Multilayer Nanoshells Research Articles

Tunable Fano resonance in symmetric multilayered gold nanoshells

We have studied the evolution of dipole-dipole all-plasmonic Fano resonances (FRs) in symmetric multilayered nanoshells as a function of their geometrical parameters. We demonstrate that symmetry breaking is not mandatory for controlling the Fano resonance in such multilayer structures. By carefully selecting the geometrical parameters, the position of the FR can be tuned between 600 and 950 nm and its intensity can be increased up to four fold with respect to the non-optimized structures. Generation of FRs in such symmetric nanostructures presents clear advantages over their asymmetric counterparts, as they are easier to fabricate and can be used in a wider range of technological applications.

Frequency-Dependent Polarization Properties of Local Electric Field in Gold–Dielectric Multi-Nanoshells

The polarization properties of the local electric field in the gold–dielectric–gold multilayer nanoshells are investigated by theoretical calculation based on the quasi-static approximation. The calculation results show that the complete polarized incident light does not only stimulate the same directional polarized local electric field. The polarized angle of the local field may changes from 0° to 90° as the wavelength and location are changed. The distributions of local field polarization are different in dielectric layer or gold shell and display different features in different plasmonic hybridization mode. As the incident wavelength is increased, the hot spot of polarizing angle moves monotonously in the middle dielectric shell, whereas moves nonmonotonously in the gold shell and surrounding environment. In the gold shell, the gap between hot spots of polarizing angle may occur at the resonance frequency. However, the hot spots of polarizing angle always occur at the resonance frequencies in the surrounding environment. These interesting results show that the single-molecule detection based on metal nanostructure induced surface-enhanced Raman scattering and surface enhanced fluorescence could be optimized by adjusting the incident light polarization and frequency.

Optimization of Three-Layered Au–Ag Bimetallic Nanoshells for Triple-Bands Surface Plasmon Resonance

Plasmonic light absorption properties of three-layered Au–Ag bimetallic nanoshells are investigated using the quasi-static electricity and plasmon hybridization theory. Comparing with Au-dielectric-Au and Ag-dielectric-Au multilayer nanoshells, Au-dielectric-Ag multilayer nanoshells are demonstrated more suitable for triple-bands surface plasmon resonance (SPR). Calculation results indicated that the triple plasmon resonance in Au-dielectric-Ag multilayer nanoshells could be optimized by choosing appropriate geometrical dimensions of the inner gold sphere and outer silver shell. The corresponding physical mechanism has also been illustrated by analyzing the surface charge distribution and intercoupling of the polarization fields from different metal–dielectric interfaces. This triple-bands SPR in the bimetallic multilayer nanostructure provides potential for multiplex biosensing based on SPR absorption, surface enhanced fluorescence, and surface enhanced Raman scattering (SERS).

Optical Extinction Properties of Perforated Gold-Silica-Gold Multilayer Nanoshells

Symmetry breaking in gold nanoshell (or multilayer nanoshells) can supply many interesting optical properties, which has been studied in gold nanostrucutres such as nanocup, nanoegg, and core offset gold-silica-gold multilayer nanoshells. In this work, the optical extinction properties of the perforated gold-silica-gold multilayer nanoshells are studied by the discrete dipole approximation method simulations and plasmon hybridization theory. The extinction spectra of these particles are sensitive to the orientation of the particle with respect to polarization of the light due to the symmetry breaking. Because of the coupling of the plasmon resonance modes between the inner gold sphere and the outer nanocup structure, the perforated gold-silica-gold nanoshell provides the additional plasmon resonance peak and an even greater spectral tunability comparing with the nanocup of similar dimensions. By changing the geometry of the particles, the extinction peaks of the particles can be easily tuned into the near-infrared region, which is favorable for biological applications. The local refractive index sensitivity of the particles is also investigated, and the multiple extinction peaks simultaneous shift is found as surrounding medium is altered. The perforated gold-silica-gold multilayer nanoshells may provide various applications ranging from angularly selective filters to biological sensors.

Third order harmonics generation in multilayer nanoshells

Third order harmonics generation has been investigated for multilayer nanoshell structure. Numerical calculations show that the nonlinear susceptibility of this structure depends on the parameters such as size and kind of structure, relaxation time and pump photon energy. The intensity and position of third order nonlinear susceptibility peaks depend on shell thicknesses; smaller thicknesses have peak susceptibility at shorter wavelength.

Polyelectrolyte multilayer nanoshells with hydrophobic nanodomains for delivery of Paclitaxel

Efficient and effective delivery of poorly water-soluble drug molecules, which constitute a large part of commercially available drugs, is a major challenge in the field of drug delivery. Several drugs including paclitaxel (PTX) which are used for cancer treatment are hydrophobic, exhibit poor aqueous solubility and need to be delivered using an appropriate carrier. In the present work, we engineered PTX-loaded polyelectrolyte films and microcapsules by pre-complexing PTX with chemically modified derivative of hyaluronic acid (alkylamino hydrazide) containing hydrophobic nanocavities, and subsequent assembly with either poly(l-lysine) (PLL) or quaternized chitosan (QCHI) as polycations. The PTX loading capacity of the films was found to be dependent on number of layers in the films as well as on the initial concentration of PTX pre-complexed to hydrophobic HA, with a loading capacity up to 5000-fold the initial PTX concentration. The films were stable in physiological medium and were degraded in the presence of hyaluronidase. The PTX-loaded microcapsules were found to decrease the viability and proliferation of MDA MB 231 breast cancer cells, while unloaded microcapsules did not impact cell viability. All together, our results highlight the potential of hyaluronan-based assemblies containing hydrophobic nanodomains for hydrophobic drug delivery.

Tunable Fano resonances in silver–silica–silver multilayer nanoshells

We study the plasmonic properties of silver–silica–silver multilayer nanoshells using finite-difference time-domain methods. Silver is a weakly dissipating metal and is able to support higher order resonances compared to strongly dissipating metals like gold. We show that Fano resonances occur even in symmetric cases. Symmetry breaking via the introduction of core offset further enhances these Fano resonance peaks and leads to the appearance of higher order resonances. The optical properties of the multilayer nanoshells are explained using the plasmon hybridization theory and the results are compared to similar multilayer nanoshells with gold core and outer shell.

Fluorescence characteristics of a molecule in the vicinity of a plasmonic nanomatryoska: Nonlocal optical effects

The fluorescence characteristics of a dipole molecule in the vicinity of a spherical multilayered metallic nanoshell (a plasmonic nanomatryoska) of ultra-small dimensions is studied via electrodynamic modeling, where we have computed the fluorescence decay rates, the shifts in emission frequency, and the overall fluorescence yields for molecular dipoles of both tangential and radial orientations. Our focus is on structures of ultra small dimensions in order to elucidate the possibly novel nonlocal optical effects in such a phenomenon. The results show that at very close distances between the molecule and the nanoshell, the nonlocal effects in general lead to smaller structure-induced effects with broadened and blue-shifted plasmonic resonances. These effects include overall smaller induced decay rates, smaller red-shifts in emission frequency, and somewhat larger fluorescence yields at low emission frequencies. Physical interpretation of our simulation results is provided.

The Resonance Scattering Quantum Yield with Modulated Structure of the Dielectric-Metal Multilayer Nanoshells

The Resonance Scattering Quantum Yield with Modulated Structure of the Dielectric-Metal Multilayer Nanoshells

Subradiant Plasmon Modes in Multilayer Metal–Dielectric Nanoshells

Subradiant plasmon modes play an important role in plasmon coupling, which can couple to the superradiant modes resulting in Fano resonances. In this study, we investigated the behaviors of the subradiant plasmons in multilayer metal–dielectric nanoshells using the generalized Mie theory. We showed that it is possible to get a pronounced Fano resonance in a single concentric nanoshell by controlling the size and geometry. The near-field coupling effects in multilayer nanoshell chains were studied by changing the alignment, particle number, and interparticle spacing. The local electric field and induced surface charge distributions were plotted to gain physical insight into the coupling mechanisms. The interactions between the particles result in a well-developed Fano resonance due to the broadening of bright plasmon modes. The subradiant plasmon modes remain robust and nearly uninfluenced by the near-field coupling and the surrounding medium. At the Fano resonance frequency, the largest field enhancement occurs in the silica layer, which is quite different from solid metal nanoparticle chains.

Interior Structural Tailoring of Cu2O Shell-in-Shell Nanostructures through Multistep Ostwald Ripening

We report a multistep Ostwald ripening approach through which the interior multilayer structures of a Cu2O shell-in-shell nanoparticle can be controllably tailored. Using this method, we can fine-control several important geometrical parameters of Cu2O multilayer nanoshells, such as the number of layers, the thickness of each shell, and the intershell spacing, to systematically fine-tune the synergistic optical properties of the particles over a broad spectral range in the visible and near-infrared regions. We have performed Mie scattering theory calculations to interpret the origin of the complex, multipeaked extinction spectral line shapes and geometry-dependent optical tunability of the Cu2O multilayer nanoshells.

The Plasmon Resonance of a Multilayered Gold Nanoshell and its Potential Bioapplications

The optical spectra and near-field enhancement of a multilayered gold nanoshell were theoretically studied in this paper to explore its potential biological applications. The mathematical model was developed within the framework of multipole expansion of a multilayered concentric sphere. Results show that compared with a conventional single-layered Au-SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanoshell, a multilayered Au-SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -Au nanoshell has an advantage of realizing the localized surface plasmon resonance at wavelength of 1300 nm or longer, which is believed to be more beneficial to ultrahigh resolution optical coherent imaging. With single-layered nanoshell, an extremely thin gold layer is required for resonance at long wavelength, and making such thin layer would be almost practically impossible within the current synthesis techniques.

Enhancement of light absorption of cadmium sulfide nanoparticle at specific wave band by plasmon resonance shifts

Cadmium sulfide (CdS) is a common photocatalyst used for photocatalytic processes. Only those photons with energy above or equal to 2.4 eV (corresponding to band gap of CdS) are absorbed and contribute to the photocatalytic behavior. In this paper, the concept of multilayer nanoshell plasmonic photocatalyst is introduced into photocatalysis for hydrogen production based on the water-splitting technique. The optical properties of novel multilayer nanoshells consisting of Ag, SiO 2 and CdS are investigated by means of plasmonics theory and plasmon hybridization model. The optical properties with structural parameters of Ag/SiO 2/CdS composite nanoparticles are studied by discrete dipole approximation (DDA) method. The results show that the absorption performance of this novel multilayer nanoshell is remarkably improved when localized surface plasmon resonance (LSPR) is excited on the surface of Ag nanoparticle exposed under UV–vis illumination. By adjusting the intermediate layer thickness, the resonance wavelength can be conveniently tuned to desired wavelength range. For a thinner intermediate layer, the resonance wavelength is red shifted. Parameter optimization gives rise to the optimal structure of outstanding absorption performance.

Quadratic electro-optic effects and electro-absorption process in multilayer nanoshells

The third-order nonlinear susceptibility is obtained as a function of wavelength for a multilayer nanoshell structure. Numerical calculations show that the nonlinear susceptibility of this structure depends on parameters such as the structure size, relaxation time and pump photon energy. The intensity and position of third-order nonlinear susceptibility peaks depend on shell thicknesses; smaller thicknesses have peak susceptibility at shorter wavelengths.

Computational Multiscattering of Spherical Multilayered Gold Nanoshells

A generalized computational methodology is developed and applied to study multiscattering phenomena associated with an aggregate of multilayered nanoshells under excitation of a plane wave. The development is based on a combination of the vector addition theorem for spherical wave functions and the efficient recursive procedure for multilayered nanoshells. Calculated results are compared well with spectral measurements for a Au@SiO2 nanodimer. They are also in qualitative agreement with laboratory observations. Resonance behavior of a Au@SiO2 nanoshell chain depends on the number of particles in the chain, the orientation of the chain, and the interparticle spacing. Strong localized field enhancement is observed in the gap between two adjacent particles, and intense Joule heating occurs in the portion of the metal shell where the field enhancement is weak. The coupled plasmonic resonance of a multilayered nanodimer is analyzed, and its application as a plasmon ruler is discussed.

Layer-by-Layer Assembly of TaO3 Nanosheet/Polycation Composite Nanostructures: Multilayer Film, Hollow Sphere, and Its Photocatalytic Activity for Hydrogen Evolution

Multilayer composite films comprising of TaO3 nanosheet crystallites and poly(diallyldimethylammonium chloride) (PDDA) were assembled via layer-by-layer sequential adsorption. Exposure of the resulting films to UV light promoted photocatalytic decomposition of PDDA in the nanosheet gallery to yield inorganic films. Novel hollow microspheres of Ta2O5 were fabricated by the deposition of a PDDA/TaO3 multilayer nanoshell on polystyrene (PS) beads and the subsequent removal of the PS core and PDDA layers via calcination. The hollow microspheres showed photocatalytic properties effective for hydrogen evolution from an aqueous methanol solution. The shape control into hollow microsphere greatly enhanced the photocatalytic activity. The results highlight the role of the surface area and crystallinity of the catalyst in photocatalytic activity.

Symmetry Breaking in Gold−Silica−Gold Multilayer Nanoshells

We present a computational study of the plasmonic properties of gold-silica-gold multilayer nanoshells with the core offset from the center. Symmetry breaking, due to the core offset, makes plasmon resonances that are dark in concentric geometries visible. Applying plasmon hybridization theory, we explain the origin of these resonances from the interactions of an admixture of both primitive and multipolar modes between the core and the shell. The interactions introduce a dipole moment into the higher order modes and significantly enhance their coupling efficiency to light. To elucidate the symmetry breaking effect, we link the geometrical asymmetry to the asymmetrical distribution of surface charges and demonstrate illustratively the diminishing multipolar characteristic and increasing dipolar characteristic of the higher order modes. The relative amplitudes of the modes are qualitatively related by visual examination of the dipolar component in the surface charge distributions. Using polarization-dependent surface charge plots, we illustrate two distinct mode configurations despite their spectral similarities. We further demonstrate a trend of increasing absorption relative to scattering as the resonant wavelength red shifts in response to a larger core offset.

Optical properties of gold-silica-gold multilayer nanoshells

The spectral and angular radiation properties of gold-silica-gold multilayer nanoshells are investigated using Mie theory for concentric multilayer spheres. The spectral tunability of multilayer nanoshells is explained and characterized by a plasmon hybridization model and a universal scaling principle. A thinner intermediate silica layer, scaled by particle size, red shifts the plasmon resonance. This shift is relatively insensitive to the overall particle size and follows the universal scaling principle with respect to the resonant wavelength of a conventional silica-gold core-shell nanoshell. The extra tunability provided by the inner core further shifts the extinction peak to longer wavelengths, which is difficult to achieve on conventional sub-100 nm nanoshells due to limitations in synthesizing ultrathin gold coatings. We found multilayer nanoshells to be more absorbing with a larger gold core, a thinner silica layer, and a thinner outer gold shell. Both scattering intensity and angular radiation pattern were found to differ from conventional nanoshells due to spectral modulation from the inner core. Multilayer nanoshells may provide more backscattering at wavelengths where silica-gold core-shell nanoshells predominantly forward scatter.

Engineering sub-100 nm multi-layer nanoshells

Nanoshells are a novel class of optically tunable nanoparticles that consist of alternatingdielectric and metal layers. They can potentially be used as contrast agents for multi-labelmolecular imaging, provided that the shell thicknesses are tuned to specific ratios.Sub-100 nm multi-layer nanoshells can potentially have improved tissue penetration,generate a strong surface plasmon resonance, and may exhibit absorption peaks inthe visible–near-infrared (NIR) spectrum. Herein we describe the synthesis andcharacterization of bilayered concentric nanoshells with an overall diameter of around 50 nmconsisting of a gold core, a tunable silica spacer layer and an outermost gold shell,which is approximately 16 times smaller than previously described multi-layerednanoparticles. The structured nanoshells were visualized by transmission electronmicroscopy (TEM) at each step of preparation. The absorption spectra of thegold–silica bilayered nanoshells are in good agreement with Mie’s prediction and theirresonance peak position is a function of the relative thickness of silica and gold layers.