteria, fungi, and other biological agents are presented and discussed. The characterization and potential applications of biogenically synthesized Ag/Au NPs in the different areas of medicine and biological applications, such as antibacterial, anticandidal, anticancer, antidiabetes, and as sensors for clinical diagnosis are presented and discussed. Conclusion: Finally, challenges and drawbacks in the biological routes for the preparation of Ag/Au NPs for industrial applications are also discussed.

Highly sensitive amperometric biosensor for determination of NADH and ethanol based on Au-Ag nanoparticles/poly(L-Cysteine)/reduced graphene oxide nanocomposite

This work presents the fabrication of a novel nicotinamide adenine dinucleotide (NADH) sensor using gold-silver bimetallic nanoparticles (Au-AgNPs), poly(L-Cysteine) (P(L-Cys)) and electrochemically reduced graphene oxide (ERGO) modified glassy carbon electrode (GCE/Au-AgNPs/P(L-Cys)-ERGO). The composite electrode exhibited an excellent electrocatalytic response towards NADH at a low oxidation potential (+ 0.35V) and minimization of surface contamination due to the synergistic effects of the Au-AgNPs, polymer and ERGO. Under optimum conditions, modified sensors allowed the detection of NADH with a wide linear range from 0.083µM to 1.05mM with a low detection limit of 9.0nM (S/N = 3). Moreover, this modified electrode was also used as a sensitive ethanol biosensor, which was prepared with alcohol dehydrogenase (ADH) via glutaraldehyde, bovin serum albumin and nafion (Naf). There was a linear response for ethanol in the concentration range from 0.017 to 1.845mM with a low detection limit of 5.0µM (S/N = 3). The GCE/Au-AgNPs/P(L-Cys)-ERGO/ADH/Naf electrode can be successfully used for the determination of ethanol in different commercial beverages.

Polypeptide-Facilitated Formation of Bimetallic Plasmonic Nanoparticles in Presence of Ionizing Radiation

Ionizing radiation, which includes X-rays and gamma rays, is used in a variety of different applications, including in human health. However, high levels of exposure can result in significant morbidity and mortality in humans. Molecular and nanoscale systems that can detect different levels of ionizing radiation can ultimately lead to effective sensing platforms for a variety of applications. In the current work, we describe the use of polypeptide-templated formation of bimetallic metal nanoparticles with potential applications as a colorimetric reporter of elevated levels of ionizing radiation typically used in blood irradiation. Cysteine-containing elastin-like polypeptides were employed together with reducing agents in order to engender radiation-facilitated formation of bimetallic gold–silver bimetallic nanoparticles from a mixture of their respective metal salts. This formation of colored nanoparticle dispersions from colorless metal salt solutions acted as a visual reporter of ionizing radiation in the dose range of 25–100 Gy. Nanoparticles were characterized using UV–visible spectroscopy, transmission electron microscopy, elemental analyses and dynamic light scattering. Our results indicate that polypeptide-bimetallic nanoparticle systems may be attractive reporters of elevated levels of ionizing radiation.

Synthesis and characterization of core-shell bimetallic nanoparticles for synergistic antimicrobial effect studies in combination with doxycycline on burn specific pathogens

Nano-medicine is a breakthrough discovery in the healthcare sector. Doxycycline is a new generation antibiotic which is proved to be a boon in the treatment of patients with complicated skin infections. We have tried to explore the benefits of synthesized bimetallic silver-gold nanoparticles in combination with new generation antibiotic for burn infections. The bimetallic nanoparticles synthesized by core-shell method were characterized using scanning electron microscopy equipped with an energy dispersive spectrometer, transmission electron microscopy, X-ray diffraction and UV–Vis spectroscopy. The calculated average particle sizes of the Ag-Au NPs were found to be 27.5nm. The Ag-Au core-shell BNPs show a characteristic Plasmon peak at 525nm which is broad and red shifted. The synergistic antimicrobial activity of doxycycline conjugated bimetallic nanoparticles was investigated against Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus and Micrococcus luteus. This combined therapeutic agent showed greater bactericidal activity. Synergy of antibiotic with bimetallic nanoparticles is quite promising for significant application in burn healing therapy. The mechanism of the antibacterial activity was studied through the formation of reactive oxygen species (ROS) that was later suppressed with antioxidant to establish correlation with the Ag-Au NPs antimicrobial activity. Ag-Au NPs showed effective antiproliferative activity toward A549 human lung cancer (CCL-185) and MCF-7 human breast cancer (HTB-22) cell lines.

Potent antimicrobial and antibiofilm activities of bacteriogenically synthesized gold-silver nanoparticles against pathogenic bacteria and their physiochemical characterizations.

The objective of this study was to develop a bimetallic nanoparticle with enhanced antibacterial activity that would improve the therapeutic efficacy against bacterial biofilms. Bimetallic gold-silver nanoparticles were bacteriogenically synthesized using γ-proteobacterium, Shewanella oneidensis MR-1. The antibacterial activities of gold-silver nanoparticles were assessed on the planktonic and biofilm phases of individual and mixed multi-cultures of pathogenic Gram negative (Escherichia coli and Pseudomonas aeruginosa) and Gram positive bacteria (Enterococcus faecalis and Staphylococcus aureus), respectively. The minimum inhibitory concentration of gold-silver nanoparticles was 30-50 µM than that of other nanoparticles (>100 µM) for the tested bacteria. Interestingly, gold-silver nanoparticles were more effective in inhibiting bacterial biofilm formation at 10 µM concentration. Both scanning and transmission electron microscopy results further accounted the impact of gold-silver nanoparticles on biocompatibility and bactericidal effect that the small size and bio-organic materials covering on gold-silver nanoparticles improves the internalization and thus caused bacterial inactivation. Thus, bacteriogenically synthesized gold-silver nanoparticles appear to be a promising nanoantibiotic for overcoming the bacterial resistance in the established bacterial biofilms.

AuCu, AgCu and AuAg Bimetallic Nanoparticles: Synthesis, Characterization and Water Remediation

ABSTRACTSelf-assembling systems of amphiphilic molecules display structures similar to those of biomineralization natural systems. This allows to somehow mimic nature to synthesize nanomaterials with low polidispersity and with diverse morphologies. In this work we describe the synthesis and characterization of gold-copper, silver-copper, and gold-silver bimetallic nanoparticles by chemical reduction in self-assembling systems of two surfactants. The nanoparticles were characterized by Transmission Electron Microscopy and UV-Vis spectroscopy. We have prepared a composite material using mesoporous silica as support of the AuAg bimetallic nanoparticles. The system was used in photocatalysis experiments for water remediation applications. Our results show that the AuAg/SBA15 composite material degrades methyl orange in water from 17 ppm to 4 ppm in 30 minutes.

Eco-friendly synthesis of gelatin-capped bimetallic Au-Ag nanoparticles for chemiluminescence detection of anticancer raloxifene hydrochloride.

This study described the utility of green analytical chemistry in the synthesis of gelatin-capped silver, gold and bimetallic gold-silver nanoparticles (NPs). The preparation of nanoparticles was based on the reaction of silver nitrate or chlorauric acid with a 1.0wt% aqueous gelatin solution at 50°C. The gelatin-capped silver, gold and bimetallic NPs were characterized using transmission electron microscopy, UV-vis, X-ray diffraction and Fourier transform infrared spectroscopy, and were used to enhance a sensitive sequential injection chemiluminescence luminol-potassium ferricyanide system for determination of the anticancer drug raloxifene hydrochloride. The developed method is eco-friendly and sensitive for chemiluminescence detection of the selected drug in its bulk powder, pharmaceutical injections and biosamples. After optimizing the conditions, a linear relationship in the range of 1.0×10(-9) to 1.0×10(-1) mol/L was obtained with a limit of detection of 5.0×10(-10) mol/L and a limit of quantification of 1.0×10(-9) mol/L. Statistical treatment and method validation were performed based on ICH guidelines. Copyright © 2016 John Wiley & Sons, Ltd.

Tuning the composition of gold–silver bimetallic nanoparticles for the electrochemical reduction of hydrogen peroxide and nitrobenzene

Gold@silver core–shell nanoparticles were synthesized by galvanic displacement reaction and modified on glassy carbon electrode for the reduction of hydrogen peroxide and nitrobenzene.

Paper-Based Analytical Devices Relying on Visible-Light-Enhanced Glucose/Air Biofuel Cells.

A strategy that combines visible-light-enhanced biofuel cells (BFCs) and electrochemical immunosensor into paper-based analytical devices was proposed for sensitive detection of the carbohydrate antigen 15-3 (CA15-3). The gold nanoparticle modified paper electrode with large surface area and good conductibility was applied as an effective matrix for primary antibodies. The glucose dehydrogenase (GDH) modified gold-silver bimetallic nanoparticles were used as bioanodic biocatalyst and signal magnification label. Poly(terthiophene) (pTTh), a photoresponsive conducting polymer, served as catalyst in cathode for the reduction of oxygen upon illumination by visible light. In the bioanode, electrons were generated through the oxidation of glucose catalyzed by GDH. The amount of electrons is determined by the amount of GDH, which finally depended on the amount of CA15-3. In the cathode, electrons from the bioanode could combine with the generated holes in the HOMO energy level of cathode catalysts pTTh. Meanwhile, the high energy level photoexcited electrons were generated in the LUMO energy level and involved in the oxygen reduction reaction, finally resulting in an increasing current and a decreasing overpotential. According to the current signal, simple and efficient detection of CA15-3 was achieved.

Biogenic nanoparticles bearing antibacterial activity and their synergistic effect with broad spectrum antibiotics: Emerging strategy to combat drug resistant pathogens

The present study emphasizes on synthesis of bimetallic silver–gold nanoparticles from cell free supernatant of Pseudomonas veronii strain AS41G inhabiting Annona squamosa L. The synthesized nanoparticles were characterized using hyphenated techniques with UV–Visible spectra ascertained absorbance peak between 400 and 800nm. Possible interaction of biomolecules in mediating and stabilization of nanoparticles was depicted with Fourier transform infrared spectroscopy (FTIR). X-ray diffraction (XRD) displayed Bragg’s peak conferring the 100, 111, 200, and 220 facets of the face centered cubic symmetry of nanoparticles suggesting that these nanoparticles were crystalline in nature. Size and shape of the nanoparticles were determined using Transmission electron microscopy (TEM) microgram with size ranging from 5 to 50nm forming myriad shapes. Antibacterial activity of nanoparticles against significant human pathogens was conferred with well diffusion assay and its synergistic effect with standard antibiotics revealed 87.5% fold increased activity with antibiotic “bacitracin” against bacitracin resistant strains Bacillus subtilis, Escherichia coli and Klebsiella pneumoniae followed by kanamycin with 18.5%, gentamicin with 11.15%, streptomycin with 10%, erythromycin with 9.7% and chloramphenicol with 9.4%. Thus the study concludes with biogenic and ecofriendly route for synthesizing nanoparticles with antibacterial activity against drug resistant pathogens and attributes growing interest on endophytes as an emerging source for synthesis of nanoparticles.

Investigation of bimetallic nanoparticles with broad plasmon response

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

Correlating the Atomic Structure of Bimetallic Silver–Gold Nanoparticles to Their Antibacterial and Cytotoxic Activities

Silver nanoparticles (AgNPs) have gained much attention in biomedical research because of their antibacterial properties. However, they have also exhibited cytotoxicity toward certain mammalian cells. In order to improve therapeutic efficacy, the incorporation of gold (Au) and Ag into bimetallic Ag–Au NPs is a promising strategy, as it has the potential to increase biocompatibility and maintain antibacterial activity. Toward this end, we prepared a series of bimetallic Ag–Au NPs and studied them with X-ray absorption spectroscopy (XAS) in order to elucidate the correlation of atomic structure to their bioactivities. The addition of Au was found to drastically change the atomic structure of the Ag NPs; namely, the Ag core of the NPs was gradually replaced with Au, while Ag was found mostly on the surface. Next, NP antibacterial activity toward S. aureus and cytotoxicity toward NIH-3T3 fibroblast cells were assessed. It was found that the antibacterial activity of the bimetallic NPs was lower than pure Ag N...

Nanostructure of wet-chemically prepared, polymer-stabilized silver-gold nanoalloys (6 nm) over the entire composition range.

Bimetallic silver-gold nanoparticles were prepared by co-reduction using citrate and tannic acid in aqueous solution and colloidally stabilized with poly(N-vinylpyrrolidone) (PVP). The full composition range of silver : gold from 0 : 100 to 100 : 0 (n : n) was prepared with steps of 10 mol%. The nanoparticles were spherical, monodispersed, and had a diameter of ∼6 nm, except for Ag : Au 90 : 10 nanoparticles and pure Ag nanoparticles which were slightly larger. The size of the nanoalloys was determined by differential centrifugal sedimentation (DCS) and transmission electron microscopy (TEM). By means of X-ray powder diffraction (XRD) together with Rietveld refinement, precise lattice parameters, crystallite size and microstrain were determined. Scanning transmission electron microscopy (STEM) combined with energy-dispersive X-ray spectroscopy (EDX) and electron energy loss spectroscopy (EELS) showed that the particles consisted of a gold-rich core and a silver-rich shell. XRD and DCS indicated that the nanoparticles were not twinned, except for pure Ag and Ag : Au 90 : 10, although different domains were visible in the TEM. A remarkable negative deviation from Vegard's linear rule of alloy mixtures was observed (isotropic contraction of the cubic unit cell with a minimum at a 50 : 50 composition). This effect was also found for Ag:Au bulk alloys, but it was much more pronounced for the nanoalloys. Notably, it was much less pronounced for pure silver and gold nanoparticles. The microstrain was increased along with the contraction of the unit cell with a broad maximum at a 50 : 50 composition. The synthesis is based on aqueous solvents and can be easily scaled up to a yield of several mg of a well dispersed nanoalloy with application potential due to its tuneable antibacterial action (silver) and its optical properties for bioimaging.