Gold-silver Nanoshells Research Articles

Hollow Gold-Silver Nanoshells Coated with Ultrathin SiO2 Shells for Plasmon-Enhanced Photocatalytic Applications.

This article details the preparation of hollow gold-silver nanoshells (GS-NSs) coated with tunably thin silica shells for use in plasmon-enhanced photocatalytic applications. Hollow GS-NSs were synthesized via the galvanic replacement of silver nanoparticles. The localized surface plasmon resonance (LSPR) peaks of the GS-NSs were tuned over the range of visible light to near-infrared (NIR) wavelengths by adjusting the ratio of silver nanoparticles to gold salt solution to obtain three distinct types of GS-NSs with LSPR peaks centered near 500, 700, and 900 nm. Varying concentrations of (3-aminopropyl)trimethoxysilane and sodium silicate solution afforded silica shell coatings of controllable thicknesses on the GS-NS cores. For each type of GS-NS, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images verified our ability to grow thin silica shells having three different thicknesses of silica shell (~2, ~10, and ~15 nm) on the GS-NS cores. Additionally, energy-dispersive X-ray (EDX) spectra confirmed the successful coating of the GS-NSs with SiO2 shells having controlled thicknesses. Extinction spectra of the as-prepared nanoparticles indicated that the silica shell has a minimal effect on the LSPR peak of the gold-silver nanoshells.

Optically Tunable Tin Oxide-Coated Hollow Gold-Silver Nanorattles for Use in Solar-Driven Applications.

Core@shell metal nanoparticles have emerged as promising photocatalysts because of their strong and tunable plasmonic properties; however, marked improvements in photocatalytic efficiency are needed if these materials are to be widely used in practical applications. Accordingly, the design of new and functional light-responsive nanostructures remains a central focus of nanomaterial research. To this end, we report the synthesis of nanorattles comprising hollow gold–silver nanoshells encapsulated within vacuous tin oxide shells of adjustable thicknesses (∼10 and ∼30 nm for the two examples prepared in this initial report). These composite nanorattles exhibited broad tunable optical extinctions ranging from ultraviolet to near-infrared spectral regions (i.e., 300–745 nm). Zeta potential measurements showed a large negative surface charge of approximately −35 mV, which afforded colloidal stability to the nanorattles in aqueous solution. We also characterized the nanorattles structurally and compositionally using scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. Futhermore, finite-difference time-domain simulation and photoluminescence properties of the composited nanoparticles were investigated. Collectively, these studies indicate that our tin oxide-coated hollow gold–silver nanorattles are promising candidates for use in solar-driven applications.

Antimony- and Zinc-Doped Tin Oxide Shells Coated on Gold Nanoparticles and Gold–Silver Nanoshells Having Tunable Extinctions for Sensing and Photonic Applications

This paper reports the synthesis and study of doped metal oxides as the shell in core-shell nanoparticle architectures. Specifically, the manuscript describes the synthesis of gold nanoparticles (A...

Gold–silver nanoshells promote wound healing from drug-resistant bacteria infection and enable monitoring via surface-enhanced Raman scattering imaging

Chronic infections, caused by multidrug-resistant (MDR) bacteria, constitute a serious problem yet often underappreciated in clinical practice. The in situ monitoring of the bacteria-infected disease is also necessary to track and verify the therapeutic effect. Herein we present a facile approach to overcome the above challenges through a Raman tag 3,3′-diethylthiatricarbocyanine iodide (DTTC)-conjugated gold-silver nanoshells (AuAgNSs). With a strong responsive of the near-infrared laser due to surface plasmon resonance (SPR) from hybrid metallic nanoshell structure, AuAgNSs exhibits an efficient photothermal effect, and it simultaneously releases silver ions during laser irradiation to bacterial eradicate. Herein, two MDR bacteria strain, methicillin-resistant Staphylococcus aureus (MRSA) and extended-spectrum β-lactamase Escherichia coli, are chosen as models and studied both in vitro and in vivo. As a result, the AuAgNSs-DTTC substrates enable surface-enhanced Raman scattering imaging to provide a non-invasive and extremely high sensitive detection (down to 300 CFU mL−1 for MRSA) and prolonged tracking (at least 8 days) of residual bacteria. In a chronic MRSA-infected wound mouse model, the AuAgNSs gel-mediated photothermal therapy/silver-release leads to a synergistic would healing with negligible toxicity or collateral damage to vital organs. These results suggest that AuAgNSs-DTTC is a promising anti-bacterial tool for clinical translation.

Gold and silver quantification from gold-silver nanoshells in HaCaT cells

A method to determine total gold (Au) and/or silver (Ag) elemental concentrations from gold nanoparticles, Au-Ag nanoshells (NS) and silica coated Au-Ag nanoshells was developed, evaluated and validated. Samples were mineralized in a mixture of concentrated aqua regia and hydrofluoric acid at 65 °C for 4 h. Mineralized solutions were diluted and standard solutions were prepared in aqua regia 5%. ICP-MS analysis was performed with or without the use of a reaction cell (CRC). For the determination of elemental concentrations of nanopowders and test suspensions, the average recovery was 99 ± 2% and 101 ± 2% for gold and silver respectively. The repeatability was evaluated by the Relative Standard Deviation (RSD). The overall analytical RSD was ≤4% (n = 3) and the RSD associated to ICP-MS analysis was ≤2% (n = 10). The limits of detection were 0.005 and 0.002 μg(element) L−1 (analyzed solution), and the limits of quantitation 0.017 and 0.005 μg(element) L−1 (analyzed solution), for 197Au and 109Ag respectively. The Ag/Au mass ratios of the NS in the different samples considered were all equal to (0.93 ± 0.04). From this information, the average thickness of gold and silver layers in the nanoshells was deduced, being 7.5 ± 0.5 and 23 ± 3 nm respectively. Finally, the developed method was successfully applied to in vitro studies to evaluate NS cellular uptake in HaCaT keratinocyte cells confirming the method robustness toward biological medium. Experiments in cell culture medium gave coherent concentrations, 70–100% of uncoated or silica-coated NS being recovered, distributed between the culture medium and the cells (internalized). The analytical repeatability (over the whole procedure, or that of the ICP-MS analysis only) remains in the same order of magnitude as in test suspensions. Minimum concentrations less than or equal to 1 μg(element) g−1(suspension) were determined with the same accuracy.

Surface modification with zwitterionic cysteine betaine for nanoshell-assisted near-infrared plasmonic hyperthermia

Nanoparticles decorated with biocompatible coatings have received considerable attention in recent years for their potential biomedical applications. However, the desirable properties of nanoparticles for in vivo uses, such as colloidal stability, biodistribution, and pharmacokinetics, require further research. In this work, we report a bio-derived zwitterionic surface ligand, cysteine betaine (Cys-b) for the modification of hollow gold-silver nanoshells, giving rise to hyperthermia applications. Cys-b coatings on planar substrates and nanoshells were compared to conventional (11-mercaptoundecyl)tri(ethylene glycol) (OEG-thiol) to investigate their effects on the fouling resistance, colloidal stability, environmental tolerance, and photothermal properties. The results found that Cys-b and OEG-thiol coatings exhibited comparable antifouling properties against bacteria of gram-negative Pseudomonas aeruginosa (P. aeruginosa) and gram-positive Staphylococcus epidermidis (S. epidermidis), NIH-3T3 fibroblasts, and bovine serum albumin. However, when the modified nanoshells were suspended at a temperature of 50°C in aqueous 3M NaCl solutions, shifts in the extinction maximum of the OEG-capped nanoshells with time were observed, while the corresponding spectra of nanoshells capped with Cys-b generally remained unchanged. In addition, when the nanoshells were continuously exposed to NIR irradiation, the temperature of the solution containing nanoshells capped with Cys-b increased to a plateau of 54°C, while that of the OEG-capped nanoshells gradually decreased after reaching a peak temperature. Accordingly, the Cys-b nanoshells were conjugated with anti-HER2 antibodies for targeted delivery to HER2-positive MDA-MB-453 breast cancer cells for hyperthermia treatment. The results showed the selective delivery and effective photothermal cell ablation with the antibody-conjugated Cys-b nanoshells. Therefore, this work demonstrated the promise of bio-derived zwitterionic Cys-b as a stable and biocompatible surface coating for materials in nanomedicine.

Plasmonically Enhanced Photocatalytic Hydrogen Production from Water: The Critical Role of Tunable Surface Plasmon Resonance from Gold-Silver Nanoshells.

Gold-silver nanoshells (GS-NSs) having a tunable surface plasmon resonance (SPR) were employed to facilitate charge separation of photoexcited carriers in the photocalytic production of hydrogen from water. Zinc indium sulfide (ZnIn2S4; ZIS), a visible-light-active photocatalyst, where the band gap varies with the [Zn]/[In] ratio, was used as a model ZIS system (E(g) = 2.25 eV) to investigate the mechanisms of plasmonic enhancement associated with the nanoshells. Three types of GS-NS cores with intense absorptions centered roughly at 500, 700, and 900 nm were used as seeds for preparing GS-NS@ZIS core-shell structures via a microwave-assisted hydrothermal reaction, yielding core-shell particles with composite diameters of ∼200 nm. Notably, an interlayer of dielectric silica (SiO2) between the GS-NSs and the ZIS photocatalyst provided another parameter to enhance the production of hydrogen and to distinguish the charge-transfer mechanisms. In particular, the direct transfer of hot electrons from the GS-NSs to the ZIS photocatalyst was blocked by this layer. Of the 10 particle samples examined in this study, the greatest hydrogen gas evolution rate was observed for GS-NSs having a SiO2 interlayer thickness of ∼17 nm and an SPR absorption centered at ∼700 nm, yielding a rate 2.6 times higher than that of the ZIS without GS-NSs. The apparent quantum efficiencies for these core-shell particles were recorded and compared to the absorption spectra. Analyses of the charge-transfer mechanisms were evaluated and are discussed based on the experimental findings.

Ultrasmall Hollow Gold–Silver Nanoshells with Extinctions Strongly Red-Shifted to the Near-Infrared

Hollow gold-silver nanoshells having systematically varying sizes between 40 and 100 nm were prepared. These particles consist of a hollow spherical silver shell surrounded by a thin gold layer. By varying the volume of the gold stock solution added to suspensions of small silver-core templates, we tailored the hollow gold-silver nanoshells to possess strong tunable optical extinctions that range from the visible to the near-IR spectral regions, with extinctions routinely centered at ∼950 nm. The size and morphology of these core/shell nanoparticles were characterized by dynamic light scattering (DLS), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). Separately, X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) were used for measuring their elemental composition; UV-vis spectroscopy was used to evaluate their optical properties. Given their relatively small size compared to other nanoparticles that absorb strongly at near IR wavelengths, these easy-to-synthesize particles should find use in applications that require ultrasmall nanoparticles with extinctions comfortably beyond visible wavelengths (e.g., medicinal therapies, diagnostic imaging, nanofluidics, and display technologies).

Tunable near-infrared optical properties of three-layered metal nanoshells

The extinction spectra of a three-layered metal nanoshell, which consists of a particle with a dielectric core, a middle Ag (Au) layer, and an outer Au (Ag) shell, have been investigated by means of the Mie theory. With a decrease in the outer shell thickness or the middle layer thickness, the wavelengths of the localized surface plasmon resonance (LSPR) for SiO(2)-Ag-Au (SiO(2)-Au-Ag) nanoshells show distinct redshifts and the full widths at half maximum (FWHMs) for the dipole peaks in the extinction spectra decrease first and then increase. We have further investigated the influence of the embedding medium on the LSPRs for SiO(2)-Ag-Au and SiO(2)-Au-Ag nanoshells and found that the resonance wavelengths of the particles show redshift and the FWHM of the dipole peak increases with increasing the dielectric constant of the embedding medium. The calculated results indicate that the LSPR of the three-layered gold-silver nanoshells can be controlled to the near-infrared region by changing the geometry, which has practical biomedical application.