Ag Shell Research Articles

A SERS/colorimetric biosensor based on AuNSs@Ag core-shell Prussian blue nanozyme for non-interference and rapid detection of Staphylococcus aureus in milk.

AAuNSs@PB@Ag-Apt surface-enhanced Raman scattering (SERS) probehas been developedby embedding Prussian blue (PB) between Au core and Ag shell. The PB SERS probe illustrates strong SERS activity in the Raman silent region of 2070 cm-1, and has a zero background signal, ensuring high sensitivity for the detection ofStaphylococcus aureus(S. aureus).Moreover, the assemble SERS probe exhibits the catalytic function of peroxidase (POD), enabling the catalysis of 3,3',5,5'-tetramethylbenzidine (TMB) for colorimetric detection. Additionally, we prepared lectin-functionalized magnetic nanoparticles (F-MNPs-ConA) that demonstrate superior adsorption capabilities towards S. aureus, achieving an impressive adsorption valueof up to 98.62%. The F-MNPs-ConA/S. aureus/AuNSs@PB@Ag-Apt sandwich structure constructed by the above SERS probe and magnetic nanoparticles achieves highly sensitive detection of S. aureus. The detection range is 1 × 100 ~ 1 × 108 CFU·mL-1, and the detection limit (LOD) is 1 CFU·mL-1. Notably, this method can be integrated into smartphones, facilitating rapid and on-site detection of S. aureus. Compared withsimilar biosensors, this biosensor offers distinct advantages, including a wide detection range and a low detection limit. The reliability of the biosensor was confirmed by its application in milk, where the recovery ranged from 93.66 to 120.8%. The dual-mode SERS/colorimetric detection, non-interfering nature, magnetic enrichment, and reusability of the biosensor make it a promising tool for point-of-care testing (POCT).

Ultrasensitive sulphide detecting by using Au (core)-Ag (shell) triangular nanoprisms

Hydrogen sulfide (H2S), the third endogenous gaseous molecule, plays a crucial role in biological signaling and metabolic processes. It has garnered significant attention from researchers in the field of biochemistry. The highly sensitive detection of H2S is essential for elucidating its functions and has long been a key objective in biochemical sensing. In this study, we present an ultrasensitive method for sulfide detection utilizing gold (core)-silver (shell) triangular nanoprisms (Au@Ag TNPs). This strategy is predicated on the preferential formation of Ag2S at the sharp corners of Au@Ag TNPs, which is manifested as a sensitive spectral shift observed in the nanoprobes. In comparison to the detection limit for sulfide using Au@Ag nanorods, as reported in Nat. Commun. 4, 1708 (2013)10.1038/ncomms2722, this detection limit can be enhanced by three orders of magnitude when employing Au@Ag TNPs. Leveraging the single-particle scattering spectrum of individual Au@Ag TNPs, we have successfully reduced the detection limit for sulfide to 1 fM. This represents the lowest reported value for sulfide detection to date. This study presents a highly effective plasmonic nanoprobe for ultrasensitive sulfide detection, which is poised to play a significant role in biochemistry and environmental sciences.

Synthesis of Chiral Au-Ag Core-Shell Nanoparticles and Their Localized Surface Plasmon Resonance Properties

Noble metal nanoparticles (NPs) such as silver (Ag), and gold (Au) exhibit localized surface plasmon resonance (LSPR) peaks in the visible light region, and their optical properties can be tuned by their size and shape. Advances in colloid chemistry enable the introduction of structural chirality to these plasmonic NPs. LSPRs of chiral metal NPs are responsive to circularly polarized light (CPL), giving them chiroptical properties. For example, Au nanoparticles prepared with L- or D-cysteines as a ligand showed almost the same shape of extinction spectra, but their CD spectra showed opposite peaks in the LSPR wavelength region, depending on the handedness of ligands.[1] Metal nanoparticles having chiral structures are expected to be applied to high-sensitivity chiral sensing. While Au nanoparticles have been extensively explored due to their high chemical stability, chiral Ag nanostructures have not been investigated in spite of the potential for a stronger LSPR-induced electric field. In this study, we report the development of a novel colloidal method to synthesize chiral Au-Ag core-shell nanoparticles via electrochemical deposition of Ag layer onto the surface of pre-synthesized chiral Au nanoparticles.Chiral Au NPs were prepared according to a previous report using L-cysteine as the ligand.[1] Thus-prepared NPs were loaded on a glassy carbon (GC) electrode. A Cu monolayer was deposited on Au NPs by the underpotential deposition (UPD) in an aqueous solution containing 1.0 mmol dm-3 CuSO4. The Cu UPD layer was replaced with Ag through galvanic replacement by immersing the electrode with the Cu-UPD Au NPs in a 10 mmol dm-3 AgNO3 aqueous solution. The amount of Ag deposition on individual Au NPs was controlled by repeating the procedures of Cu UPD and Ag replacement.Cyclic voltammograms were measured on GC electrodes loaded with chiral Au NPs in a CuSO4 solution. With a negative sweep of the electrode potential, a cathodic current peak originating from the Cu UPD was observed at ca. +0.5 V vs. RHE and a current assignable to bulk Cu deposition appeared at the potential more negative than +0.25 V vs. RHE. In contrast, a potential sweep to positive direction generated an anodic current corresponding to the oxidation of the Cu layer. Based on these results, we determined the potential of Cu UPD on chiral Au NPs.The average diameter of chiral Au NPs prepared with L-cysteine was 117 nm, and a twisted surface was confirmed by SEM measurements. Even after three cycles of the above-mentioned Ag deposition procedures, no clear change in the shape of chiral Au NPs was observed. However, the average size of particles increased to 123 nm after these cycles, indicating the deposition of Ag shell layer of ca. 1 nm thickness on Au NPs per cycle. This study successfully demonstrates the preparation of chiral Au-Ag core-shell NPs through electrochemical methods involving Cu UPD on Au NPs and subsequent galvanic replacement with Ag. References (1) K. T. Nam, et al, Nat. Commun, 11, 263 (2020).

Colorimetric detection and automatic quantitative analysis of mercury(II) ions via selective redox reaction sites on silver-coated gold nanorods

Mercury (Hg), particularly Hg(II), poses significant environmental and health risks. Despite its known hazards, Hg2+ is widely used in various industries, thereby underscoring the need for simpler, faster, and more cost-effective methods for managing and monitoring Hg2+ emissions. In this study, we developed a colorimetric detection method for Hg2+ that leveraged the optical changes induced by the redox processes and amalgamation reactions between Au nanorod(NR)@Ag core-shell plasmonic nanoparticles and mercury ions. These nanoparticles were synthesized to exhibit distinct optical shifts by adjusting the Ag shell thickness. This enabled the visual detection of Hg2+ concentrations as low as 100 µM. In addition, changes in the optical spectrum of concentrations as low as 10 nM could be detected with UV–vis spectrometry. Furthermore, to account for individual differences in color perception, an automated analysis protocol was developed using ImageJ software for translating the color changes in smartphone-captured images of the solution into quantitative colorimetric data. This novel approach not only enabled the detection of mercury concentrations as low as 10 nM but also offered a simpler and more economical alternative to traditional methods. Furthermore, it demonstrated potential for implementation as on-site application to monitor mercury concentrations via rapid colorimetric reactions.

Versatile hybrid magnetic core silver-shell (Fe3O4@PEI@Ag) microspheres based SERS substrates for detection of organic dyes pollutant

In recent years, the development of highly sensitive and versatile substrates for Surface-Enhanced Raman Scattering (SERS) has become pivotal in environmental monitoring. This study introduces a hybrid SERS substrate designed to enhance the detection and discrimination of organic dyes in aqueous environments. In this report, we present silver shell magnetic core (Fe3O4@PEI@Ag) microspheres as a versatile SERS substrate for the detection and differentiation of organic dyes, specifically malachite green (MG), crystal violet (CV), Rhodamine 6G (R6G), and Safranin O (S.O), which are often overlooked water pollutants. The core-shell structure of Fe3O4@PEI@Ag microspheres have been synthesized via seed-mediated growth method. The microspheres, integrates a magnetic core of iron oxide (Fe3O4) through a polymeric layer of polyethyleneimine (PEI) with silver shell (Ag), are optimized to act as magnetic separator and show SERS activity. The SEM measurements confirm the spherical shape of grown nano-particles whereas magnetization experiments confirm the presence of magnetic cores as well non-magnetic layers coating in the end products. These microspheres with aluminium (Al) base combination demonstrate high SERS sensitivity with enhancement factor of 1 × 105, 5.6 × 106, 6.4 × 106, and 4.2 × 105 for MG, CV, R6G, and S.O respectively. The detection limits have been found in the range between 10–8–10–10 for all four dyes. A linear relationship between Raman intensity and concentrations of dyes make it suitable for quantitative analysis of unknown concentration. Principal component analysis (PCA), a multivariate analysis has been adopted to discrimination of dyes. These dyes have been effectively detected quantitative in tap water to express substrate's suitability in real-world application. Their dual functionality, as SERS-active substrate and as magnetic separator, enhances their utility in real-world applications such as organic contaminants in aquatic environments.

Optimization and performance assessment of Ag@SiO2 core–shell nanofluids for spectral splitting PV/T system: Theoretical and experiment analysis

Ag@SiO2 nanofluid is widely used in spectral splitting PV/T system. Its core–shell structure has great influence on the optical properties. In this work, we focus on the comprehensive analysis and structure optimization of Ag@SiO2 nanofluid to achieve its optimal spectral performance. DDA method is used to predict the optical properties of Ag@SiO2 nanofluid and an optimization model based on filter efficiency is proposed. The effect of the SiO2 shell thickness and Ag core mass concentration is analyzed. It indicates that the spectral performance of Ag@SiO2 nanofluid can be improved with SiO2 shell thickness of 15–40 nm and Ag core mass concentration of 81–135 mg/L. To achieve the same theoretical merit function of 1.46, the usage of Ag mass can be reduced by 25/33/44/62 % with SiO2 coating of 10/20/40/70 nm. The optimal structure to achieve the highest filter efficiency η of 37.8 % is with a shell thickness of 20 nm and a mass concentration of 113.9 mg/L. An indoor PV/T operation testing is conducted to verify the optimization results. The merit function of Ag-based nanofluids increases from 1.58 to 1.598 and a reduction in Ag usage of 17 % is achieved with a SiO2 coating shell of 17.8 nm. Operation stability is also enhanced with no aggregation observed during the working cycle and 7-day static experiment.

Significant enhancement of bi-directional ultrahigh thermal conductivity in polymer composites fabricated via Polyetherimide@Silver core–shell structured microspheres

Nowadays, the polymer-based composites with excellent thermal-conductive ability and ideal electromagnetic interference shielding performance are in great demand with the advent of developing modern electronic technology. However, most conventional thermal-conductive materials were typically designed to enhance thermal conductivity in just one single direction (through-plane or in-plane direction), which will be inadequate to meet increasing heat-dissipation requirements. Hence, polyetherimide/Silver (PEI/Ag) composites with unique segregated thermal-conductive network were fabricated via hot-pressing the core–shell (PEI@Ag) particles, which was endowed with superior thermal-conductive ability in bi-directions. By this process, the Ag shell was deposited on the surface of various polymer microsphere, and diverse morphology of composite particles would lead to different findings. The results show the PEI@Ag composites with filler content of 18.9 vol% exhibited high in-plane thermal conductivity and through-plane thermal conductivity of 19.9 and 14.0 W/mK, respectively. Particularly, these results achieved obvious improvements of 331 % and 1264 % higher than the composites with filler random distribution, indicating the composite materials obtained outstanding advantage in both horizontal and vertical direction. The research also found that the composites prepared from PEI@Ag core–shell structures possess better properties than those prepared with Ag nanoparticles growing on polymers, indicating the importance of continuous heat-transfer path, and their heat transfer behavior was further demonstrated by finite element analysis. Besides, the composites also exhibited remarkable EMI shielding performance (40.1 dB)). In a word, this study provides viable strategies to enhance the thermal conductivity of composites based on organic solvent-soluble polymer with EMI capability for the development of electronic devices.

Signal-Boosted Electrochemical Lateral Flow Immunoassay for Early Point-of-Care Detection of Liver Cancer Biomarker.

The early diagnosis of cancer in a point-of-need manner is of great significance, yet it remains challenging to achieve the necessary sensitivity and speed. Traditional lateral flow immunoassay (LFIA) methods are limited in accuracy and quantification, restricting their suitability for home-based applications. Thus, we explored a new and user-friendly electrochemical LFIA (e-LFIA) test strip to detect α-fetoprotein (AFP), a diagnostic marker for liver cancer. The specific electrochemical immunoprobe utilized in this e-LFIA test strip is characterized by significant signal boosting, resulted from the loading Ag shell into a gold nanoparticle (AuNP)-coated dendritic mesoporous silica nanoscaffold (DMSN). Leveraging the distinct electrochemical characteristics of Ag anodic stripping and the high volume-to-surface area ratio of DMSNs, the developed DMSNs/AuNPs@Ag-based e-LFIA test strip is capable of detecting AFP at a low concentration of 0.85 ng/mL within a rapid 20 min timespan, both of these values are smaller than those in current clinical testing. Furthermore, we utilized homemade screen-printed electrodes in this sensing prototype and demonstrated the high versatility and reliability of this e-LFIA device. We envision that this DMSNs/AuNPs@Ag-based e-LFIA holds substantial potential for the early diagnosis of liver cancer and household health monitoring.

Shell thickness-dependent Au@Ag nanoparticles for surface-enhanced Raman scattering detection of pollutants

A series of Au@Ag core–shell nanocomposites with varying Ag shell thickness were prepared as potential SERS substrates via chemical reduction method. Rhodamine 6G, crystal violet, and thiram were selected as probes for SERS substrate optimization and sensitivity testing of nanocomposites. According to the results, the Au surface was uniformly coated with a ∼3–12 nm thick Ag layer, exhibiting the even particle size distribution. The above nanocomposites demonstrated an extremely high detection limit for Rhodamine 6G (up to 10−11 M) within a sensitivity range of 10−5 to 10−11 M. At the same time, the detection limits for crystal violet and thiram were 10−10 M and 10−9 M, respectively. Moreover, the SERS performance remained basically unchanged after 30-day storage, indicating good stability and uniformity of Au@Ag substrates. Thus, the proposed Au@Ag nanocomposites have a great application potential for the detection of low-concentration pollutants in the environment along with the prolonged in-use stability.

Poly(N‐Heterocyclic Carbene)‐Capped Alloy and Core‐Shell AuAg Bimetallic Nanoparticles

AbstractN‐Heterocyclic carbene (NHC)‐stabilized metal nanoparticles (NPs) have recently attracted considerable attention. While most efforts in the field have been devoted to the development of NHC‐tethered monometallic NPs and enhancing their stabilities under various conditions, their bimetallic counterparts are rare in the literature. Herein, we demonstrate that the covalent immobilization of Au and Ag atoms on polymerized NHCs is a powerful method to access bimetallic AuAg NPs. In addition, we show that while AuAg alloy NPs are often obtained via this method, the use of bimetallic polymeric substrates with lower Ag content, relative to Au, results in the formation of core–shell NPs with Au core and Ag shell. Application of these nanomaterials for oxygen reduction reaction is demonstrated with all materials exhibiting electrocatalytic activity. This work demonstrates for the first time that while bimetallic poly(NHC‐metal)s are viable substrates to access NHC‐stabilized bimetallic NPs, careful adjustment of metal content in the polymeric substrates can finetune the microstructure of the resulting NPs, i.e. alloy vs. core–shell.

SERS-active core-satellite nanostructures in a membrane filter-integrated microfluidic device for sensitive and continuous detection of trace molecules

We developed a surface-enhanced Raman scattering (SERS)-active plasmonic core-satellite nanostructure and incorporated it into a membrane filter-integrated microfluidic device for continuous monitoring of molecules in solution. The core-satellite nanostructures were fabricated by immobilizing a high number density of gold nanoparticles (AuNPs) on silica beads.to create many nanogaps among the AuNPs. The sizes of the nanogaps were fine-tuned by adding a silver (Ag) shell to optimize the SERS activity. In addition, citrate molecule, the capping agent of the nanoparticles, was displaced by alkali halides. The displacement not only reduced the SERS signals of citrate but also enhanced the adsorption of target molecules. The alkali halide-treated core-satellite nanostructures were accumulated onto a membrane filter integrated into a microfluidic device, serving as a uniform and sensitive SERS substrate. By increasing the volume of the sample solution flowing through the membrane filter, we increased the number of molecules adsorbed to the nanostructures, amplifying the intensities of their characteristic Raman peaks. Our microfluidic SERS device demonstrated continuous SERS detection of malachite green at a concentration as low as 500 fM. In summary, while various core-satellite nanostructures and microfluidic SERS devices have been reported, the integration of the membrane filter-containing microfluidic device with the core-satellite nanostructures facilitated sensitive and continuous molecule detection in our study.

Hyaluronic acid-coated silver nanoparticles releasing Doxorubicin for combinatorial antitumor therapy

Although various nanocarriers have been developed to deliver anticancer drugs to the target tumors, it is still remaining great challenges, including burst release, non-specific targetability and insufficient therapeutic efficacy. Herein, we prepared a multifunctional nanoparticle composed of Ag core and hyaluronic acid shell (Ag NPs@HA) for stimultaneously intracellular delivery of Doxorubicin (DOX) and Ag NPs to improve the anticancer therapeutic efficacy. For our approach, Ag NPs was simply synthesized via the redox reaction between Ag+ ions and catechol group of functional HA, and DOX was subsequently loaded into the HA-coated Ag NPs through the interaction between the remaining catechol groups and DOX (Ag NPs@HA/DOX). The particles exhibited uniform morphology, good biocompatibility to normal cells, and pH-sensitive drug release. Notably, thanks to the specific interaction of HA and CD44 receptor-overexpressing cancer cells, Ag NPs@HA/DOX could dramatically improve the anti-tumor efficacy in vitro as well as in vivo mimicking 3D spheroid model, compared to the free DOX. Moreover, Ag NPs@HA/DOX exhibited superior tumor supression in vivo on a HELA-xenografted mouse model, while minimizing the systemic toxicity of free DOX. From the obtained results, we suggest Ag NPs@HA as potential nanocarrier for targeting delivery of various therapeutic drugs in anticancer therapy.

Dynamical investigation of NinAgm (n + m = 147, 309, 561) nanoalloys with core–shell orderings

ABSTRACT The structures and dynamical properties of core–shell bimetallic Ni-Ag nanoalloys varying with different sizes and compositions have been studied using Monte Carlo (MC) and Molecular Dynamic (MD) simulations. We have considered the compositions in which the size of the core increases while the total number of atoms is fixed. In this sense, two (Ni13Ag134, Ni55Ag92), three (Ni13Ag296, Ni55Ag254, Ni147Ag162) and four (Ni13Ag548, Ni55Ag506, Ni147Ag414 and Ni309Ag252) compositions were considered for 147, 309 and 561 atoms, respectively. Highly symmetric Mackay icosahedral structures with centred symmetric cores appear for these specific sizes and compositions. Also, smaller Ni atoms tend to occupy the core and Ag atoms prefer to segregate to the surface of the nanoalloy due to its lower surface and cohesive energy. Then, the lowest energy structures obtained by Basin Hopping MC simulations were used as initial configurations for melting simulations. The transitions between different chemical ordering patterns with increasing temperature are possible in these systems while they are still in the solid state. Although there are clear differences in the melting process of the compositions with increasing size of the core, for all cases, surface melting occurs indicating that the Ag shell melts before the inner Ni core.

ZIF-8 loaded Ag/ZnO electrospun nanofibers enabling high-performance H2 gas sensing for battery safety early warning

Safety issues triggered by battery thermal runaway have become the most crucial obstacle to the future development of the high-energy-density energy storage systems. As hydrogen (H2) will be inevitably generated along with heat release caused by the side reactions in the early stages of battery thermal runaway, rapid monitoring of trace H2 is considered as an effective measure enabling the battery safety early warning. Herein, to develop high-performance H2 sensing materials to monitor of low-concentration H2 leakage, ZIF-8 loaded Ag/ZnO electrospun nanofibers (ZAZ NFs) were designed by electrospinning and self-sacrificial template methods. Benefiting from all the enrichment and sieving effects of ZIF-8 shell, the catalytic and sensitization effects of Ag and abundant active sites provided by Ag and ZIF-8 loading, the ZAZ sensor enables ppb-level limit of detection toward H2, fast response (9 s), high selectivity and excellent humidity resistance. Furthermore, this ZAZ sensor can also realize the safety early warning (67.79 s before battery bulge) for practical pouch lithium cells, highlighting its great application potential in future advanced battery safety management system.

Reuseable Fe3O4@PEI-DTC-Au@Ag magnetic nanocomposites: A versatile and sensitive SERS substrate for food safety assessment

A novel recyclable SERS substrate with magnetic manipulation capability and surface-enhanced Raman scattering (SERS) effect based on Fe3O4@PEI-DTC-Au@Ag (FPDAA) core-shell nanocomposites has been successfully prepared by engineered hydrothermal deposition and seed deposition techniques. The uniformity and SERS efficacy of these substrates, incorporating various Au@Ag core-shell nanocomposites with differing Ag shell thicknesses, were evaluated using 4-aminothiophenol (4-ATP) molecules. The optimal SERS substrate, Fe3O4@PEI-DTC-Au@Ag-3 (FPDAA-3), exhibited an enhancement factor (EF) of up to 1.121×106. This remarkable performance can be attributed to the synergistic effect between the magnetic plasmon of the Fe3O4 nanoparticles (NPs) core and the surface plasmonic resonance properties of Au@Ag core-shell nanocomposites, which create abundant interparticle hotspots within the FPDAA nanocomposites. Furthermore, the FPDAA-3 nanocomposite was employed as a SERS substrate for rapid thiram detection, achieving a minimum detectable concentration of 1×10−9 M. Notably, the relative standard deviation of SERS measurements from 50 randomly selected points was found to be less than 12.13 %, and the SERS spectra intensity showed minimal variation after 5 cycling tests, underscoring the excellent uniformity and recyclability of the FPDAA-3 substrate. The highly reusable and reliable FPDAA-3 nanocomposites enable direct on-site detection of thiram pesticide residues on fruit skins, thereby offering significant implications for food safety assessment and spectroscopic identification.

Highly luminescent, fast switching electro-optical device based on core-shell bimetallic nanoparticles/ ferroelectric liquid crystal composites.

Owing to the passive nature of liquid crystal (LC) materials, achieving luminous displays using pure LC materials is challenging. In addition, it is difficult to achieve a fast switching time using pristine ferroelectric LC devices without compromising their cell thickness. Herein, we have developed a fast switching and highly luminescent electro-optical device by dispersing a minute concentration of bimetallic nanoparticles (Au@Ag NPs) having a spherical gold core and a silver shell within a ferroelectric liquid crystal (FLC) host matrix, ZLI3654. Au@Ag core-shell NPs having synergic attributes of both counterparts were successfully synthesized by a facile seed-mediated route. The Au core helps to tune the shape of the Ag shell and provides enhanced electron density as well as improved stability against oxidation. Introducing nanoparticles induces little structural modifications to the host FLC, resulting in an improvement in the mesogenic alignment. Interestingly, ∼29-fold enhancement in the photoluminescence (PL) intensity is observed on dispersing 0.25 wt% of Au@Ag NPs into the FLC host matrix. The enhanced electromagnetic field in the FLC-nanocomposite is attributed to the Localized Surface Plasmon Resonance of Au@Ag NPs, which strengthens the photon absorption rates by the FLC molecules, culminating in the massive enrichment of the PL intensity. In addition, the improved localized electric field inside the FLC device led to a noticeable enhancement in the spontaneous polarization, dielectric permittivity, and, most interestingly, ∼53% fastening in the switching time at an optimum concentration (0.25 wt%) of Au@Ag NPs. The improved electro-optical parameters of the Au@Ag NPs/FLC composite have been compared with the performance of both pristine Au NPs/FLC and Ag NPs/FLC composites, respectively, for the comprehensiveness of the study. The present study paves a systematic way to develop FLC-based advanced electro-optical devices with faster switching and higher luminescence properties.

State of the art on plasma-liquid route synthesis monometallic Au, bimetallic Au/Ag core–shell and alloy nanoparticles: Toxicological, сanalytical, antimicrobial activity for environmental control

Nanoparticles (Au monometallic, bimetallic structures Au-Ag alloy and Aucore – Agshell) were synthesized in aqueous solutions with traditional capping agent - sodium citrate, using a one-step (for monometalic and alloy structure) and two–step (for Aucore – Agshell NPs) liquid-phase anode type plasma process. The effects of parameters of synthesis: precursors concentration, the solution plasma process discharge time, molar contents Ag+/Au3+ for alloy NPs, and molar content of Ag+ for Au core NP to the characteristics of the synthesized NPs, including average size (the size distribution, polydispersity index), optical absorption properties ect.) were investigated. The synthesized nanoparticles have the following characteristics: Au NPs with λ=530–540 nm and d = 5–60 nm, the monometalic structure; Ag/Au with the λ=410–530 nm and d = 28–80 nm, bimatalic strucrure of alloy; NPs with significant blue-shift the λ=530→410 nm, depending the shell thickness (the thickness of the deposited Ag shells varied from ∼1–15 nm) and d = 21–35 nm for NPs core(Au)–shell(Ag). TEM images clearly confirm the effectiveness of a one- and two-step plasma-liquid treatment for the synthesis of monometallic Au NPs and the two different structures of the NPs (bimetallic structures Au-Ag alloy and Aucore@– Agshell). The effect of nanoparticle structure on antimicrobial and catalytic properties relative to their respective monometallic counterparts was demonstrated. Among the different investigated structure NPs only for bimetallic core−shell structured AucoreAgshell NPs was found strong synergistic effect for antimicrobial and catalytical activity.

Tunable optical properties of graphene wrapped ZnO@Ag spherical core-shell nanoparticles

In this paper, we studied theoretically and numerically the material’s response to incident electromagnetic wave of graphene wrapped zinc-oxide/silver (g − ZnO@Ag) core–shell spherical nanoparticles embedded in a dielectric host matrix. As the nanoparticles size is ∼30 nm, a size much smaller than the wavelength of light, the quasi-static approximation is utilized to obtain analytical expressions for the electric polarizability and the corresponding extinction cross-section. It is found that the spectra of the extinction cross-section of g − ZnO@Ag nanoparticles exhibit two sets of localized surface resonance peaks in the visible and near infra-red (NIR) spectral regions. The first set of peaks observed below ∼900 nm are due to the coupling of the energy gap of the ZnO core with the local surface plasmon resonances of Ag shell, and the second set of graphene-assisted narrow peaks located in the NIR region (above ∼900 nm) are attributed to the plasmons excited at the Ag/graphene interface. It is found that the intensity of the extinction cross-section as well as the positions of the resonance wavelengths are interesting that the graphene-assisted narrow peaks are strongly dependent on the number of layers (N g ) and the chemical potential (μ) of graphene. It means that the response of ZnO@Ag core–shell nanoparticles to electromagnetic fields are greatly enhanced when it is wrapped with graphene and can also be tuned in the therapeutic NIR spectral region by varying N g and μ. The results may be used for possible application in the medical fields, especially for cancer detection and drug delivery.

Poly(N-Heterocyclic Carbene)-Capped Alloy and Core-Shell AuAg Bimetallic Nanoparticles.

N-Heterocyclic carbene (NHC)-stabilized metal nanoparticles (NPs) have recently attracted considerable attention. While most efforts in the field have been devoted to the development of NHC-tethered monometallic NPs and enhancing their stabilities under various conditions, their bimetallic counterparts are rare in the literature. Herein, we demonstrate that the covalent immobilization of Au and Ag atoms on polymerized NHCs is a powerful method to access bimetallic AuAg NPs. In addition, we show that while AuAg alloy NPs are often obtained via this method, the use of bimetallic polymeric substrates with lower Ag content, relative to Au, results in the formation of core-shell NPs with Au core and Ag shell. Application of these nanomaterials for oxygen reduction reaction is demonstrated with all materials exhibiting electrocatalytic activity. This work demonstrates for the first time that while bimetallic poly(NHC-metal)s are viable substrates to access NHC-stabilized bimetallic NPs, careful adjustment of metal content in the polymeric substrates can finetune the microstructure of the resulting NPs, i.e. alloy vs. core-shell.

Lubrication mechanism of C@Ag core–shell materials as grease additive

The preparation of a low shearing shell on the surface of carbon spheres (CS) is an attractive strategy to improve the lubrication properties of CS. In this study, core–shell structural C@Ag particles were prepared using CS as the hard core and Ag nanoparticles as the soft shell. Then, the additives were mixed with Polyalphaolefin 20 to prepare the C@Ag core–shell-enhanced lithium complex grease (C@Ag-LCG). The physicochemical properties, corrosion resistance, and tribological behaviors of LCGs were investigated. C@Ag-LCG exhibited the best high-temperature resistance and colloidal stability compared with the CS-enhanced lithium complex grease (LCG) and pure LCG. The dropping point and oil separation rate of 0.05 wt% C@Ag-LCG were 255 °C and 2.36 %, respectively. The tribological behavior of greases was tested using a four-ball friction tester, and the main damage mechanism was abrasive wear. The C@Ag additive reduced the average friction coefficient and wear spot diameter by 27.17 % and 26.12 %, respectively. The improved properties were attributed to the synergistic lubrication of hard CS core and soft Ag shell with the rolling, filling, and self-repairing effects, C@Ag deposit films and the self-lubricating oil film, as well as the thickener film and the tribochemical film at the frictional interfaces.