Silver Core Research Articles

Enzymatic Decomposition of Hydrogen Peroxides to Suppress Oxidation of Gold–Silver Core–Shell Nanorods: Colorimetry of Horseradish Peroxidase (HRP) and Catalase

Gold–silver core–shell nanorods were deposited on a glass plate, and the plate was immersed in hydrogen peroxide solution to oxidize the silver shells. When catalase and horseradish peroxidase (HRP) were deposited on the plates, they decomposed the hydrogen peroxide at the surface and suppressed the oxidation of the silver shells. The surface densities of catalase and HRP were 3.1 µg cm−2 and 5 ng cm−2, respectively, comparable to detection limits of conventional enzyme-linked immunosorbent assays. Our protocol has the potential for application in a sensitive and quantitative immunoassay.

Hexa- and Octanuclear Heterometallic Clusters with Copper–, Silver–, or Gold–Molybdenum Bonds and d10–d10 Interactions

A comparative study of the reactivity of the carbonylmetalates {m}− = [MoCp(CO)3]− (Cp = η5-C5H5) and [Mo(η5-C5H4NMe2)(CO)3]− toward d10 complexes of the group 11 metals, [Cu(NCMe)4](BF4), AgBF4 and [N(n-Bu)4][AuBr2], has allowed the characterization of new heterometallic hexa- and octanuclear clusters with the same general formula [M{m}]n (M = Cu, Ag, Au). In these cyclic oligomers, the value of n depends of the coinage metal. Thus, the hexanuclear cluster [Cu3{Mo(η5-C5H4NMe2)(CO)3}3] (17) has a planar metal core, formed by a copper triangle with edge-bridging molybdenum atoms. The octanuclear “star shape” clusters [Ag4{Mo(η5-C5H4NMe2)(CO)3}4] (19) and [Au4{Mo(η5-C5H4NMe2)(CO)3}4] (21) contain a square silver or gold core, respectively, edge-bridged by molybdenum atoms. In these three clusters, the 2-D raft-type structure of their metal core, which is ν2-triangular for Cu3Mo3 and of a square-in-a-square-type for the octanuclear Ag4Mo4 and Au4Mo4 clusters, allows for d10–d10 metallophilic interactions. Th...

Surface plasmon resonance sensor based on photonic crystal fiber filled with core-shell Ag-Au nanocomposite materials

A numerical study of a surface plasmon resonance (SPR) sensor based on photonic crystal fiber (PCF) filled with core-shell Ag-Au nanocomposite materials for measurement of refractive index of the analyte is presented. Considering the design flexibility and improved optical properties of the core-shell bimetallic nanocomposite materials, the proposed sensor is demonstrated to achieve high spectral sensitivity, high detection accuracy, and sensing spectra tuning ability. Meanwhile, the existence of the gold shell can protect the silver core from oxidation, which means high system stability and long lifetime. Based on numerical simulations, the influences of structural parameters of the sensor on sensing properties are discussed. Furthermore, the parameters are optimized by analyzing the simulation results to achieve better performance. It is observed that a high average spectral sensitivity of 5940 nm/RIU with the resolution of 1.68×10−5 RIU in the sensing range of 1.33 to 1.38 can be achieved.

Colorimetric detection of hydrogen peroxide and lactate based on the etching of the carbon based Au-Ag bimetallic nanocomposite synthesized by carbon dots as the reductant and stabilizer

In this report, carbon-based gold core silver shell Au-Ag bimetallic nanocomposite (Au-Ag/C NC) was synthesized using carbon dots (C-dots) as the reductant and stabilizer by a facile green sequential reduction approach. The structure and morphology of the nanocomposite are characterized by ultraviolet–visible spectroscopy (UV–Vis), Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM). The as synthesized Au-Ag/C NC exhibits good optic response toward hydrogen peroxide (H2O2) without adding any other chromogenic agents. The characteristic surface plasmon resonance (SPR) absorbance peak of Au-Ag/C NC declined and red-shifted with the solution color changing from reddish orange to light pink when adding H2O2 owing to the etching effect of H2O2 towards Ag. Thus, a simple colorimetric and UV strategy for sensitive detection of H2O2 is proposed. It provides the wide linear range for detection of H2O2 from 0.8–90 μM and 90–500 μM, and the detection limit was as low as 0.3 μM (S/N = 3). In addition, this colorimetric strategy can also be applied to directly distinguish and detect of lactate by naked eye and UV–Vis. The linear range of colorimetric sensing towards lactate was 0.1–22 μM and 22–220 μM, which was successfully applied in the analysis of lactate in human serum.

Highly Directive Hybrid Yagi-Uda Nanoantenna for Radition Emission Enhancement

In this paper, a novel design of Yagi–Uda nanoantenna is introduced and numerically analyzed using finite integration technique via computer simulation technology software. The proposed nanoantenna consists of five core-shell nanowires with silicon cladding and silver core to achieve high directivity for wireless point to point applications. The proposed design shows a high directivity of 17.21 at a wavelength of 500 nm, which exceeds the spherical dielectric counterparts with directivity of 12. Therefore, an enhancement of 43.41% is achieved, which is mainly useful for spontaneous emission manipulation and photon detection. This enhancement is attributed to the silicon dielectric shell that exhibits magnetic mode with high refractive index, as well as the surface plasmon mode supported by the silver core. Additionally, the proposed cylindrical design has advantages in terms of high homogeneity of the field distribution, which overcomes the inhomogeneity field distribution of the nanosphere-based design.

Modeling of absorption and scattering properties of core -shell nanoparticles for application as nanoantenna in optical domain

The present paper describes the study of core-shell nanoparticles for application as nanoantenna in the optical domain. To obtain the absorption and extinction efficiencies as well as the angular distribution of the far field radiation pattern and the resonance wavelengths for these metal-dielectric, dielectric-metal and metal-metal core-shell nanoparticles in optical domain, we have used Finite Element Method based COMSOL Multiphysics Software and Mie Theory. From the comparative study of the extinction efficiencies of core-shell nanoparticles of different materials, it is found that for silica - gold core - shell nanoparticles, the resonant wavelength is greater than that of the gold - silver, silver-gold and gold-silica core - shell nanoparticles and also the radiation pattern of the silica-gold core-shell nanoparticle is the most suitable one from the point of view of directivity. The dielectric functions of the core and shell material as well as of the embedded matrix are extremely important and plays a very major role to tune the directivity and resonance wavelength. Such highly controllable parameters of the dielectric - metal core - shell nanoparticles make them suitable for efficient coupling of optical radiation into nanoscale structures for a broad range of applications in the field of communications.

Antibacterial silver core spherical nucleic acids

Bacterial drug resistance (DR) has the potential to be one of the most significant medical challenges of the 21st century. Infections involving DR bacterial strains such as methicillin-resistant Staphylococcus aureus (MRSA) or DR Acinetobacter baumannii spread in hospital and community settings and are associated with an increased risk of death. New therapeutic strategies and modalities are needed to treat these DR infections, especially for DR Gram-negative infections. Here, we describe silver-core spherical nucleic acids (Ag-SNAs) as a broad-spectrum antibacterial. Ag-SNAs leverage the broad spectrum antibacterial activity of silver nanoparticles (Ag-NPs), while exhibiting significantly lower (30-fold) minimum inhibitory concentration (MIC) values in comparison to Ag-NPs and reduced toxicity (14-fold) to mammalian cells. Ag-SNAs demonstrate low nanomolar MICs against both DR Gram-negative and DR Gram-positive bacteria in vitro and reduced in vitro toxicity toward human cells vis-à-vis non-derivatized silver nanoparticles. In a topical in vivo wound model involving a multi-DR, clinically-isolated, Gram-negative A. baumannii strain, Ag-SNAs significantly reduced bacterial load as compared to controls (1.51-fold log10 reduction). Our findings open up possibilities for the further development of Ag-SNAs as new antibacterial agents, particularly against challenging DR Gram-negative infections.

Metal-enhanced fluorescent dye-doped silica nanoparticles and magnetic separation: A sensitive platform for one-step fluorescence detection of prostate specific antigen

The world health organization figures show prostate cancer in developed countries has been the second primary cause of cancer mortality following lung cancer for the men. So, early and sensitive diagnosis of cancer is very important before it spreads out to the other organs of the body. It is well-known that prostate-specific antigen (PSA) is the most specific and efficient tumor marker for the diagnosis of prostate cancer. Herein, we successfully fabricated core-shell composite fluorescent nanoparticle Ag@SiO2@SiO2-RuBpy which provide a photoluminescence enhancement of up to ~3-fold when the separation distance between the surface of silver core and the center of the third RuBpy doped silica shell is about 10nm. These core-shell MEF-capable nanoparticles have obvious advantages. The interaction between the doped RuBpy molecules in the outer silica layer and the silver core, greatly improves the excitation efficiency and enhances the fluorescence intensity. Importantly, the presence of silica can reduce the self-quenching of RuBpy, which makes larger amounts of RuBpy incorporated into the silica shell. In addition, the shell protects the RuBpy against collisional quenching and irreversible photodegradation and provides abundant hydroxyl for easy conjugation. After that a highly sensitive, specific and reliable strategy based on metal-enhanced fluorescence and magnetic separation was applied for the detection of PSA in both buffer and serum. The process could be rapidly accomplished, in which the immunomagnetic nanospheres (IMNs) and immunofluorescent nanoparticles (IFNs) were used to capture and identify the target molecules simultaneously. A good linear relationship between the fluorescence intensity and the concentration of PSA (0.1–100ng/mL) with a detection limit 27pg/mL was obtained.

Nanoparticle Dynamics in Room Temperature Ionic Liquids

Nanoparticle dynamics in Room Temperature Ionic Liquids (RTILs) is an underexplored field, despite high interest in RTILs in nanoparticle synthesis, the modification of electrodes and as catalysts. The solvent environment of a RTIL provides a high ionic strength medium in which to understand nanoparticle dynamics and the role of the capping agent in electron transfer to the nanoparticle. Oxidation of silver nanoparticles capped with poly(ethylene) glycol in 1-butyl-3-methylimidazolium tetrafluoroborate (Bmim BF4) is reported for the first time (J. Phys. Chem. C, 2015, 119 (32), 18808-18815). The oxidation of the nanoparticles shows a time dependency, suggesting that the nanoparticles assemble at the electrode surface and time allows the polymer coating to undergo an unwrapping process before the silver core is accessible for electron transfer with the electrode (‘polymer-gated’). The addition of chloride, commonly present as an impurity in RTILs, allows 'nano-impacts', where by the nanoparticle travels to the electrode surface via Brownian motion before undergoing electron transfer as it makes contact with the electrode, to be observed novelly in a RTIL. (J. Phys. Chem. C, 2016, 120 (3), pp 1959–1965). The presence of the chloride allows the nanoparticles to undergo oxidation to silver chloride, which does not require rearrangement of the polymer. Finally, the importance of the capping agent, and its control over the mechanism of oxidation, has been established (Chem. Eur. J, 2016, doi:10.1002/chem.201505117). Examining nanoparticles capped with 2000, 6000, and 10,000 MW poly(ethylene) glycol reveals a shift in the mechanism of silver oxidation (from nano-impact to polymer gated).

Unique Properties of Core Shell Ag@Au Nanoparticles for the Aptasensing of Bacterial Cells

In this article, it is shown that the efficiency of an electrochemical aptasensing device is influenced by the use of different nanoparticles (NPs) such as gold nanoparticles (Au), silver nanoparticles (Ag), hollow gold nanospheres (HGN), hollow silver nanospheres (HSN), silver–gold core shell (Ag@Au), gold–silver core shell (Au@Ag), and silver–gold alloy nanoparticles (Ag/Au). Among these nanomaterials, Ag@Au core shell NPs are advantageous for aptasensing applications because the core improves the physical properties and the shell provides chemical stability and biocompatibility for the immobilization of aptamers. Self-assembly of the NPs on a cysteamine film at the surface of a carbon paste electrode is followed by the immobilization of thiolated aptamers at these nanoframes. The nanostructured (Ag@Au) aptadevice for Escherichia coli as a target shows four times better performance in comparison to the response obtained at an aptamer modified planar gold electrode. A comparison with other (core shell) NPs is performed by cyclic voltammetry and differential pulse voltammetry. Also, the selectivity of the aptasensor is investigated using other kinds of bacteria. The synthesized NPs and the morphology of the modified electrode are characterized by UV-Vis absorption spectroscopy, scanning electron microscopy, energy dispersive X-ray analysis, and electrochemical impedance spectroscopy.

Formation of Large Ag Clusters with Shells of Methane, Ethylene, and Acetylene in He Droplets.

Helium droplets were used to assemble composite metal-molecular clusters. Produced clusters have several hundreds of silver atoms in the core, immersed in a shell consisting of methane, ethylene, or acetylene molecules. The structure of the clusters was studied via infrared spectra of the C-H stretches of the hydrocarbon molecules. The spectra of the clusters containing methane and acetylene show two distinct features due to molecules on the interface with silver core and those in the volume of the neat molecular part of the clusters. The relative intensities of the peaks are in good agreement with the estimates based on the number of the captured particles. Experiments also suggest that selection rules for infrared transitions for molecules adsorbed on metal surfaces are also valid for silver clusters as small as 300 atoms.

A Study of Metal@Graphene Core–Shell Spherical Nano-Geometry to Enhance the SPR Tunability: Influence of Graphene Monolayer Shell Thickness

Graphene, new generation advance material of two dimensional hexagonal lattice having extraordinary optical signatures, is used as coating material to enhance the surface plasmon resonance (SPR) effect of core@shell metal nanospheres. In a core@shell nanosphere, we have chosen metal as a core and graphene monolayer (GML) as a shell. We have analysed optical signature of coated and non-coated nanospheres in terms of extinction efficiency (Q ext) and tunabilty of surface plasmon resonances using electrostatic model, where particle size is much smaller than the wavelength of incident light. We analysed this model over different metals (silver, gold and aluminium) core, coated with different thickness of GML (d = 0.1 to 0.5 nm). These core@shell nanospheres are embedded in refractive index media of air (n em = 1), SiO2 (n em = 1.47) and TiO2 (n em = 2.79). The Q ext has been calculated by varying both the core radii as well as the GML shell thickness. Graphene-coated metal nanosphere exhibits SPRs that have wide range tunability from 300 to 1500 nm. In the presenting work, we also analysed that extinction efficiency for metal@GML is higher in TiO2 than others. The optimum value of GML shell thickness is 0.4 nm for TiO2, the magnitude of extinction efficiency is maximum for the optimum thickness. The tunability of these plasmonic resonances is highly dependent on the core@shell material, thickness of Graphene shell and surrounding environment while non-coated metal nano-spheres do not show appropriate SPR tunability.

Unconventional Fano effect based spectrally selective absorption enhancement in graphene using plasmonic core-shell nanostructures

We present a design of multilayer core-shell nanostructures formed by introducing a dielectric gap shell layer between a silver core and a monolayer graphene shell for spectrally selective absorption enhancement in graphene based on an unconventional Fano effect. We demonstrate that this mechanism enables great flexibility in the choice of parameters of the proposed structures for the achievement of a relatively large and narrow-band absorption enhancement in graphene. Furthermore, we also demonstrate that such a spectrally selective absorption enhancement in graphene is highly tunable and can be optimized by controlling either the core or the shell parameters. These unique absorption properties may have applications in color-selective photodetectors and image sensors.

Catalytic Reduction of 4-Nitrophenol Using Silver Nanoparticles with Adjustable Activity.

We report on the development of ultrasmall core-shell silver nanoparticles synthesized by an upscaled modification of the polyol process. It is foreseen to use these thoroughly characterized particles as reference material to compare the catalytic and biological properties of functionalized silver nanoparticles. Small-angle X-ray scattering (SAXS) analysis reveals a narrow size distribution of the silver cores with a mean radius of Rc = 3.0 nm and a distribution width of 0.6 nm. Dynamic light scattering (DLS) provides a hydrodynamic radius of RH = 10.0 nm and a PDI of 0.09. The particles' surface is covered with poly(acrylic acid) (PAA) forming a shell with a thickness of 7.0 nm, which provides colloidal stability lasting for more than 6 months at ambient conditions. The PAA can be easily exchanged by biomolecules to modify the surface functionality. Replacements of PAA with glutathione (GSH) and bovine serum albumin (BSA) have been performed as examples. We demonstrate that the silver particles effectively catalyze the reduction of 4-nitrophenol to 4-aminophenol with sodium borohydride. With PAA as stabilizer, the catalytic activity of 436 ± 24 L g(-1) s(-1) is the highest reported in the literature for silver nanoparticles. GSH and BSA passivate the surface substantially, resulting in a catalytic activity of 77.6 ± 0.9 and 3.47 ± 0.50 L g(-1) s(-1), respectively.

In Russian

In this paper, we present a theoretical analysis of heating spherical bimetallic nanoparticles with a silver core and a golden shell using laser radiation. The aim of the work is to prove a possibility for applying laser hyperthermia in oncology with use of these nanoparticles. At this, a power and distribution of heat sources in a nanoparticle should be found with subsequent estimation of the temperature in its environs. We investigated a spatial distribution of the field energy in a particle within the electrostatic approximation for homogeneous field acting along the sphere axis. In this case electrostatic energy keeps a stable value in the core but corresponding expression for the shell consists of two terms of the series in expansion on Legendre polynomials. We have constructed a solution of the heat transfer equation for a sphere in a capsule with internal heat sources which intensity is formed by energy distribution of the electrical field. The calculations made show that the temperature necessary for destruction of onco-cells in the nearest environment of the particle can be reached using the laser power that is safe enough for a body system.

Silver-polymer core-shell nanoparticles for ultrastable plasmon-enhanced photocatalysis

Affordable silver-polymer core-shell nanoparticles are prepared using the layer-by-layer (LbL) technique. The metallic silver core is encapsulated with an ultra-thin protective shell that prevents oxidation and clustering without compromising the plasmonic properties. The core-shell nanoparticles retain their plasmonic near field enhancement effect, as studied from finite element numerical simulations. Control over the shell thickness up to the sub-nanometer level is there for key. The particles are used to prepare a plasmonic Ag-TiO2 photocatalyst of which the gas phase photocatalytic activity is monitored over a period of four months. The described system outperforms pristine TiO2 and retains its plasmonic enhancement in contrast to TiO2 modified with bare silver nanoparticles. With this an important step is made toward the development of long-term stable plasmonic (photocatalytic) applications.

Binary plasmonic honeycomb structures: High-resolution EDX mapping and optical properties

Surface coatings with plasmonic nanostructures find applications in a broad range of fields such as sensing, lasing and optoelectronic devices. Structural control is as important as a high resolution structural analysis of these structures for their actual use in relevant applications and the elucidation of structure-property relations. Here we demonstrate the preparation of binary plasmonic honeycomb structures by the sequential double self-assembly of two hexagonally packed monolayers onto the same solid support. Each monolayer consists of noble metal-hydrogel core-shell particles with either gold or silver cores. The honeycomb lattice shows a high degree of order as evidenced by different microscopic techniques and FFT investigation of the positional maps. The plasmonic properties are investigated by UV–vis extinction spectroscopy pointing to plasmon resonance coupling between the different metal cores. High-resolution elemental mapping by EDX is used to unravel the position of the different metal cores with submicron resolution.

Ion Permeation through Silica Coating of Silver Nanoparticles Functionalized with 2-Mercaptoethanesulfonate Anions: SiO2-Encapsulated SERS Probes for Metal Cations

In this work, the first use of thick-silica-protected Ag nanocomposites (Ag-MES@SiO2) in surface enhanced Raman scattering (SERS) detection of metal cations is presented. Several factors which are important for the successful synthesis of silica-encapsulated citrate-free Ag nanoparticles functionalized with sodium 2-mercaptoethanesulfonate (MES) are elucidated. It is shown that negatively charged MES anions adsorbed on Ag surface effectively protect Ag NPs from both aggregation and dissolution in the presence of ammonia. Simultaneously, MES acts as a primer in the modified Stober reaction. Owing to the MES functionalization of the silver core, Ag-MES@SiO2 nanoparticles exhibit intense and stable SERS spectra that are sensitive to metal cations. Based on cation-sensitive SERS spectra of silica-encapsulated MES tags it is proved that 30 nm thick silica shell is permeable for metal cations in short spans of time. Differences between several metal cations in transport through the SiO2 layer are observed, with...

Impact of Silver and Carbon Nanoparticle Exposures on Macrophage Responses to Mycobacterium tuberculosis (M.tb)

Abstract To assess biological risks of nanoparticle (NP) exposures, we examined the effects of silver (Ag) core Ag20-citrate (Ag20) and carbon black (CB) on human host innate immune responses to M.tb, a respiratory pathogen that causes tuberculosis. Human peripheral blood monocyte-derived macrophages (MDMs) were exposed to 1, 10, 25 and 50 μg/mL of Ag20 and CB for 4 and 24 h. At 4 h no significant cytotoxicity was observed with neither of the NPs at none of the concentrations examined relative to unexposed MDMs. At 24 h, viability of the MDMs was reduced by 60–70% and 20% following Ag20 and CB exposure, respectively, at doses ≥25 μg/mL. M.tb-induced host immune responses are mediated by the activation of TLR signalling pathways that culminate in NF-κB activation. Effects of Ag20 and CB (10μg/mL for 4 h, a nontoxic dose) on TLR signalling in M.tb-infected and uninfected MDMs were compared using a human TLR signaling pathway-specific profiler array. Ag20 exposure suppressed the M.tb-induced expression of a subset of NF-κB-mediated target genes (CSF2, CSF3, IFNG, IL1A, IL1B, IL6, IL10, TNFA, NFKB1A). Ag20-mediated suppression of M.tb-induced activation of the TLR-signalling pathway was not due to decreased uptake of M.tb by MDMs or mycobacteriocidal effects of Ag20. Ag20 exposure increased the expression of HSPA1A mRNA that encodes for the stress-induced Hsp72. In contrast, exposure to CB resulted in little effects on M.tb-induced host gene expression indicating that immunosuppressive effects of Ag20 are NP-specific. Since Hsp72 has been shown to suppress NF-κB activation, we propose that Ag20-mediated Hsp72 upregulation contributes to the suppression of M.tb-induced NF-κB activation and host immune responses. Funding NIEHS 5U19 ES019536

Morphology and Optical Properties of Bare and Silica Coated Hybrid Silver Nanoparticles.

Owing to their wide applications in the field of optoelectronics, photonics, catalysis, and medicine; plasmonic metal nanoparticles are attaining considerable interest nowadays. The optical properties of these metal nanoparticles depend upon their size, shape, and surrounding medium. The present work studies the morphology and optical properties of bare silver nanoparticles and silica coated hybrid silver nanoparticles. Aqueous phase mediated synthesis and water-in-oil microemulsion mediated synthesis are two different wet chemical routes employed for nanosynthesis. Direct coating of silica is performed in water-in-oil microemulsion on pre-synthesized silver nanoparticles using tetraethyl orthosilicate as silica precursor. This study shows that using different wet chemical routes the size of the synthesized nanoparticles could be tuned. In addition, using reverse micelles as nanoreactors, the thickness of the silica shell around the core silver nanoparticles could be significantly controlled. Further, the optical properties of silver nanoparticles could be adjusted through the size and the surface coating.