Gold Silver Core Shell Research Articles

Enhancement in Organic Photovoltaics Controlled by the Interplay between Charge-Transfer Excitons and Surface Plasmons.

In this work, we investigate plasmonic enhancement in poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester organic photovoltaics (OPVs) by integrating shape- and size-controlled bimetallic gold core–silver shell nanocrystals (Au–Ag NCs) into the poly(3,4-ethylenedioxythiophene):polystyrene sulfonate hole-transport layer. We observed that the best-performing Au–Ag NC-incorporated OPVs improved the power conversion efficiency by 9% via a broadband increase in photocurrent throughout the visible spectrum. Our experimental and computational results suggest that the observed photocurrent enhancement in plasmonic OPVs originates from both enhanced absorption and improved exciton dissociation and charge collection. This is particularly achieved by placing metal NCs near the interface of the active layer and hole-transport layer. The impedance spectroscopy results suggest that Au–Ag NCs reduce recombination and also increase the internal exciton to carrier efficiency by driving the dissociation of bound charge-transfer states to free carriers.

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.

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.

Green synthesis of Au@Ag nanostructures through a seed-mediated method and their application in SERS

Abstract A facile bottom-up “green” synthetic route is reported by using epigallocatechin gallate (EGCG) extract from tea leaves as a reducing and stabilizing agent in aqueous solution to produce silver nanostructures through a seed-mediated method at room temperature. The obtained gold core silver shell nanostructures (Au@Ag), whose sizes can be tuned through adjusting the amount of seeds, present polygonal morphologies. Meanwhile, the formation mechanism of Au@Ag nanoparticle has been investigated, in which Au-seeds act as nucleation sites for the formation of silver nanoparticles. The as-prepared Au@Ag nanostructure deposited on the glass plate can become the substrate of surface-enhanced Raman scattering (SERS), which has the obvious SERS effect when rhodamine 6 G (R6G) is used as the probe molecular. The above results indicate that the more irregular the shape of Au@Ag nanostructure becomes and the larger the size of nanoparticle gets, the stronger the SERS signal is.

Bull serum albumin coated Au@Agnanorods as SERS probes for ultrasensitive osteosarcoma cell detection

Surface-Enhanced Raman scattering (SERS) has been widely used for imaging and sensing. However, limited reports are currently available on SERS-based cancer cell targeting strategy due to the challenge of synthesizing highly sensitive, reproducible and biocompatible SERS probe. Herein, we developed novel SERS probes, based on BSA (Bull Serum Albumin) coated gold–silver core–shell nanorods modified with Raman reporter 5,5-dithiobis 2-nitrobenzoic acid (DTNB) (Au@AgNRs@BSA@Anti-MICA), for in vitro cancer cell detection. Our results demonstrate that the SERS probe is very robust for cancer cell ultrasensitive detection with good biocompatibility and strong SERS signal.

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).

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.

A novel and greener approach for shape controlled synthesis of gold and gold–silver core shell nanostructure and their application in optical coatings

Green and facile synthetic methods have gained marvellous fame for the production of polyhedral, anisotropic and spherical gold, and gold–silver bimetallic nanostructures. The useful pivotal characteristics of a green procedure are the usage of environment benign solvent medium, reducing and stabilising agents, and shorter reaction time. We describe here a novel, and greener method for the production of gold and gold–silver core shell nanostructures using aqueous fish scales extract of the Labeo rohita. The effect of various reaction parameters, such as temperature and concentration for the synthesis of the nanostructures were studied. Results indicated that triangular and decahedron gold nanostructures were formed at a lower temperature (40°C) and concentration (10%). While, icosahedral and spherical gold nanostructures were produced at a comparatively higher temperature (100°C) and concentration (40%). The study also revealed that the core–shell bimetallic nanostructures with different morphologies (spherical and oval-shape) were formed at different ratios of chloroaurate and silver nitrate solution. Thus, the present study indicated a simple shape controlled synthesis of gold and gold silver core–shell nanostructures. The synthesised gold nanotriangles were coated over the glass substrate and found to be highly efficient in absorbing infra-red radiations for potential architectural applications. Therefore, the study demonstrated the facile usage of gold nanotriangles for optical coatings. The present strategy depicted the dual functional ability of the fish scale extract as reducing and stabilising agents. This strategy also eliminates the usage of hazardous chemicals, toxic solvents and harsh reducing and stabilizing agents.

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...

Ultra-strong surface plasmon amplification characteristic of a spaser based on gold–silver core–shell nanorods

We proposed an efficient spaser based on gold–silver core–shell nanorods (NRs) encapsulated by an outer silica shell doped with a gain medium. The optical characteristics of the spaser were numerically simulated based on the finite element method (FEM). The results showed that the localized surface plasmon resonance (LSPR) amplification characteristics of the spaser strongly depend on the thickness of silver shell, the aspect ratio of the inner gold NRs, and the polarization direction of the incident light. And, the maximum absolute value of optical cross-section of the spaser can reach 21,824μm2, which is about 1115, 523, and 18 times higher than that of spasers based on the gold NRs, the silver NRs, and the silver–gold core–shell NRs, respectively. The ultra-strong surface plasmon amplification characteristics of the spaser have potential applications in optical information storage, high sensitivity biochemical sensing, and medical engineering.

Local Plasmonic Studies on Individual Core–Shell Gold–Silver and Pure Gold Nano-Bipyramids

Bimetallic systems present new opportunities to tailor the optical properties of nanoparticles. Morphology, structural, and optical properties of gold and of gold–silver nanoparticles have been studied by three-dimensional (3D) scanning transmission electron microscopy (STEM), STEM imaging, and monochromated subnanometer electron beams. The 3D morphology of these nanoparticles consists of bipyramidal prisms with well-defined facets. Furthermore, in the case of the core–shell nanoparticles, from these tomographical studies, we have determined the silver (shell) distribution and their atomic arrangement. Multipolar localized surface plasmon resonances (LSPR) have been studied, at subnanometer level and at high-energy resolution, as a function of their shape, their size (aspect ratio), and the surrounding environment. These results have been interpreted in the framework of the discrete dipole approximation (DDA) simulations. The effect of the silver outer-shell has been elucidated. We observed a significant damping of plasmon excitations due to the difference of dielectric function of these two metals. In addition, we have shown that the combination of the tomographical and plasmonic (experiments and simulations) studies with such high spatial resolution constitutes a very powerful and fundamental tool for understanding and optimizing the photonics properties of nanomaterials.

Plasmonic nanoparticle clusters with tunable plasmonic resonances in the visible spectral region

The seeded growth of poly(ethylene imine) – gold nanoparticle clusters enables the formation of particle assemblies with tunable optical properties. Clusters with increasing particle sizes, filling factors and assemblies consisting of PEI–gold–silver core shell particles can be synthesized in this way. Profound structural characterization is carried out via TEM imaging and FIB milling which allows visualizing the cross-section of the clusters. Determination of the optical properties was performed via UV-Vis spectroscopy and spectral dark field microscopy of individual particles. Additionally, numerical calculations were carried out based on the Mie theory. The results are in good agreement with the experimental findings and reveal the contribution of different multipoles to the spectra which cannot be resolved by UV-Vis spectroscopy in solution. The isotropic nature and adjustable properties of these clusters could render them versatile building blocks for metamaterials.

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.

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 ...

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.

Self‐Assembly of Au@Ag Nanorods Mediated by Gemini Surfactants for Highly Efficient SERS‐Active Supercrystals

The fabrication of supercrystals of standing core–shell gold–silver nanorods stabilized by gemini surfactants provides SERS substrates with high optical activity, large homogenous sensing areas, and the potential to maximize the SERS signal with respect to their gold nanorod supercrystal counterparts.

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.

Nonlinear Dependences of Optical Properties of Spherical Core–Shell Silver–Gold and Gold–Silver Nanoparticles on Their Parameters

Modeling of nonlinear optical properties of spherical core–shell gold–silver and silver–gold nanoparticles (NPs) placed in water was carried out on the base of extended Mie theory. Efficiency cross sections of absorption σ abs, scattering σ sca, and extinction σ ext of radiation with wavelengths λ = 400 and 532 nm for core–shell NPs with constant core radii r 00 = 5, 10, 20, and 40 nm and in the range of relative radii r 1/r 00 = 1–8 were calculated (r 1 is the radius of shell). Dependences of optical properties of gold–silver and silver–gold NPs on increasing of core radius r 0 in the range 0 − r 1 under condition r 1 = const and increasing of r 0 under r 1 − r 0 = const were investigated. Results show the nonlinear behavior of optical properties of core–shell gold–silver and silver–gold NPs on radiation wavelengths (optical indexes of metals), different core and shell radii, and their correlation, on relative NP radii r 1/r 00. An increase and decrease of absorption, scattering, and extinction efficiency cross sections of core–shell NPs with changing of wavelengths, core and shell radii, and relative NP radii r 1/r 00 are established. These dependences can be used for experimental investigation of the interesting first stages of shell formation on core and optical determination of core–shell NP parameters.