Silver Core Research Articles

Magnetic and optical properties of Ag@SiO2-FITC-Fe3O4 hybrid nanoparticles

• New magnetic/fluorescent nanoparticles were synthesized. • The silver core led to a maximum 4-fold enhanced fluorescence of fluorophore. • Maximum enhancement factor was obtained when metal-fluorophore distance is 5 nm. • Magnetism and fluorescence appeared simultaneously for nanoparticles in solution. Nanoparticles composed of a silver core coated with a silica shell (Ag@SiO 2 ) were prepared. A dye, fluorescein isothiocyanate (FITC), was further encapsulated during the growth of a second silica shell onto Ag@SiO 2 nanoparticles. The proximity of silver nanoparticles led to a 4-fold maximal enhancement in the fluorescence of FITC when the first silica shell thickness was set at 5 nm. After amino-functionalization of Ag@SiO 2 -FITC nanoparticles, iron oxide nanoparticles were bonded to their surface. The magnetic and metal-enhanced fluorescence properties appeared simultaneously when Ag@SiO 2 -FITC-Fe 3 O 4 hybrid nanoparticles were dispersed in a solution.

A Nano-Silver Enhancement Effect on the Luminescence of a Ligand–Eu3+ Complex via a SiO2 Spacer

Luminescent rare earth complex (REC) nanocomposites, Eu(TTA)3Phen attached onto Ag@SiO2 nanoshells, were fabricated by facile wet chemistry and self-assembly techniques. Transmission electron microscopy, and fourier transform infrared and UV–Vis spectroscopy were used to investigate the step-by-step fabrication. The luminescence of REC was significantly enhanced using a silver core (size: 45 nm) surrounded by a 20-nm thick silica shell. Thicker or thinner silica shells afforded tuning of the metal-enhanced luminescence. The thiophene-TTA-containing REC fluorophore was able to etch the silver core, resulting in hollow silica shells, consequently displaying no luminescence enhancing capabilities. The etching efficiency was proportional to the concentration of Eu(TTA)3Phen, and decreased with increasing shell thickness.

SERS and catalytically active Ag/Pd nanoparticles obtained by combining laser ablation and galvanic replacement

Bimetallic Ag/Pd nanoparticles were fabricated by laser ablation of a silver target in water and successive addition of palladium nitrate to promote a partial galvanic replacement of silver with palladium. The obtained nanoparticles, as shown by a microscopic investigation coupled with EDX and SAED analysis, exhibit a silver core, able to produce SERS enhancement, and a Pd cloudy shell at the surface that can interact with organic molecules in catalytic reactions. The test was carried out using as a molecular probe an aromatic nitroderivative, which, by adsorption on the metal substrate, undergoes an almost total reduction to azoderivate, as evidenced by the comparison between the SERS spectra recorded on pure Ag and Ag@Pd nanoparticles.

Synthesis of Triple‐Layered Ag@Co@Ni Core–Shell Nanoparticles for the Catalytic Dehydrogenation of Ammonia Borane

Triple-layered Ag@Co@Ni core-shell nanoparticles (NPs) containing a silver core, a cobalt inner shell, and a nickel outer shell were formed by an in situ chemical reduction method. The thickness of the double shells varied with different cobalt and nickel contents. Ag0.04 @Co0.48 @Ni0.48 showed the most distinct core-shell structure. Compared with its bimetallic core-shell counterparts, this catalyst showed higher catalytic activity for the hydrolysis of NH3 BH3 (AB). The synergetic interaction between Co and Ni in Ag0.04 @Co0.48 @Ni0.48 NPs may play a critical role in the enhanced catalytic activity. Furthermore, cobalt-nickel double shells surrounding the silver core in the special triple-layered core-shell structure provided increasing amounts of active sites on the surface to facilitate the catalytic reaction. These promising catalysts may lead to applications for AB in the field of fuel cells.

Synthesis and optical absorption of Ag/CdS core/shell plasmonic nanostructure

The Ag/CdS core/shell nanoparticles are synthesized by a facile method. The synthesis steps are simple and easy to be manipulated. The core/shell nanostructures are characterized by the transmission electron microscopy (TEM), X-ray diffraction (XRD), and UV–vis spectrometry techniques. Compared with bare Ag and CdS nanoparticles, the optical absorption of Ag/CdS composite nanostructures is greatly enhanced in a wide range of visible light. It can also be demonstrated in the simulations based on DDA method. The enhanced absorption of light is mainly due to the localized surface plasmon resonance (LSPR) effect excited on silver core. The optical response of such core/shell nanostructures is extended to longer wavelengths.

The effect of sulfur covalent bonding on the electronic shells of silver clusters

The nature of the bonding in Ag(n)S(m)(0∕-) clusters, n = 1-7; m = 1-4, has been analyzed to understand its effect on the electronic shell structure of silver clusters. First-principle investigations reveal that the sulfur atoms prefer 2 or 3-coordinate sites around a silver core, and that the addition of sulfur makes the planar structures compact. Molecular orbital analysis finds that the 3p orbitals of sulfur form a bonding orbital and two weakly bonding lone pairs with silver. We examine the electronic shell structures of Ag6Sm, which are two electrons deficient of a spherical closed electronic shell prior to the addition of sulfur, and Ag7S(m)(-) clusters that contain closed electronic shells prior to the addition of sulfur. The Ag6S4 cluster has a distorted octahedral silver core and an open shell with a multiplicity of 3, while the Ag7S(n_(-) clusters have compact geometries with enhanced stability, confirming that the clusters maintain their electronic shell structure after bonding with sulfur.

Surface-Enhanced Raman Scattering Substrates Based on Self-Assembled PEGylated Gold and Gold–Silver Core–Shell Nanorods

For routine laboratory practice, surface-enhanced Raman scattering (SERS) spectroscopy must be simple, inexpensive, stable for a long time, and reproducible. In this study, we mixed 1 μL of PEGylated silver-coated gold nanorods (Au–Ag NRs) with 1 μL of Raman reporters to obtain, after deposition on a silicon wafer and drying at room temperature for 5 min, a self-assembled NR monolayer with incorporated Raman molecules. In addition, PEGylated NR powders were fabricated and used for SERS in two options. In one, they were used to prepare SERS colloids with a desired NR concentration in a matter of seconds; in the other, they were directly dissolved in a drop of analyte and were then deposited on a silicon wafer. We investigated the SERS spectra of rhodamine 6G (R6G) and the analytical enhancement factor (AEF) as a function of silver shell thickness and NR concentration at 633 nm laser excitation. A very thin (∼2 nm) silver coating of Au NRs was sufficient to increase the AEF from 103 for Au NRs to 2.5 × 104 ...

The influence of silver core position on enhanced photon absorption of single nanowire α-Si solar cells

Photon absorption of single nanowire solar cells can be modulated by metallic core. Silver core was integrated into α-Si single nanowire solar cells (SNSCs), and the influence of silver core position on enhanced photon absorption efficiency and the short circuit current (J(sc)) was investigated. The finite-difference time domain (FDTD) method was used to rigorously solve Maxwell's equations in two dimensions. The J(sc) decreases when the silver core is integrated into the center of nanowire. However, the photon absorption efficiencies and J(sc) could be enhanced by tuning the core position in the nanowire. J(sc) enhancement of 21.4% is achieved when nanowire radius R is 190 nm, core radius r is 30 nm, the silver core is located in the negative Y-axis and the distance from the center of silver core to the origin d is 102 nm under realistic solar illumination.

Acoustic Vibrations of Au Nano-Bipyramids and their Modification under Ag Deposition: a Perspective for the Development of Nanobalances

We investigated the acoustic vibrations of gold nanobipyramids and bimetallic gold-silver core-shell bipyramids, synthesized by wet chemistry techniques, using a high-sensitivity pump-probe femtosecond setup. Three modes were observed and characterized in the gold core particles for lengths varying from 49 to 170 nm and diameters varying from 20 to 40 nm. The two strongest modes have been associated with the fundamental extensional and its first harmonic, and a weak mode has been associated with the fundamental radial mode, in very good agreement with numerical simulations. We then derived linear laws linking the periods to the dimensions both experimentally and numerically. To go further, we investigated the evolution of these modes under silver deposition on gold core bipyramids. We studied the evolution of the periods of the extensional modes, which were found to be in good qualitative agreement with numerical simulations. Moreover, we observed a strong enhancement of the radial mode amplitude when silver is deposited: we are typically sensitive to the deposition of 40 attograms of silver per gold core particle. This opens up possible applications in the field of mass sensing, where metallic nanobalances have an important role to play, taking advantage of their robustness and versatility.

Layer-by-layer self-assembly of plexcitonic nanoparticles

Colloidal suspensions of multilayer nanoparticles composed of a silver core, a polyelectrolyte spacer layer (inner shell), and a J-aggregate cyanine dye outer shell have been prepared for the first time. Absorption properties of the colloid were measured in the visible region. This multilayer architecture served as a framework for examining the coupling of the localized surface plasmon resonance exhibited by the silver core with the molecular exciton exhibited by the J-aggregate outer shell. The polyelectrolyte spacer layer promotes the formation of an excitonic J-aggregate while serving as a means of controlling the plasmon-exciton (i.e. plexciton) coupling strength through changing the distance between the core and the shell. An analytical expression based on Mie Theory and the Transfer Matrix Method was obtained for describing the optical response of these multilayered nanostructures. Computational and experimental results indicate that the absorption wavelength of the J-aggregate form of the dye is dependent on both the distance of the dye layer from the silver core and the degree of dye aggregation.

Optimization of silver-dielectric-silver nanoshell for sensing applications

In this paper, resonance light scattering (RLS) properties of a silver-dielectric-silver nanoshell, based on quasi-static approach and plasmon hybridization theory, are investigated. Scattering spectrum of silver-dielectric-silver nanoshell has two intense and clearly separated RLS peaks and provides a potential for biosensing based on surface plasmon resonance and surface-enhanced Raman scattering. The two RLS peaks in silver-dielectric-silver nanoshell are optimized by tuning the geometrical dimensions. In addition, the optimal geometry is discussed to obtain the high sensitivity of silver-dielectric-silver nanoshell. As the silver core radius increases, the sensitivity of silver-dielectric-silver nanoshell decreases whereas increasing the middle dielectric thickness increases the sensitivity of silver-dielectric-silver nanoshell.

One-pot synthesis of various Ag–Au bimetallic nanoparticles with tunable absorption properties at room temperature

This report describes the formation of gold-coated silver bimetallic nanoparticles prepared by the one-pot synthetic approach which involves the subsequent reduction of silver and gold ions at ambient conditions. The reduction of silver ions by excess L-ascorbic acid initially led to the formation of silver cores. This step was followed by the addition of gold ions into the preformed cores, resulting in the formation of silver-core gold-shell type bimetallic nanoparticles at room temperature. This process systematically allowed for the formation of various bimetallic nanoparticles which exhibited tunable absorption properties corresponding to the visible and near-IR regions. The thickness of the gold shells and the diameter of the silver-core nanoparticles were readily controlled; the morphological and structural properties of the resulting bimetallic nanoparticles were thoroughly analyzed by SEM/TEM, DLS, and UV–Vis spectrophotometry. The overall results demonstrated not only that these gold-coated silver nanoparticles were reliably prepared by our one-pot synthetic approach, but also that their optical properties were tunable in the visible and near-IR areas as a function of the core size and shell thickness.

Tuning Structural and Optical Properties of Thiolate-Protected Silver Clusters by Formation of a Silver Core with Confined Electrons

We present a systematic theoretical investigation of the structural and optical properties of thiolate-protected silver clusters with the goal to design species exhibiting strong absorption and fluorescence in the UV–vis spectral range. We show that the optical properties can be tuned by creating systems with different counts of confined electrons within the cluster core. We consider liganded silver complexes with n silver atoms (Agn) and x ligands (Lx) in anionic complexes [AgnLx]− with L = SCH3. Variation of the composition ratio gives rise to systems with (i) zero confined electrons for x = n + 1, (ii) two confined electrons for x = n – 1, and (iii) four confined electrons for x = n – 3. We show that the number of confined electrons within the cluster core and the geometric structure of the latter are responsible for the spectral patterns, giving rise to intense absorption transitions and fluorescence in the visible or even infrared range. Our results open a perspective for the rational design of stabl...

Fluorescence enhancement of [formula omitted] by core–shell Ag@SiO2 nanocomposites

Enhancement of the light emission of dye molecules (Ru(bpy)32+) was studied by coating dye-doped SiO2 layer on Ag core. The enhancement ratio was found to be relative to the thickness of dye-doped silica layer. The core–shell Ag@dye-SiO2 nanocomposites have the strongest fluorescence intensities when the thickness of dye-SiO2 layer was tuned to 10nm. It was found that an 11-fold enhancement of fluorescence signal was realized with Ag@dye-SiO2 nanoparticles, compared to the sample without silver core.

Absorption and Scattering of Light by Hybrid Metal/J-Aggregate Nanoparticles: Plasmon–Exciton Coupling and Size Effects

We report the results of our theoretical studies of the optical properties of hybrid nanoparticles consisting of the metal core covered with molecular J-aggregates. We evaluate the cross sections of absorption and scattering of light by such particles on the basis of the extended Mie theory for two concentric spheres with material dielectric functions that take into account the size effect associated with scattering of free electrons from the core/shell interface. We carry out our calculations in a wide range of light wavelengths and geometrical parameters of the composite system for silver and gold core and for a J-aggregate shell composed of different cyanine dyes. The results obtained demonstrate the quite different behavior of the extinction spectra of such particles caused by the different strengths of interaction between the Frenkel exciton and the dipolar or multipolar plasmons. We pay particular attention to the investigation of spectral peak positions associated with the eigenfrequencies of hybrid modes in the system and peak intensities as functions of reduced oscillator strength in the molecular J-band for various relationships between the core radius and shell thickness. This provides an efficient means for the explanation of the main features in the optical properties of metal/J-aggregate nanoparticles and can be used for an effective control of the plasmon–exciton coupling strength in such hybrid complexes.

Meditating Metal Coenhanced Fluorescence and SERS Around Gold Nanoaggregates in Nanosphere as Bifunctional Biosensor for Multiple DNA Targets

Gold nanoparticles (Au NPs) are very attractive candidate nanoparticles in biological assay because of their high chemical stabilities, high homogeneities, good biocompatibilities, and low toxicities. However, molecular beacon assays via encapsulating the combined fluorescence or surface-enhanced Raman scattering (SERS) signals of reporters and Au NPs in nanobarcodes particles usually suffer from fluorescence quenching or weak Raman enhancement when Au NPs are employed (especially with size smaller than 15 nm). Herein, we present a new design of simultaneously realizing metal-enhanced fluorescence and coenhanced surface-enhanced Raman scattering by facilely embedding Ag nanoparticle into the shell of two kinds of Au nanoaggregate (5 and 10 nm), meanwhile, fluorophore is located between the silver core and gold nanoparticle layers and the distance among them is adjusted by SiO2 spacer (Ag@first SiO2 spacer@FiTC+SiO2@second SiO2 spacer@Au nanoaggregate). In this architecture, Ag nanoparticle not only is utilized as an efficient fluorescence enhancer to overcome the common fluorescence quenching around Au nanoaggregates but also behaves like a mirror. Thus, incident light that passes through the SERS-active Au nanoaggregate and the intervening dielectric layer of SiO2 could be reflected multiply from the surface of Ag nanoparticle and coupled with the light at the nanogap between the Au nanoaggregates to further amplify Raman intensity. This results in enhancement factors for fluorescence and SERS ~1.6-fold and more than 300-fold higher than the control samples without silver core under identical experimental conditions, respectively. Moreover, fluorophore and SERS reporters are assembled onto different layers of the concentric hybrid microsphere, resulting in a feasible fabrication protocol when a large number of agents need to be involved into the dual-mode nanobarcodes. A proof-of-concept chip-based DNA sandwich hybridization assay using genetically modified organisms as a model system has been investigated based on the concentric hybrid microsphere. The high specificity and sensitivity of the assays suggest that the new architecture has a potential for various bioanalytical applications and provides opportunities for other similar metal nanoparticles to realize coenhancement effect.

Synthesis, characterization, and in vivo efficacy of shell cross-linked nanoparticle formulations carrying silver antimicrobials as aerosolized therapeutics.

The use of nebulizable, nanoparticle-based antimicrobial delivery systems can improve efficacy and reduce toxicity for treatment of multi-drug-resistant bacteria in the chronically infected lungs of cystic fibrosis patients. Nanoparticle vehicles are particularly useful for applying broad-spectrum silver-based antimicrobials, for instance, to improve the residence time of small-molecule silver carbene complexes (SCCs) within the lung. Therefore, we have synthesized multifunctional, shell cross-linked knedel-like polymeric nanoparticles (SCK NPs) and capitalized on the ability to independently load the shell and core with silver-based antimicrobial agents. We formulated three silver-loaded variants of SCK NPs: shell-loaded with silver cations, core-loaded with SCC10, and combined loading of shell silver cations and core SCC10. All three formulations provided a sustained delivery of silver over the course of at least 2–4 days. The two SCK NP formulations with SCC10 loaded in the core each exhibited excellent antimicrobial activity and efficacy in vivo in a mouse model of Pseudomonas aeruginosa pneumonia. SCK NPs with shell silver cation-load only, while efficacious in vitro, failed to demonstrate efficacy in vivo. However, a single dose of core SCC10-loaded SCK NPs (0.74 ± 0.16 mg Ag) provided a 28% survival advantage over sham treatment, and administration of two doses (0.88 mg Ag) improved survival to 60%. In contrast, a total of 14.5 mg of Ag+ delivered over 5 doses at 12 h intervals was necessary to achieve a 60% survival advantage with a free-drug (SCC1) formulation. Thus, SCK NPs show promise for clinical impact by greatly reducing antimicrobial dosage and dosing frequency, which could minimize toxicity and improve patient adherence.

Plasmonic Biosensor Based on Triangular Au/Ag and Au/Ag/Au Core/Shell Nanoprisms onto Indium Tin Oxide Glass

Gold–silver core–shell triangular nanoprisms (Au/AgTNPs) were grown onto transparent indium tin oxide (ITO) thin film-coated glass substrate through a seed-mediated growth method without using peculiar binder molecules. The resulting Au/AgTNPs were characterized by scanning electron microscopy, atomic force microscopy, X-ray diffraction, UV–vis spectroscopy, and cyclic voltammograms. The peak of dipolar plasmonic resonance was located at near infrared region of ∼700 nm, which showed the refractive index (RI) sensitivity of 248 nm/RIU. Moreover, thin gold shells were electrodeposited onto the surface of Au/AgTNPs in order to stabilize nanoparticles. Compared with the Au/AgTNPs, this peak of localized surface plasmon resonance (LSPR) was a little red-shift and decreased slightly in intensity. The refractive index sensitivity was estimated to be 287 nm/RIU, which showed high sensitivity as a LSPR sensing platform. Those triangular nanoprisms deposited on the ITO substrate could be further functionalized to fabricate LSPR biosensors. Results of this research show a possibility of improving LSPR sensor by using core–shell nanostructures.

Direct Experimental Evidence of Nucleation and Kinetics Driven Two-Dimensional Growth of Core–Shell Structures

We report the appearance of different anisotropic one-dimensional (1D) and two-dimensional (2D) gold (Au) core–silver (Ag) shell nanostructures in a single reaction environment. High-resolution transmission electron microscopy (HRTEM) images taken from the core region of a core–shell nanostructure revealed the prominent presence of the hexagonal-shaped gold seed leading to formation of a triangular final particle. The HRTEM studies provide the direct experimental evidence of the “silver halide” model proposed by Sigmund et al. (Lofton, C.; Sigmund, W. Adv. Funct. Mater.2005, 15, 1197–1208) to explain the kinetic growth mechanism behind their formation. It is important that this information cannot be identified from a single composite nanoparticle due to the lack of atomic number (Z) contrast difference. We have studied energy-dispersive X-ray line profile spectra and elemental mapping using the high-angle annular dark-field scanning/transmission electron microscopy (STEM-HAADF) technique corresponding to the Au-M and Ag-K energies from the similar core–shell structures. This confirms the composition of the core to be made of gold and that of the shell of silver. The line profile along the relative thickness map of a hexagonal and triangular nanoplate obtained using energy-filtered TEM indicates the formation of nearly uniform 2D structures. The nearly equal thicknesses of the core and outside shell of a core–shell nanoplate measured using electron energy loss spectroscopy in STEM mode also confirm the 2D growth of a gold seed forming a triangular core–shell nanoplate.

Geometrical parameters effects on local electric field enhancement of silver-dielectric-silver multilayer nanoshell

The local electric field enhancement at different points of silver-dielectric-silver nanoshell is investigated using quasi-static theory. Because of the symmetric and anti-symmetric coupling between surface plasmon of inner silver core and outer silver shell, the local electric field spectrum of silver-dielectric-silver has two distinct peaks at resonance wavelengths. The silver core size and middle dielectric thickness affect the local electric field enhancement at different points of silver-dielectric-silver nanoshell. Increasing the silver core radius always leads to blue shift of shorter resonance wavelength and red shift of longer resonance wavelength. We observed two distinct local electric field peaks, which are corresponded to the symmetric and anti-symmetric coupling between inner and outer surface plasmons. In a system with thick silver shell, local electric field enhancement is greater than a system with thin silver shell. However, the local electric field variations as a function of silver core radius in both systems are different at different points of nanoshell. The effects of the dielectric thickness variations on local electric field are different from those from silver core size variations. As the dielectric thickness is about 3 nm, the highest local electric field enhancement occurs at the surface of the inner silver core, where the symmetric and anti-symmetric modes are mixed together.