Silver Core Research Articles

Shell-Isolated Nanoparticle-Enhanced Phosphorescence.

The emerging field of plasmonics has promoted applications of optical technology, especially in plasmon-enhanced spectroscopy (PES). However, in plasmon-enhanced fluorescence (PEF), "metal loss" could significantly quench the fluorescence during the process, which dramatically limits its applications in analysis and high-resolution imaging. In this report, silver core silica shell-isolated nanoparticles (Ag@SiO2 NPs or SHINs) with a tunable thickness of shell are used to investigate the interactions between NPs and emitters by constructing coupling and noncoupling modes. The plasmonic coupling mode between Ag@SiO2 NPs and Ag film reveals an exceeding integrating spectral intensity enhancement of 330 and about 124 times that of the radiative emission rate acceleration for shell-isolated nanoparticle enhanced phosphorescence (SHINEP). The experimental findings are supported by theoretical calculations using the finite-element method (FEM). Hence, the SHINEP may provide a novel approach for understanding the interaction of plasmon and phosphorescence, and it holds great potential in surface detection analysis and singlet-oxygen-based clinical therapy.

Low-molecular-weight sulfonated chitosan as template for anticoagulant nanoparticles.

PurposeIn this work, low-molecular-weight sulfoethyl chitosan (SECS) was used as a model template for the generation of silver core-shell nanoparticles with high potential as anticoagulants for medical applications.Materials and methodsSECS were synthesized by two reaction pathways, namely Michael addition and a nucleophilic substitution with sodium vinylsulfonate or sodium 2-bromoethanesulfonate (NaBES). Subsequently, these derivatives were used as reducing and capping agents for silver nanoparticles in a microwave-assisted reaction. The formed silver-chitosan core-shell particles were further surveyed in terms of their anticoagulant action by different coagulation assays focusing on the inhibition of either thrombin or cofactor Xa.ResultsIn-depth characterization revealed a sulfoalkylation of chitosan mainly on its sterically favored O6-position. Moreover, comparably high average degrees of substitution with sulfoethyl groups (DSSE) of up to 1.05 were realized in reactions with NaBES. The harsh reaction conditions led to significant chain degradation and consequently, SECS exhibits masses of <50 kDa. Throughout the following microwave reaction, stable nanoparticles were obtained only from highly substituted products because they provide a sufficient charge density that prevented particles from aggregation. High-resolution transmission electron microscopy images reveal that the silver core (diameter ~8 nm) is surrounded by a 1–2 nm thick SECS layer. These core-shell particles and the SECS itself exhibit an inhibiting activity, especially on cofactor Xa.ConclusionThis interesting model system enabled the investigation of structure–property correlations in the course of nanoparticle formation and anticoagulant activity of SECS and may lead to completely new anticoagulants on the basis of chitosan-capped nanoparticles.

STUDY OF PREPARATION, GROWTH MECHANISM AND SERS PERFORMANCE OF SILVER-CARBON AND GOLD-CARBON NANOCOMPOSITE MATERIALS

Surface-enhanced Raman scattering (SERS) technique is an important and powerful analytical tool, which has attracted much attention for environmental monitoring, chemical analysis and biomedical research. In this paper, we develop a facile method to fabricate the silver-carbon nanocomposites (Ag/CSs) and gold-carbon nanocomposites (Au/CSs). The composites were prepared by one-step hydrothermal reduction method using trioctylamine (TOA) as the soft template and extractant. According to the different amount of TOA added, we prepared a different morphology of the composite material. When the amount of TOA is 1.0 mL, the core-shell composite was obtained. The shape of the silver core shows the hexagon shape and we consider that TOA and glucose selectively adsorb the Ag (111) crystal face resulting in this growth pattern of the silver core. The hydrothermal carbon shell not only effectively avoids the agglomeration of nanoparticles core, but also serves as a protective layer of the SERS active nanostructure during the whole course of the experiment. The detection limit of Ag/CSs for CV molecules up to 10−9 M. The results show that the as-obtained Ag/CSs hold tremendous potential for SERS applications for its long-term stability and superior SERS performance.

Synthesis of Cu@Ag core–shell nanoparticles for characterization of thermal stability and electric resistivity

A two-step synthetic method has been utilized to prepare copper–silver (Cu@Ag) core–shell particles with thin Ag shell coated over a Cu core of initial diameter of 80 ± 5 nm. The formation of core–shell particles is characterized by transmetallation reaction on the surface of the Cu particles, where copper atoms function as the reducer for silver ions. The morphological characterization of Cu@Ag reveals that excess supply of Ag-based reagent produces nanostructures with enhanced core–shell diameter, increased shell thickness, and agglomeration of Ag in the bulk surface, whereas limited supply of Ag species results in nanoparticles with imperfect enveloping of Cu core—making them susceptible to oxidation. Experiments with TGA and DSC verify that thermal stability of core–shell nanoparticles is achieved for the specimen undisturbed by agglomeration and imperfect enveloping effects. Though the electrical resistivity of Cu@Ag nanoparticles increases in general with larger molar proportion of Cu, its increment rate is small for the limit [Cu]:[Ag]=4:1 and then higher beyond it. The sample with [Cu]:[Ag]=4:1, characterized by higher thermal stability, slowest oxidation speed, lower electric resistivity( 64.24 $$\mu \Omega$$ cm), and negligible agglomeration effect, is recommended for industrial applications.

A simple robust method of synthesis of copper–silver core–shell nano-particle: evaluation of its structural and chemical properties with anticancer potency

A simple method of synthesis of a stable bimetallic copper–silver nano-particle (CuAg-NP) was developed by successive reduction of Cu(NO3)2 and AgNO3, using hydrazine hydrate as the reducing agent and gelatin and poly-vinyl pyrrolidone (PVP) as the capping agents. The round-shaped particles were of a core–shell structure with a core of Cu0 atoms surrounded by a shell of Ag0 atoms. The size and the mol. wt. of the NPs were (100 ± 10) nm and (820 ± 157) Kd, respectively; the particles were crystalline in nature and 90% of the precursors Cu(NO3)2 and AgNO3 were converted to the NPs. The particles were more toxic to cancer cells than normal cells; the dose of the NPs (4–5 μg ml−1), that killed about 75% of the different human cancer cell lines viz, HepG2 (liver cancer), A549 (lung cancer) and AGS (stomach cancer), killed only about 22.5% of the normal cell lines viz, WRL68 (liver) and WI38 (lung). Therefore, the NP may be developed as a potent anticancer drug in future. The more detailed study on the cytotoxicity of the CuAg-NP on the HepG2 cell line revealed that the particles caused cell cycle arrest in a G2/M phase, depolarization of mitochondrial membrane potential, translocation of phosphatidylserine residues from inner to outer leaflets of cell membrane and DNA degradation; these phenomena confirmed that the NP-induced cell death was apoptotic in nature.

Redox-Active AIEgen-Derived Plasmonic and Fluorescent Core@Shell Nanoparticles for Multimodality Bioimaging.

Multimodality imaging is highly desirable for accurate diagnosis by achieving high sensitivity, spatial-temporal resolution, and penetration depth with a single structural unit. However, it is still challenging to integrate fluorescent and plasmonic modalities into a single structure, as they are naturally incompatible because of significant fluorescence quenching by plasmonic noble-metal nanoparticles. Herein, we report a new type of silver@AIEgen (aggregation-induced emission luminogen) core-shell nanoparticle (AACSN) with both strong aggregated-state fluorescence of the AIEgen and distinctive plasmonic scattering of silver nanoparticles for multimodality imaging in living cells and small animals. The AACSNs were prepared through a redox reaction between silver ions and a redox-active AIEgen, which promoted synergistic formation of the silver core and self-assembly of the AIEgen around the core. The resulting AACSNs exhibited good biocompatibility and high resistance to environmental damage. As a result, excellent performance in fluorescence imaging, dark-field microscopy, and X-ray computed tomography-based multimodality imaging was achieved.

Toxicological Assessment of a Lignin Core Nanoparticle Doped with Silver as an Alternative to Conventional Silver Core Nanoparticles.

Elevated levels of silver in the environment are anticipated with an increase in silver nanoparticle (AgNP) production and use in consumer products. To potentially reduce the burden of silver ion release from conventional solid core AgNPs, a lignin-core particle doped with silver ions and surface-stabilized with a polycationic electrolyte layer was engineered. Our objective was to determine whether any of the formulation components elicit toxicological responses using embryonic zebrafish. Ionic silver and free surface stabilizer were the most toxic constituents, although when associated separately or together with the lignin core particles, the toxicity of the formulations decreased significantly. The overall toxicity of lignin formulations containing silver was similar to other studies on a silver mass basis, and led to a significantly higher prevalence of uninflated swim bladder and yolk sac edema. Comparative analysis of dialyzed samples which had leached their loosely bound Ag+, showed a significant increase in mortality immediately after dialysis, in addition to eliciting significant increases in types of sublethal responses relative to the freshly prepared non-dialyzed samples. ICP-OES/MS analysis indicated that silver ion release from the particle into solution was continuous, and the rate of release differed when the surface stabilizer was not present. Overall, our study indicates that the lignin core is an effective alternative to conventional solid core AgNPs for potentially reducing the burden of silver released into the environment from a variety of consumer products.

Silver microspheres coated with a molecularly imprinted polymer as a SERS substrate for sensitive detection of bisphenol A.

An efficient approach is demonstrated for preparing particles consisting of a silver core and a shell ofmolecularly imprinted polymer (Ag@MIP). The MIP is prepared byusing bisphenol A (BPA) as the template and 4-vinylpyridine as the functional monomer. The Ag@MIP fulfills a dual function in that the silver core acts as a SERS substrate, while the MIP allows for selective recognition of BPA. The Ag@MIP is characterized by scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, thermogravimetric analysis and Raman spectroscopy. The Raman intensity of Ag@MIP is higher than that of bare silver microspheres. The detection limit for BPA is as low as 10-9mol·L-1. Graphical abstract Schematic illustration of the preparation of silver microspheres coated with a molecularly imprinted polymer (Ag@MIPs) for detecting bisphenol A (BPA) by surface enhanced Raman scattering (SERS).

Tetrahedral (T) Closed-Shell Cluster of 29 Silver Atoms & 12 Lipoate Ligands, [Ag29(R-α-LA)12](3-): Antibacterial and Antifungal Activity.

Here we report on the identification and applications of an aqueous 29-atom silver cluster stabilized with 12 lipoate ligands, i.e. Ag29(R-α-LA)12 or (29,12), wherein R-α-LA = R-α-lipoic acid, a natural dithiolate. Its uniformity is checked by HPLC-ESI-MS and analytical ultracentrifugation, which confirms its small dimension (~3 nm hydrodynamic diameter). For the first time, this cluster has been detected intact via electrospray ionization mass spectrometry, allowing one to confirm its composition, its [3-] charge-state, and the 8-electron shell configuration of its metallic silver core. Its electronic structure and bonding, including T-symmetry and profound chirality in the outer shell, have been analyzed by DFT quantum-chemical calculations, starting from the known structure of a nonaqueous homologue. The cluster is effective against Methicillin-Resistant Staphylococcus aureus bacteria (MRSA) at a minimum inhibitory concentration (MIC) of 0.6 mg-Ag/mL. A preformed Candida albicans fungal biofilm, impermeable to other antifungal agents, was also inhibited by aqueous solutions of this cluster, in a dose-response manner, with a half-maximal inhibitory concentration (IC50) of 0.94 mg-Ag/mL. Scanning electron micrographs showed the post-treatment ultrastructural changes on both MRSA and C. albicans that are characteristic of those displayed after treatment by larger silver nanoparticles.

Quantitative and ultrasensitive detection of multiplex cardiac biomarkers in lateral flow assay with core-shell SERS nanotags

Rapid and sensitive quantification of multiplex proteins in a wide concentration range is challenging in high throughput analysis. Herein, we proposed a lateral flow assay (LFA) based on core-shell surface enhanced Raman scattering (SERS) nanotags for multiplex and quantitative detection of cardiac biomarkers for the early diagnosis of acute myocardial infarction (AMI). In practice, Raman dyes (RDs) were embedded into the interior-gap of silver core and gold shell nanoparticles (NPs) to form SERS nanotags as labels instead of gold colloids and three test lines were employed in the strip for the detection of three cardiac biomarkers, Myo, cTnI, and CK-MB, respectively. Due to the amplified signal of the SERS nanotags and the high surface area to volume ratio (SVR) of porous nitrocellulose (NC) membrane, ultrasensitive quantification of protein markers with wide linear dynamic range (LDR) was realized, which is crucial for the quick detection of multiplex biomarkers in the same sample without pretreatments at bedsides. This method makes it possible for LFA in point of care testing (POCT) to be comparable with chemiluminescence immunoassay (CLIA) used in labs.

Signatures of consolidated superparamagnetic and spin-glass behavior in magnetite-silver core-shell nanoparticles.

A detailed investigation of magnetization relaxation for silver-coated magnetite nanostructures with three different types of magnetic behavior in a single particle is presented. Magnetite nanoparticles of diameter ∼6.5 nm synthesized via single-phase emulsion were further coated with a silver shell of thickness ∼2 nm. The synthesized nanoparticles are found to be efficiently photoluminescent. The coating of silver generates a magnetically disordered spin layer at the interface of the magnetic core and the non-magnetic shell. This intermediate layer plays a significant role in the dynamical magnetic response of nanoparticles under an external magnetic field. We present detailed magnetic measurements such as field- and temperature-dependent dc magnetization with zero-field-cooled and field-cooled protocols, ac susceptibility and time decay of magnetization relaxation along with their analysis using various formalisms viz. Néel-Arrhenius, Vogel-Fulcher and power law models. The relaxation analysis suggests the consolidated presence of two characteristic relaxation times corresponding to the superparamagnetic and spin-glass behavior of silver-coated magnetite nanoparticles.

Study of the effect of varying core diameter, shell thickness and strain velocity on the tensile properties of single crystals of Cu–Ag core–shell nanowire using molecular dynamics simulations

Core–shell type nanostructures show exceptional properties due to their unique structure having a central solid core of one type and an outer thin shell of another type which draw immense attention among researchers. In this study, molecular dynamics simulations are carried out on single crystals of copper–silver core–shell nanowires having wire diameter ranging from 9 to 30 nm with varying core diameter, shell thickness, and strain velocity. The tensile properties like yield strength, ultimate tensile strength, and Young’s modulus are studied and correlated by varying one parameter at a time and keeping the other two parameters constant. The results obtained for a fixed wire size and different strain velocities were extrapolated to calculate the tensile properties like yield strength and Young’s modulus at standard strain rate of 1 mm/min. The results show ultra-high tensile properties of copper–silver core–shell nanowires, several times than that of bulk copper and silver. These copper–silver core–shell nanowires can be used as a reinforcing agent in bulk metal matrix for developing ultra-high strength nanocomposites.

On the Plasmonic Properties of Ag@SiO2@Graphene Core-Shell Nanostructures

This work reports on a study regarding the plasmonic properties of the Ag@SiO2@Graphene core-shell nanostructures, in the wavelength range of 0.3–2 μ m. Spherical and ellipsoidal geometries of the core-shell structure are proposed. The extinction efficiency is numerically simulated with several parameters being varied, including the chemical potential of the graphene shell, the radius of the silver spherical core, and the background materials of air and water, as well as the geometry of the ellipsoids. Two peaks are revealed in the extinction efficiency curve, which are attributed to the plasmonic resonance effect of the silver core and to that associated with the graphene shell, respectively. The results demonstrate that the plasmonic resonance wavelength of the peak that is induced in the graphene shell can be tuned in the wavelength range studied, by changing the value of the chemical potential. Based on the plasmonic characteristics revealed in this study, it is suggested that the core-shell structure of Ag@SiO2@Graphene be implemented in future designs of practical plasmonic devices.

Design considerations of super-directive nanoantennas for core-shell nanowires

The metallodielectric Yagi antenna showed high directivity in the visible range as compared with all dielectric nanoantennas. In this paper, two different configurations have been introduced and analyzed: slanted nanowire optical Yagi antenna and asymmetric core-shell nanoantenna. Both designs have an Ag core and Si shell. The numerical results are obtained using the 3D FDTD technique. The proposed nanoantennas show ultradirective radiation in the direction of propagation. It has been shown that, by varying the angle Θ of the slanted nanowire directors, the directivity of the nanoantenna is enhanced, and the beam width becomes narrow in the desired direction. The directivity is improved to 21.23 when Θ=18°, and the radiation efficiency is enhanced to 54% at a wavelength of 500 nm. Additionally, the asymmetric core-shell Yagi design enhanced the directivity to 22.4 at a wavelength of 500 nm, with an enhancement of 30% over the symmetric design. This improvement is attributed to the near-field intensity enhancement of the asymmetric core-shell design. The variation of the silver core position may be beneficial for various applications, including surface-enhanced Raman spectroscopy, energy harvesting, photodetection, and photovoltaics.

Zirconium(IV) oxide: New coating material for nanoresonators for shell-isolated nanoparticle-enhanced Raman spectroscopy

One tool that can be used for determining the structure and composition of surfaces of various materials (even in in situ conditions) is shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS). In SHINERS measurements, the surface under investigation is covered with a layer of surface-protected plasmonic nanoparticles, and then the Raman spectrum of the surface analysed is recorded. The plasmonic cores of the used core-shell structures act as electromagnetic nanoresonators, significantly locally enhancing the intensity of the electric field of the incident radiation, leading to a large increase in the efficiency of the generation of the Raman signal from molecules in the close proximity to the deposited SHINERS nanoresonators. A protective layer (from transparent dielectrics such as SiO2, Al2O3 or TiO2) prevents direct interaction between the plasmonic metal and the analysed surface (such interactions may lead to changes in the structure of the surface) and, in the case of plasmonic cores other than gold cores, the dielectric layer increases the chemical stability of the metal core. In this contribution, we show for the first time that core-shell nanoparticles having a silver core (both a solid and hollow one) and a shell of zirconium(IV) oxide are very efficient SHINERS nanoresonators that are significantly more stable in acidic and alkaline media than the silver-silica core-shell structures typically used for SHINERS experiments.

Solvent-assisted in situ synthesis of cysteamine-capped silver nanoparticles

Silver nanoparticles offer a huge potential for biomedical applications owing to their exceptional properties and small size. Specifically, cysteamine-capped silver nanoparticles could form the basis for new anticancer therapies combining the cytotoxic effect of the silver core with the inherent antitumor activity of cysteamine, which inhibit cancer cell proliferation and suppress invasion and metastasis. In addition, the capability of the cysteamine coating monolayer to couple a variety of active principles and targeting (bio)molecules of interest proves key to the tailoring of this platform in order to exploit the pathophysiology of specific tumor types. Nevertheless, the chain length and conformational flexibility of cysteamine, together with its ability to attach to the surface of silver nanoparticles via both the thiol and the amine group, have made the in situ synthesis of these particles an especially challenging task. Herein we report a solvent-assisted in situ synthesis method that solves this problem. The obtained nanoparticles have been fully characterized by UV–visible absorption spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, electron diffraction measurement, high resolution transmission electron microscopy, scanning transmission electron microscopy, energy dispersive x-ray spectroscopy nanoanalysis, and dynamic light scattering measurement. Our synthesis method achieves extremely high yield and surface coating ratio, and colloidal stability over a wide range of pH values including physiological pH. Additionally, we have demonstrated that cysteamine-capped nanoparticles obtained by this method can be conjugated to an antibody for active targeting of the epidermal growth factor receptor, which plays an important role in the pathogenesis and progression of a wide variety of tumors, and induce cell death in human squamous carcinoma cells. We believe this method can be readily extended to combinations of noble metals and longer chain primary, secondary, ternary or even quaternary aminethiols.

Preparation and characterization of Ag@C composites with hexagon silver core and controllable carbon shell for surface-enhanced Raman scattering

Here, novel and stable core–shell silver–carbon nanocomposites (Ag@CSs) were obtained using glucose as the carbon source and stabilizer, silver nitrate as the silver source, and trioctylamine (TOA) as the soft template and extractant. It is worth mentioning that the shape of the silver core shows the hexagon shape, and we consider that TOA and glucose selectively adsorb the Ag (111) crystal face resulting in this growth pattern of the silver core. Owing to the enhanced local field effect around their sharp corners and edges, such structure exhibits superior properties for the surface-enhanced Raman scattering (SERS) enhancement. The hydrothermal carbon shell not only effectively avoids the agglomeration of Ag nanoparticles core, but also serves as a protective layer of the SERS active nanostructure during the whole course of the experiment. In addition, the thickness of the loose shell was significantly reduced after the product was stored in ethanol solution for a period of time. It is found that dropped cast probe molecules onto Ag@CSs have a lower SERS activity, while that immersed in the probe molecular solution for a period of time have a higher SERS activity, indicating that the detection of the probe molecules using this Ag@CSs substrate may require an interactive process. The results show that the as-obtained Ag@CSs hold tremendous potential for SERS applications for its long-term stability and superior SERS performance.

Plasmonic Near-Field Localization of Silver Core-Shell Nanoparticle Assemblies via Wet Chemistry Nanogap Engineering.

Silver nanoparticles are widely used in the field of plasmonics because of their unique optical properties. The wavelength-dependent surface plasmon resonance gives rise to a strongly enhanced electromagnetic field, especially at so-called hot spots located in the nanogap in-between metal nanoparticle assemblies. Therefore, the interparticle distance is a decisive factor in plasmonic applications, such as surface-enhanced Raman spectroscopy (SERS). In this study, the aim is to engineer this interparticle distance for silver nanospheres using a convenient wet-chemical approach and to predict and quantify the corresponding enhancement factor using both theoretical and experimental tools. This was done by building a tunable ultrathin polymer shell around the nanoparticles using the layer-by-layer method, in which the polymer shell acts as the separating interparticle spacer layer. Comparison of different theoretical approaches and corroborating the results with SERS analytical experiments using silver and silver-polymer core-shell nanoparticle clusters as SERS substrates was also done. Herewith, an approach is provided to estimate the extent of plasmonic near-field enhancement both theoretically as well as experimentally.

Molecular Tilting Alignment on Ag@C Nanocubes Monitored by Temperature-Dependent Surface Enhanced Raman Scattering

Core@shell Ag@C nanocubes (NCs) with a cubic silver core (~60 nm of side length) and a coating of ultrathin amorphous carbon (~4 nm) have been synthesized on a large scale by a one-pot hydrothermal method. The carbon layer not only protects the Ag@C nanocubes from oxidation under hydrothermal condition, but also stabilizes the structure of Ag cores. Considering that optical properties of nanostructured metals strongly depend on the temperature for SERS measurement, in this work we systemically investigate the relationship between the orientation of molecules adsorbed on Ag@C NCs and temperature by SERS spectra. Results suggest that the adsorbed 4-MBA molecules prefer a flat orientation on the NC surface with temperature decreasing. In addition, Ag@C NCs after one-year storage in water still maintain high SERS-active capability. Our synthesized Ag@C NCs with excellent and stable optical properties can be potentially applied in the field of sensor and ultrasensitive spectral analysis.

Core–Shell Nanoparticles Containing Peptide Dendrimers

Dealloying of bimetallic gold core–silver shell nanoparticles (NPs) is achieved using peptide dendrimers from generation 1 to generation 3. The resulting NPs exhibit optical properties characteristic of Au/Ag core–shell NPs with weak surface plasmon resonance interactions between the core and shell. Transmission electron microscopy and x-ray photoelectron spectroscopy of the core–shell NPs exhibit a size and composition dependence on the dendrimer generation number. Rutherford backscattering spectrometric analyses of core–shell NPs containing dendrimer innerlayer indicates that the NPs are consisting of discrete domains of Ag–shell and Au–core.