Silver Core Shell Nanoparticles Research Articles

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.

Plasmon-Enhanced Performance of an Array of Core-Shell Silver Nanoparticles Photodeposited onto a Titanium Dioxide Layer

A plasmonic photocatalytic reactor which composed of a periodic array of core-shell silver nanoparticles (CSSNPs) photodeposited onto a Titanium Dioxide (TiO2) thin film in a multilayer rotating-disk system was numerically investigated by using three-dimensional finite element method. Results show that the proposed structure can exhibit much higher photocalytic activity in a broad range of incident angle of light that are not observed for the same counterpart without the CSSNPs on the SiO2 surface. The enhanced electric field distribution and intensity could be expanded as the inner diameter of CSSNPs and incident angle of light increased.

An ultrasensitive label-free electrochemical immunosensor based on signal amplification strategy of multifunctional magnetic graphene loaded with cadmium ions.

Herein, a novel and ultrasensitive label-free electrochemical immunosensor was proposed for quantitative detection of human Immunoglobulin G (IgG). The amino functionalized magnetic graphenes nanocomposites (NH2-GS-Fe3O4) were prepared to bond gold and silver core-shell nanoparticles (Au@Ag NPs) by constructing stable Au-N and Ag-N bond between Au@Ag NPs and -NH2. Subsequently, the Au@Ag/GS-Fe3O4 was applied to absorb cadmium ion (Cd2+) due to the large surface area, high conductivity and exceptional adsorption capability. The functional nanocomposites of gold and silver core-shell magnetic graphene loaded with cadmium ion (Au@Ag/GS-Fe3O4/Cd2+) can not only increase the electrocatalytic activity towards hydrogen peroxide (H2O2) but also improve the effective immobilization of antibodies because of synergistic effect presented in Au@Ag/GS-Fe3O4/Cd2+, which greatly extended the scope of detection. Under the optimal conditions, the proposed immunosensor was used for the detection of IgG with good linear relation in the range from 5 fg/mL to 50 ng/mL with a low detection limit of 2 fg/mL (S/N = 3). Furthermore, the proposed immunosensor showed high sensitivity, special selectivity and long-term stability, which had promising application in bioassay analysis.

Facile one pot synthesis of core shell Ag@SiO2 nanoparticles for catalytic and antimicrobial activity

Silica core shell silver nanoparticles (Ag@SiO2 NPs) have been prepared by a one step synthesis in an eco-friendly way. Biological fermented product, i.e. whisky was used as a reducing agent for silver ions and as a catalyst for the formation of silica shell on silver nanoparticles (AgNPs). The structural and morphological studies were done by various analytical techniques to reveal its crystalline nature and core-shell structure. The catalytic activity of Ag@SiO2 NPs for the reduction of mixture of 4-nitrophenol (4-NP) and rhodamine-B (Rh-B) in presence of NaBH4 and its reusability are demonstrated. The antibacterial activity of Ag@SiO2 NPs against Escherichia coli (E. coli), Bacillus cereus (B. cereus), and Staphylococcus aureus (S. aureus) was studied.

Synthesis of large uniform gold and core–shell gold–silver nanoparticles: Effect of temperature control

The temperatures of nucleation and growth for gold and silver nanoparticles are quite close to each other in citrate-based seeded-growth synthesis. Hence, thorough temperature control during the synthesis of gold and gold–silver core–shell nanoparticles is expected to improve the yield of uniform non-aggregated nanoparticles suitable for selective contrasting of surface defects. Gold and gold–silver core–shell nanoparticles of size ranging from 20 to 160 nm were synthesized using various means of temperature control. The synthesized nanoparticles were characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS) and UV–Vis spectroscopy. Model nanocracks were milled on pipeline steel specimen by focused ion beam (FIB). It was found that to produce large uniform core–shell nanoparticles, thorough temperature control is required during formation of the gold seeds and the silver shell. Moreover, the synthesized nanoparticles were used for selective contrasting of defects on metal surface.

Core–shell gold–silver nanoparticles based impedimetric immunosensor for cancer antigen CA125

We report a simple and fast assay for cancer antigen CA125 quantification using gold–silver core–shell nanoparticles for ovarian cancer diagnosis and prognosis. The impedimetric analysis of CA125 using label-free and reagentless immunosensor could be used done in 20min. Furthermore, the directed immobilization of antibody onto the core–shell nanoparticles enabled linear response upto 1–150IU/mL (r2=0.994) as opposed to the maximum linear response of 1.0–100.0IU/mL reported for impedimetric immunosensors till date. The fabricated immunosensor displayed tolerable interference of 2.0–5% from serum components and retained 90% stability up to 20 days. Moreover, sensitivity of immunosensor fabricated using Au–Ag nanoparticles (190ΩIU−1mLcm−2) was almost three times that of gold nanoparticles based immunosensor (59ΩU−1mLcm−2).

Green Synthesized 3 Hexyne Conjugated Core–Shell Silver Nanoparticles Interferes Peptidoglycan in Inhibiting Multidrug Resistant Pathogens

Green Synthesized 3 Hexyne Conjugated Core–Shell Silver Nanoparticles Interferes Peptidoglycan in Inhibiting Multidrug Resistant Pathogens

High-value utilization of egg shell to synthesize Silver and Gold–Silver core shell nanoparticles and their application for the degradation of hazardous dyes from aqueous phase-A green approach

The common household material, egg shell of Anas platyrhynchos is utilized for the synthesis of Silver and Gold–Silver core shell nanoparticles using greener, environment friendly and economic way. The egg shell extracts were acting as a stabilizing and reducing agents. This method avoids the use of external reducing and stabilizing agents, templates and solvents. The effects of various reaction parameters, such as reaction temperature, concentration in the formation of nanoparticles have also been investigated. The compositional abundance of gelatin may be envisaged for the effective reductive as well as stabilizing potency. The mechanisms for the formation of NPs have also been presented. The synthesized Ag NPs formed were predominantly spherical in nature with an average size of particles in the range of 6–26nm. While, Au–Ag core shell nanoparticles formed were spherical and oval shaped, within a narrow size spectrum of 9–18nm. Both the Ag NPs Au-and Ag core shell nanoparticles showed characteristic Bragg’s reflection planes of fcc structure and surface plasmon resonance at 430nm and 365nm, respectively.The NPs were utilized for the removal of toxic and hazardous dyes, such as Rose Bengal, Methyl Violet 6 B and Methylene Blue from aqueous phase. Approximately 98.2%, 98.4% and 97% degradations of Rose Bengal, Methyl Violet 6 B, and Methylene Blue were observed with Ag NPs, while the percentage degradation of these dyes was 97.3%, 97.6% and 96% with Au–Ag NPs, respectively. Therefore, the present study has opened up an innovative way for synthesizing Ag NPs and Au–Ag bimetallic nanostructures of different morphologies and sizes involving the utilization of egg shell extract. The high efficiency of the NPs as photocatalysts has opened a promising application for the removal of hazardous dyes from the industrial effluents.

Preparation of nickel–silver core–shell nanoparticles by liquid-phase reduction for use in conductive paste

Nickel–silver (Ni–Ag) core–shell nanoparticles (NPs) were prepared by depositing Ag on Ni nanocores using the liquid-phase reduction technique in aqueous solution, and their properties were characterised using various experimental techniques. The core–shell NPs had good crystallinity, and the thicknesses of the Ag nanoshells could be tuned effectively. The oxidation resistance of the Ag surface and the electroconductive properties of the Ni core allowed these Ni–Ag core–shell NPs to be used in a conductive paste. Thick films composed of Ni–Ag core–shell NPs were screen-printed on a polycrystalline silicon substrate then sintered at temperatures ranging from 500 °C to 800 °C. Stable resistivity was obtained when the sintering temperature was higher than 650 °C, and the electrical properties of the Ni–Ag core–shell paste were close to those of pure Ag paste. Thus, the Ni–Ag NPs can partly replace pure Ag NPs in conductive pastes.

Tailored “Sandwich” Strategy in Surface Enhanced Raman Scattering: Case Study with para-Phenylenediamine and Application in Femtomolar Detection of Melamine

Herein, we have implemented a modified sandwich strategy for surface enhanced Raman scattering (SERS) studies aimed at the accomplishment of remarkably enhanced vibrational signatures from preferred Raman probes. Here, para-phenylenediamine (or PDA) has been selected as the test molecule which can concurrently bind to two metal surfaces with its two terminal amino (−NH2) groups. We have deliberately placed this molecule in the nanogaps found in between a nanostructured silver film/island and gold core–silver shell nanoparticles using a tailormade approach. The whole method of fabrication of this sandwich-type assembly follows a simple colloidal chemistry route. We observed highly enhanced and well resolved Raman signals from the PDA molecule in this sandwich (i.e., nanostructured Ag-film@PDA@Auc-Ags) assembly. The spectral characteristics were also compared with other modes of assembly/association of the molecule in different Raman active plasmonic environments, and from all these comparative outcomes, we...

Core–shell silver nanoparticles for optical labeling of cells

Silver nanoparticles have been modified with self-assembled monolayers of hydroxyl-terminated long chain thiols and encapsulated with a silica shell. The resulting core–shell nanoparticles were used as optical labels for cell analysis using flow cytometry and microscopy. The excitation of plasmon resonances in nanoparticles results in strong depolarized scattering of visible light, permitting detection at the single nanoparticle level. The nanoparticles were modified with neutravidin via epoxide–azide coupling chemistry, to which biotinylated antibodies targeting cell surface receptors were bound. The nanoparticle labels exhibited long-term stability in solutions with high salt concentrations without aggregation or silver etching. Labeled cells exhibited two orders of magnitude enhancement of the scattering intensity compared with unlabeled cells.

Production of biodiesel from sunflower oil using highly catalytic bimetallic gold–silver core–shell nanoparticle

Bimetallic Gold–silver core–shell nanoparticles (Au@Ag NPs) were synthesized at room temperature, where gold nanoparticles (AuNPs) served as seeds for continuous deposition of silver atoms on its surface. The core–shell structure was examined by UV–vis spectroscopy, transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) analysis. The catalytic activity of these nanoparticles toward biodiesel production from Sunflower oil through transesterification was studied. The confirmation for biofuel synthesis was performed using Fourier Transform Infra-Red (FTIR) spectroscopy. Fuel properties are determined by standard ASTM (American society for Testing and Materials) protocols. Our observations show that at certain catalyst concentration, temperature and reaction time, highest yield of biodiesel (86.9%) is attained. The fuel properties of the synthesized biofuel are at par with standard biofuel. Further, the catalyst showed sustained activity for 3 cycles of transesterification.

Gold nanodumbbell-seeded growth of silver nanobars and nanobipyramids

Gold nanodumbbells (NDs) are prepared by the reduction of gold ions in the presence of gold nanorods. Gold NDs are then employed for the synthesis of gold–silver core–shell nanoparticles (Au@Ag NPs). The quasi-ellipsoidal NPs could be found at room temperature, but Au@Ag bar and triangular bipyramid (TBP) NPs were obtained at 75°C. Our results show that the long ends of gold NDs are in the position of the bar center and closely paralleled the shorter edge of TBP. Mechanisms in the growth of silver on gold NDs are proposed for the formations of these Au@Ag NPs.

Enhanced Raman signals from switchable nanoparticle probes

We demonstrate here a DNA-based conformationally switchable nanodumbell structure that modulates the interparticle distance between two gold-silver core-shell nanoparticles to induce significant changes in the SERS signal.

Core–shell gold/silver nanoparticles: Synthesis and optical properties

Highly dispersed gold–silver core–shell nanoparticles were synthesized in a two-step process. The stabilizer-free gold core particles with an average diameter of ∼30nm were first precipitated by rapid reduction of HAuCl4 with l-ascorbic acid. Thin continuous silver shells of variable thickness were subsequently obtained by reducing controlled amounts of silver nitrate added in the gold sol. The plasmon band of gold gradually blue-shifted and a peak characteristic for silver eventually emerged as the amount of deposited silver increased. A strong and well-defined silver absorption band was recorded when the Ag content exceeded 60wt.%. It is shown that the concentration of Cl− ions in the gold precursor solution plays a critical role in the stability of the bi-metallic sol and the structure of the deposited silver shell.

Optical detection of NADH based on biocatalytic growth of Au–Ag core–shell nanoparticles

We have developed an optical assay for NADH (Dihydronicotinamide adenine dinucleotide) based on the catalytic growth of gold–silver core–shell nanoparticles (Au–Ag–CSNPs). The nanoparticles were immobilized on pretreated glass slide and are shown to catalyze the NADH-mediated reduction of Ag(I) ions in the presence of 1,4-benzoquinone and cetyltrimethyl ammonium ion. This leads to the formation of Au–Ag–CSNPs on the glass. The absorption peak of the Au–Ag–CSNPs at 415nm increases with the concentration of NADH in the solution used, and this can be measured by UV–vis photometry. High-resolution scanning electron microscopy analysis of the morphology of the surface of the Au–Ag–CSNPs before and after the catalytic reaction revealed a growth of their diameter. Under optimal conditions, NADH can be determined in the concentration range from 0.2 to 3.2mM, and the detection limit is 15.6μM. The sensor has good precision and good storage stability, simple in operation, and can be fabricated at low costs, which made it suitable for the determination of NADH in complex biological systems and in related degradation processes of contaminants.

Chemical stabilization of gold coated by silver core–shell nanoparticles via electron transfer

Silver nanoparticles are notoriously susceptible to oxidation, yet gold nanoparticles coated in silver exhibit a unique electronic interaction that occurs at the interface of the two metals, leading to enhanced stability properties for the silver shell. In order to probe the phenomenon, the stability of gold nanoparticles coated by silver was studied in the presence of various chloride-containing electrolytes. It was found that a critical silver shell thickness of approximately 1 nm exists that cannot be oxidatively etched from the particle surface: this is in contrast to the observation of complete oxidative etching for monometallic silver nanoparticles. The results are discussed in terms of particle composition, structure and morphology before and after exposing the particles to the electrolytes. Raman analysis of the reporter molecule 3-amino-1,2,4-triazole-5-thiol adsorbed on the particle surface illustrates the feasibility of using gold coated by silver nanoparticle probes in sensing applications that require the presence of high levels of salt. The results provide insight into the manipulation of the electronic and stability properties for gold- and silver-based nanoparticles.

Aerosol copper initiated core–shell nanoparticle synthesis and micropatterning

We report the development of copper–silver core–shell nanoparticles where the aerosol copper nanoparticles served as the seeds for the deposition of silver atoms on their surface. The copper particles were also electrostatically patterned on the substrate to fabricate silver micropatterns.

Sono and electrochemical synthesis and characterization of copper core–silver shell nanoparticles

Cu–Ag core–shell nanopowders have been prepared by ultrasound-assisted electrochemistry followed by a displacement reaction. The composition of the particles has been determined by X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX). The XRD patterns versus time displacement show that higher are the silver peaks intensities, weaker are the copper ones. That exhibits the progressive recovering of copper by silver. EDX results and quartz crystal microbalance results indicate that various reaction mechanisms are implied in this process. Transmission electron microscopy (TEM) points out variable nanometric diameter grain and some small agglomerates. Elemental mapping obtained by electron energy-loss spectroscopy (EELS) underlines the core–shell structure.

Synthesis of gold nanopeanuts by citrate reduction of gold chloride on gold–silver core–shell nanoparticles

A simple method of fabricating shape-tunable Au nanopeanuts from Au-Ag core-shell nanoparticles based on both galvanic replacement and reagent reduction is described.