Metal Nanoshells Research Articles

Flexible thin-film black gold membranes with ultrabroadband plasmonic nanofocusing for efficient solar vapour generation.

Solar steam generation has been achieved by surface plasmon heating with metallic nanoshells or nanoparticles, which have inherently narrow absorption bandwidth. For efficient light-to-heat conversion from a wider solar spectrum, we employ adiabatic plasmonic nanofocusing to attain both polarization-independent ultrabroadband light absorption and high plasmon dissipation loss. Here we demonstrate large area, flexible thin-film black gold membranes, which have multiscale structures of varying metallic nanoscale gaps (0–200 nm) as well as microscale funnel structures. The adiabatic nanofocusing of self-aggregated metallic nanowire bundle arrays produces average absorption of 91% at 400–2,500 nm and the microscale funnel structures lead to average reflection of 7% at 2.5–17 μm. This membrane allows heat localization within the few micrometre-thick layer and continuous water provision through micropores. We efficiently generate water vapour with solar thermal conversion efficiency up to 57% at 20 kW m−2. This new structure has a variety of applications in solar energy harvesting, thermoplasmonics and related technologies.

Analysis of Localized Surface Plasmon Resonance in Ag/ITO/CdS/SiO2 Multilayered Nanostructured Composite

Multilayered nanoshells have attracted much attention due to their unique optical, electronic and magnetic properties. In this work, numerical calculation using discrete dipole approximation (DDA) is conducted to investigate the quad-layered metal nanoshell consisting of a particle with a dielectric silica (SiO2) core, inner cadium sulfide (CdS) shell, middle indium tin oxide (ITO) shell and outer metal silver (Ag) shell. The phenomenon is interpreted by plasmon hybridization theory and the Ag–ITO–CdS–SiO2 multilayered nanoshells are studied by extinction spectra of localized surface plasmon resonance. The variation in the spectrum peak with nanoparticle thickness and refractive index of the surrounding medium is derived. The electric field enhancement contour around the nanoparticles under illumination is analyzed at the plasmon resonance wavelength. The [Formula: see text], [Formula: see text], and [Formula: see text] modes red-shift with the refractive index of the surrounding medium and increase in the layer thickness causes either blue-shift or red-shift as shown by the extinction spectra. The mechanism of the red-shift or blue-shift is discussed. The [Formula: see text] mode blue-shifts and furthermore, the [Formula: see text] and [Formula: see text] modes of the Ag coated multilayered nanostructure are noticeable by comparing the extinction efficiency spectra of the Au–ITO–CdS–SiO2 and Ag–ITO–CdS–SiO2 multilayered nanoshells.

Application of Nanotechnology in Biomedicine: A Major Focus on Cancer Therapy <sup></sup>

Most of mortality worldwide occurs because of cancer diseases. Nanostructures are the new compounds that have become one of the most important technologies for using in different fields over the past two years especially in medicine. In between, nanotechnology has the potential to cancer detection and therapy. This study is a review of prospects in applications of nano-materials for cancer detection and treatment. We have summarized the nano-materials (metal nanospheres, nanorods, nanoshells and nanotubes) in medical applications targeting cancer. We also discuss advances in established nanoparticle technologies such as liposomes, polymer micelles, and functionalization about tumor targeting, controlled release and drug delivery. This paper will discuss the therapeutic applications of different nano-materials with a major focus on their applications for the treatment of cancer. Briefly, the toxicity of conventional nanostructures was also mentioned in this paper.

The effect of surface plasmon resonance on optical response in dielectric (core)–metal (shell) nanoparticles

In this work, we present the effect of refractive index of an embedding medium, core and shell having various sizes of metallic nanoshells on the surface plasmon resonance (SPR) properties in the spherical dielectric–metal core–shell nanoparticles based on the quasistatic approaches and Mie theory. For the metallic nanoshell with dimensions comparable to the wavelength of light, the quasistatic approximation shows good agreement with the Mie theory results. However, for large nanoparticles the quasistatic approximation is not appropriate and Mie theory illustrates SPR due to dipole and quadrupole in extinction cross-section. The typical cross-section calculations show two peaks that related to inner and outer surfaces. The dimensional dependence of optical constant in the Drude model leads to a decrease in plasma absorption in metal core–shell. By increasing the shell radius and therefore increasing the metal content the SPR at the outer surface shifts to higher energy and the weaker peak (at inner surface) shifts to lower energy. Also, depending on the metal shell materials SPR occurs in different energy regions and therefore can be tuned the SP frequency at higher energy by changing the shell materials. In addition, SPR frequency is sensitive to variation in refractive index of the environment of core-shell.

The enhancement of local electric field and farfield optical response of nanometallic shells

The optical response of various geometrical metallic nanoshell with silica are investigated by CST Microwave Studio® simulation. Farfield optical properties such as extinction cross section and enhancement of electric field on different geometrical surface are presented. The positions of plasmon absorptions near shorter and longer wavelength are also altered as changing the dimension parameters. Distorted irregular shapes NPs enormously enhance electric field as compared to regular NPs. Some particular simulation result is also compared to previously published work done by the method of Finite Difference Time Domain (FDTD) and Mie Theory. Assembles of NPs with different geometry size and shape are helpful in modeling multiple detected nano-antenna within optical frequency range.

Self-assembled Monolayer Mediated Surface Environment Modification of Poly(vinylpyrrolidone)-Coated Hollow Au-Ag Nanoshells for Enhanced Loading of Hydrophobic Drug and Efficient Multimodal Therapy.

Hollow Au-Ag bimetallic nanoshell possessing hydrophobic interior space and hydrophilic exterior surface was prepared and its application as a chemo-thermo-gene therapeutic agent based on its high payload of multiple drugs having different water solubility was demonstrated. The multifunctional drug delivery system is based on the hydrophobic interior created by the self-assembled monolayer (SAM) of hexanethiol onto the inner surface of the hollow metallic nanoshells whereas the outer surface was mostly coated by hydrophilic biocompatible polymer. The nanoshells having surface environment modified by hexanethiol SAMs provided high capacity both for hydrophilic DNAzyme (Dz) to induce gene silencing and for hydrophobic SN38 (7-ethyl-10-hydroxycamptothecin), anticancer drug. The release of the loaded Dz and SN38 was independently triggered by an acidic environment and by photothermal temperature elevation upon irradiation, respectively. The chemo-thermo-gene multitherapy based on the present nanoshells having modified surface environment showed high efficacy in quantitative cell-based assays using Huh7 human liver cell containing hepatitis C viral NS3 gene replicon RNA.

Effect of interaction retardation on the frequency of collective oscillations of electrons in metallic nanoparticles

The results of calculations of frequency of collective oscillations of electrons in metallic nanoshells are presented. The influence of interaction retardation is taken into account by the Rayleigh method. It is shown that the retardation results in a considerable decrease of the oscillation frequency, which, in its turn, reduces the radiation width of the spectrum. As a result, the spectral sensitivity of nanoshells is increasing.

Antiboding and bonding lasing modes with low gain threshold in nonlocal metallic nanoshell.

Based on a full-wave nonlocal Mie theory, we establish the spaser generation condition for compact plasmonic nanolasers in the long-wavelength limit for dielectric-metal core-shell nanoparticles. We found that there exist two lasing states arising from the hybridized antibonding and bonding modes for this coated nanolaser. By varying the surrounding medium and the gain materials, we can achieve low gain threshold for each mode with flexible radii ratios on the purpose of realistic easy fabrication. Numerical results show that nonlocal effects have different influences on the required gain threshold and gain refractive index of these two lasing modes, which may be of great importance in the design of such kind of ultrasmall nanoparticle lasers.

Hybrid plasmonic-photonic mode in a subwavelength fiber for enhanced single-nanoparticle detection

We study a hybrid mode in a composite system consisting of a localized metal nanosphere on a subwavelength fiber. It is found that the hybrid mode resulting from coupling of the fiber propagating mode and the plasmonic resonance is promising for strongly enhanced interaction between light and matter. We then propose a single-nanoparticle detection scheme by monitoring the nanofiber transmission change induced by the plasmonic-enhanced target scattering. The detection limit can be as low as 18 nm in target diameter, showing great potential for sensing single viruses or biomolecules. In the hybrid system, the resonant wavelength is tunable from visible to near-infrared spectral range by employing a metal nanoshell instead of the nanosphere, while the low detection limit of a few tens of nanometers can still remain.

A systematic growth of Gold nanoseeds on Silica for Silica@Gold core-shell nanoparticles and investigation of optical properties

Metal nanoshells consists of a dielectric core surrounded by a thin noble metal shell, possess unique optical properties, which render nanoshells attractive for use in different technologies. This paper reports a facile method for growth of small gold nanoparticles on the functionalized surface of larger silica nanoparticles. Mono-dispersed silica particles and gold nanoparticles were prepared by the chemical reduction method. The size of the shell nanoseeds could be altered by repeating the stage of reducing HAuCl4 on Au/APTES/silica particles, and the time for which they react. The nanocore-shell particles prepared were studied using transmission electron microscopy (TEM), UV–vis spectroscopy, Fourier transform infrared spectroscopy (FTIR) and PL spectrophotometer. The TEM images indicated that by growing gold nanoseeds over the silica cores a red shift in the maximum absorbance of UV-Visible spectroscopy is observed. Furthermore, a remarkable intensification happens in the PL spectra of silica@Au NPs in comparison with that of bare silica NPs. But, the existence of gold nanoseeds on the silica particles surfaces does not change the PL spectra peaks of these nanoparticles.

Optical and thermal radiative properties of plasmonic nanofluids containing core–shell composite nanoparticles for efficient photothermal conversion

Nanofluid has been proposed for use in direct absorption solar collector because of its unique thermal and optical radiative properties. The improvement of solar absorption efficiency was shown to be significantly influenced by the particle material, size, shape, volume fraction, etc. However, it was rare for simultaneously investigating the thermal and optical properties, especially the spectral ones that are critical for efficient photothermal application. Nonmetallic nanoparticles with metallic nanoshells can improve the spectral solar absorption efficiency since the effect of localized surface plasmon resonance (LSPR) exists at the surfaces of these core–shell composite nanoparticles. In this paper, the effect of LSPR at the surfaces of some typical composite nanoparticles (with Si or SiC core and Au, Ag, Cu or Al shell) on the optical and thermal radiative properties of water-based plasmonic nanofluids is numerically investigated by varying the particle radius ratio, outer radius and type of material of the composite nanoparticles in the dependent scattering regime through setting the volume fraction or particle distance. The scattering, absorption or extinction coefficient for these nanoparticles are calculated using the Mie scattering theory and the Rayleigh scattering approximation. The order of magnitude of near field interactions between the nanoparticles is demonstrated by two parallel nanoparticle arrays, based on the near field radiation heat flux between two nanoparticles using the fluctuation electrodynamics. The contributions of the optical absorption and thermal radiation in the near field are compared with the effective thermal conductivity of the nanofluids. The results show that the structure itself can simultaneously influence the average and the near field radiative properties of the composite nanoparticles and thus the plasmonic nanofluids. These coupling effects can be efficiently utilized for tuning the radiative properties of plasmonic nanofluids used in photothermal application.

Modulated retroreflector based on metallic nanoshells for applications in the visible band

In our research, we have theoretically studied a device that can serve as a modulating retroreflector (MRR) for applications in the visible spectrum. The device is comprised of a nanocomposite of a ferroelectric thin-film embedded with noble metal nanoshells. In comparison to the nanospheres, the nanoshells provide more flexibility in the design of the device. This MRR can be used in asymmetric communication links as an optical transceiver for mobile devices. The main conclusion from our study is that a nanocomposite-based MRR can save power, complexity, dimensions, and weight in comparison to standard communication links. This fact is very important for mobile platforms.

Light trapping characteristics of metal nanoshells deposited on photovoltaic silicon films

Light trapping characteristics of Ag nanoshells deposited on photovoltaic silicon films were studied theoretically using finite difference time domain (FDTD) method. The light absorption changes in Si films are found dependent on the localized surface plasmon resonance (LSP) including scattering, absorption and their respective portions, which can be tuned by varying the size of the metal nanoshells. Predominant scattering over absorption is demonstrated to be a prerequisite for the absorption enhancement. Metal absorption loss at LSP cavity mode resonance is responsible for the light absorption suppression. It is also found that the thickness of the active layer, which has effect on the LSP interference-induced field, influences light trapping characteristics of the Ag nanoshells.

Резонансне підсилення інтенсивності збудження молекули в спектрі непружного розсіяння електронів завдяки взаємодії з плазмонами металевої нанооболонки

A quantum-mechanical model to calculate the electron energy-loss spectra (EELS) for the system of a closely located metallic nanoshell and a molecule has been developed. At the resonance between the molecular excitation and plasmon modes in the nanoshell, which can be provided by a proper choice of the ratio of the inner and outer nanoshell radii, the cross-section of inelastic electron scattering at the molecular excitation energy is shown to grow significantly, because the molecular transition borrows the oscillator strength from a plasmon. The enhancement of the inelastic electron scattering by the molecule makes it possible to observe molecular transitions with an electron microscope. The dependences of the EEL spectra on the relative arrangement of the molecule and the nanoshell, the ratio between the inner and outer nanoshell radii, and the scattering angle are plotted and analyzed.

Dynamics of plasmonic field polarization induced by quantum coherence in quantum dot-metallic nanoshell structures.

When a hybrid system consisting of a semiconductor quantum dot and a metallic nanoparticle interacts with a laser field, the plasmonic field of the metallic nanoparticle can be normalized by the quantum coherence generated in the quantum dot. In this Letter, we study the states of polarization of such a coherent-plasmonic field and demonstrate how these states can reveal unique aspects of the collective molecular properties of the hybrid system formed via coherent exciton-plasmon coupling. We show that transition between the molecular states of this system can lead to ultrafast polarization dynamics, including sudden reversal of the sense of variations of the plasmonic field and formation of circular and elliptical polarization.

Synergistic effect of surface plasmonic particles in PbS/TiO2 heterojunction solar cells

Core–shell particles composed of a dielectric core and a metallic nanoshell exhibit tunable surface plasmons that may be exploited to enhance the light absorption capability of photoactive materials. This work uses both experimental and theoretical methods to elucidate the mechanism by which SiO2@Au@SiO2 (SGS) core–shell–shell particles improve the light harvesting efficiency of PbS–TiO2 heterojunction solar cells. The enhanced light absorption by PbS nanoparticles depends on their location in the device and their impact on device morphology. This study demonstrates that SGSs can promote the light harvesting of thin film solar cells in two ways. First, the localized surface plasmon resonance of the SGSs increases light scattering and the local electromagnetic field at the PbS–SGS interface. Second, placing SGSs between the PbS and TiO2 layers, forms nanodomes on top Au electrode and gives rise to additional light scattering that enhances the light harvesting efficiency. By combining these effects the short circuit current density and the energy conversion efficiency are increased by 29% and 24% respectively compared to a cell without SGSs.

Localized Surface Plasmon Resonance and Refractive Index Sensitivity of Metal–Dielectric–Metal Multilayered Nanostructures

The localized surface plasmon resonances of multilayered nanostructures are studied using finite difference time domain simulations and plasmon hybridization method. Concentric metal–dielectric–metal (MDM) structure with metal core and nanoshell separated by a thin dielectric layer exhibits a strong coupling between the core and nanoshell plasmon resonance modes. The coupled resonance mode wavelengths show dependence on the dielectric layer thickness and composition of core and outer layer metal. The aluminum-based MDM structures show lower plasmon wavelength compared with Ag- and Au-based MDM nanostructures. The calculated refractive index sensitivity (RIS) factor is in the order Ag–Air–Ag>Au–Air–Au>Al–Air–Al for monometallic multilayered nanostructures. Bimetallic multilayered nanostructures support strong and tunable plasmon resonance wavelengths as well as high RIS factor of 510 nm/refractive index unit (RIU) and 470 nm/RIU for Al–Air–Au and Ag-Air-Au, respectively. The MDM structures not only exhibit higher index sensitivity but also cover a wide ultraviolet–near-infrared wavelengths, making these structures very promising for index sensing, biomolecule sensing, and surface-enhanced Raman spectroscopy.

Plasmonics properties of trimetallic Al@Al2O3@Ag@Au and Al@Al2O3@AuAg nanostructures

Bimetallic and trimetallic nanoparticles have attracted significant attention in recent times due to their enhanced electrochemical and catalytic properties compared to monometallic nanoparticles. The numerical calculations using Mie theory has been carried out for three-layered metal nanoshell dielectric–metal–metal (DMM) system consisting of a particle with a dielectric core (Al@Al2O3), a middle metal Ag (Au) layer and an outer metal Au (Ag) shell. The results have been interpreted using plasmon hybridization theory. We have also prepared Al@Al2O3@Ag@Au and Al@Al2O3@AgAu triple-layered core–shell or alloy nanostructure by two-step laser ablation method and compared with calculated results. The synthesis involves temporal separations of Al, Ag, and Au deposition for step-by-step formation of triple-layered core–shell structure. To form Al@Ag nanoparticles, we ablated silver for 40 min in aluminium nanoparticle colloidal solution. As aluminium oxidizes easily in water to form alumina, the resulting structure is core–shell Al@Al2O3. The Al@Al2O3 particle acts as a seed for the incoming energetic silver particles for multilayered Al@Al2O3@Ag nanoparticles is formed. The silver target was then replaced by gold target and ablation was carried out for different ablation time using different laser energy for generation of Al@Al2O3@Ag@Au core–shell or Al@Al2O3@AgAu alloy. The formation of core–shell and alloy nanostructure was confirmed by UV–visible spectroscopy. The absorption spectra show shift in plasmon resonance peak of silver to gold in the range 400–520 nm with increasing ablation time suggesting formation of Ag–Au alloy in the presence of alumina particles in the solution.

Plasmonic-enhanced two-photon fluorescence with single gold nanoshell

Single gold nanoshell with mutilpolar plasmon resonances is proposed to enhance two-photon fluorescence efficiently. The single emitter single nanoshell configuration is studied systematically by employing the finite-difference time-domain method. The emitter located inside or outside the nanoshell at various positions leads to a significantly different enhancement effect. The fluorescent emitter placed outside the nanoshell can achieve large fluorescence intensity given that both the position and orientation of the emission dipole are optimally controlled. In contrast, for the case of the emitter placed inside the nanoshell, it can experience substantial two-photon fluorescence enhancement without strict requirements upon the position and dipole orientations. Metallic nanoshell encapsulating many fluorescent emitters should be a promising nanocomposite configuration for bright two-photon fluorescence label. The results provide a comprehensive understanding about the plasmonic-enhanced two-photon fluorescence behaviors, and the nanocomposite configuration has great potential for optical detecting, imaging and sensing in biological applications.

Shedding Light on the Growth of Gold Nanoshells

Nanostructured particles containing noble metals can have highly tunable localized surface plasmon resonances and are therefore of particular interest for numerous applications. Nanoshells comprising a dielectric core and gold or silver shell are a widely researched systems because of the strong dependence of their optical properties on the ratio of core diameter to shell thickness. Although seeded-growth procedures have been developed to produce these particles, the many reported studies show significant variation in the nanoshell morphologies and hence optical properties. In order to establish processes that reproducibly synthesize nanoshells with high optical quality, it is necessary to develop techniques that monitor changes at the core particle surface during shell growth. For that purpose, we have carried out in situ nonlinear second-harmonic scattering (SHS) and linear vis-NIR extinction spectroscopy simultaneously during the seeded growth of gold nanoshells on silica core particles. Our SHS measurements show a striking variation in the nonlinear optical properties of the growing gold nanoshells. In comparison with linear optical measurements and with scanning electron microscopy (SEM) images made of gold nanoshells produced with varying shell completenesses, the SHS signal was observed to reach a peak intensity at a stage prior to shell closure. We attribute this high sensitivity of the SHS signal to the incomplete nanoshell surface morphology to the generation and subsequent degeneration of regions of electric field enhancement at gaps between isolated gold islands, which grow and coalesce. This conclusion is corroborated by finite-difference time-domain simulations of incomplete nanoshells. We suggest that the in situ analytical approach demonstrated here offers significant promise for future activities regarding the in-process optimization of the morphology and optical properties of metal nanoshells and other nanostructured plasmonic particles.