Metal Nanoshells Research Articles

Topological magnetoelectric effect as probed by nanoshell plasmonic modes

Axion electrodynamics is applied to study the response of a plasmonic nanoshell with a core made of topological insulator (TI) materials. The electric polarizability of such a system is calculated in the long wavelength limit via the introduction of two scalar potentials satisfying the various appropriate boundary conditions. Our focus is on the topological magneto-electric effect (TME) as manifested in the coupled plasmonic resonances of the nanoshell. It is found that for a TI with broken time-reversal symmetry, such TME will lead to observable red-shifts in the coupled plasmonic modes, with more significant manifestation of such shifts for the bonding modes of a metallic nanoshell. It is speculated that such universal red-shift could be a manifestation of the fundamental dual symmetry as generalized for axion electrodynamics.

Refractive Index Monitoring Technique Using a Smartphone Based on the Metal Nanoshell Array Sensing Method

A novel surface plasmon resonance (SPR) sensor system using a smartphone based on the metal nanoshell array sensing method is proposed and developed. The micro-flow injection method was used to prepare two-dimensional colloidal microsphere template, the metal nanoshell array was fabricated by combining the microsphere template and the magnetron sputtering technology. A smartphone and a diffraction grating are employed as interrogation system, in which a fiber with a 45° polished tip connect the flashlight and the camera on the smartphone. The diffraction grating spreads the transmission spectrum over the camera's pixels to allow for repeatable measurements of wavelength shifts of the sensor. The reflection intensity of sensor can be measured by smartphone and the surrounding refractive index is monitored by the shift of the reflection spectrum. The experimental results show that the sensitivity of the SPR refractive index sensor based on the metal nanoshell array is about 927 nm/RIU for a refractive index (RI) range from 1.352 to 1.363, and the quality factor of that is about 18.5. The results show that this technique can provide a low-cost, portable and intelligent diagnostic platform for the measurement of the SPR refractive index sensor.

Enhanced energy localization in electromagnetically thick metallic mesoshells

While subwavelength dielectric structures enclosed by a thin metallic nanoshell have found a wide range of applications, their wavelength-scale counterparts have not been addressed. Conventionally, a dielectric enclosed by a thick metallic shell is considered isolated as the fields attenuate to a negligible value. Here, we show that, due to the Mie resonances of the wavelength-scale dielectric core, the energy density in the core can be enhanced by six orders of magnitude as compared to the off-resonance case, despite the presence of a thick metallic shell. In contrast to the widely studied case of plasmonic core-shell subwavelength particles, where the field enhancement occurs at the boundary of the metallic shell, the thick metallic shell surrounding the wavelength-scale dielectric core provides a strong energy confinement at the center of the core at longer wavelengths, where plasmonic effects are negligible. The observed enhancement can find applications for the probing of shielded materials and designing structures with engineered electromagnetic responses.

Engineered Gold Nanoshells Killing Tumor Cells: New Perspectives.

The current strategies to treat different kinds of cancer are mainly based on chemotherapy, surgery and radiation therapy. Unfortunately, these approaches are not specific and rather invasive as well. In this scenario, metal nano-shells, in particular gold-based nanoshells, offer interesting perspectives in the effort to counteract tumor cells, due to their unique ability to tune Surface Plasmon Resonance in different light-absorbing ranges. In particular, the Visible and Near Infrared Regions of the electromagnetic spectrum are able to penetrate through tissues. In this way, the light absorbed by the gold nanoshell at a specific wavelength is converted into heat, inducing photothermal ablation in treated cancer cells. Furthermore, inert gold shells can be easily functionalized with different types of molecules in order to bind cellular targets in a selective manner. This review summarizes the current state-of-art of nanosystems embodying gold shells, regarding methods of synthesis, bio-conjugations, bio-distribution, imaging and photothermal effects (in vitro and in vivo), providing new insights for the development of multifunctional antitumor drugs.

Theoretical Study of Fluorescence Spectroscopy of Quantum Emitters Coupled with Plasmonic Dimers and Trimers

We have developed a theory for the photoluminescence of dimer nanohybrids and trimer nanohybrids using the density matrix method. These nanohybrids are made from identical double metallic nanoshells embedded in an ensemble of quantum emitters. We consider that they are immersed in medical, biological, and chemical solutions. The dipole–dipole interaction between quantum emitters in the ensemble is calculated using the mean-field approximation. The effect of the dipole–dipole interaction has been included in the formulation of the photoluminescence. We have compared our theory with the experimental data of the ensemble of quantum emitters (ZnCdSeS-QDs) doped in chloroform and aqueous solutions. A good agreement between theory and experiment is found. We showed that the dipole–dipole interaction is stronger in the chloroform solution than that in the aqueous solution. Surface plasmon polariton resonances and electric fields are calculated for the metallic dimer and trimer by solving the Maxwell equations in the static wave approximation. The calculated surface plasmon polariton resonances agree with experimental data for an Au dimer and an Au trimer. We compare our theory with the photoluminescence experimental data of nanohybrids made from the ensemble of ZnCdSeS-QDs and the Au dimer and Au trimer. It is shown that the dipole–dipole interaction plays an important role in understanding the photoluminescence. We found that the intensity of the photoluminescence in the Au trimer nanohybrid is slightly higher than that in the Au dimer nanohybrid. This is because the surface plasmon polariton electric field emitted by the Au trimer is slightly larger than the electric field emitted by the Au dimer. We also found that two competing physical mechanisms, namely, the quenching and the enhancement, play important roles in these experiments. We showed that the quenching is due to the nonradiative decay rate, whereas the enhancement is due to the dipole–dipole interaction and surface plasmon polariton electric fields. These interesting findings may be useful in the fabrication of nanosensors for medical, biological, and chemical applications.

Investigating the effect of near infrared photo thermal therapy folic acid conjugated gold nano shell on melanoma cancer cell line A375

Nowadays, there is growing interest regarding the use of metal Nanoshells as targeted agents of Nano-photo thermal cancer therapy. This study was aimed at synthesis the folic acid (FA)-conjugated with silica @gold core-shell nanoparticles (FA-SiO2@AuNPs) for improving the treatment of melanoma cancer cells. The characterization data showed that the FA-SiO2@AuNPs is spherical in shape and its size is ∼73.7 nm. The intracellular uptake of FA-SiO2@AuNPs into melanoma cells (A375) was measured through the inductively coupled plasma, (∼47.7%). The cytotoxicity of nanoparticles was investigated on A375 and HDF (Human dermal fibroblast) cell lines. Cytotoxicity results indicated that there is no significant cytotoxicity in HDF cell lines treated with nanoparticles. MTT and flow cytometry results showed that the viability of A375 cells treated by SiO2@Au and FA-SiO2@AuNPs was decreased significantly to about 31% and 16% respectively. The higher toxicity of cancer cells was obtained for the cells exposed to 808 nm near-infrared (NIR) laser after incubation with FA-SiO2@AuNPs rather than the non-targeted SiO2@AuNPs. Furthermore, about 64% more cell death was observed for A-375 cells using both photothermal therapy and treatment with FA-SiO2@AuNPs compared to photothermal therapy. Additionally, the majority of the cell deaths were related to the apoptosis process, not necrosis. It can be concluded that FA-SiO2@AuNPs was an effective targeting agent for photothermal therapy in the treatment of melanoma.

Strong and tunable plasmonic field coupling and enhancement generating from the protruded metal nanorods and dielectric cores

Abstract Numerical investigation of resonant peak by modifying the number of protruded metal nanorods (MNRDs) and the core material in metal nanoshells for near field intensity are explored by means of the finite element method. The surface plasmon effect arising from the core cases with/without the protruded MNRDs was compared along with that arose from their solid counterparts. A strong and tunable field coupling and enhancement effects corresponding to the transverse surface plasmon resonance (SPR) and cavity plasmon resonance (CPR) modes are observed. It is found that the near field intensity spectra obtained from the silver and silver-shell nanorods with the protruded silver nanorods is approximately 2.5–3.0 times larger than that of the silver nanorods without the protruded silver nanorods. The peak resonance wavelength shows a red shift as the increasing of the permittivity in the core regions and the number of the protruded MNRDs. This indicates that the core regions and the protruded MNRDs can significantly mediate the EM waves coupling and enhancing the plasmonic effects and play a key role to tune the peak resonance wavelengths position. The investigated nanostructures offer multiple design freedoms to modulate the peak resonant wavelength and electromagnetic wave properties.

Numerical Analysis of Nonlocal Optical Response of Metallic Nanoshells

Nonlocal and quantum effects play an important role in accurately modeling the optical response of nanometer-sized metallic nanoparticles. These effects cannot be described by conventional classical theories, as they neglect essential microscopic details. Quantum hydrodynamic theory (QHT) has emerged as an excellent tool to correctly predict the nonlocal and quantum effects by taking into account the spatial dependence of the charge density. In this article, we used a QHT to investigate the impact of nonlocality and electron spill-out on the plasmonic behavior of spherical Na and Au nanoshells. We adopted a self-consistent way to compute the equilibrium charge density. The results predicted by QHT were compared with those obtained with the local response approximation (LRA) and the Thomas–Fermi hydrodynamic theory (TFHT). We found that nonlocal effects have a strong impact on both the near- and far-field optical properties of nanoshells, in particular, for the antibonding resonant mode. We also investigated the optical response of these systems for different thicknesses of the shell, both for Na and Au metals.

Resonant Terahertz Light Absorption by Virtue of Tunable Hybrid Interface Phonon–Plasmon Modes in Semiconductor Nanoshells

Metallic nanoshells have proven to be particularly versatile, with applications in biomedical imaging and surface-enhanced Raman spectroscopy. Here, we theoretically demonstrate that hybrid phonon-plasmon modes in semiconductor nanoshells offer similar advantages in the terahertz regime. We show that, depending on tm,n,nhe doping of the semiconductor shells, terahertz light absorption in these nanostructures can be resonantly enhanced due to the strong coupling between interface plasmons and phonons. A threefold to fourfold increase in the absorption peak intensity was achieved at specific values of electron concentration. Doping, as well as adapting the nanoshell radius, allowed for fine-tuning of the absorption peak frequencies.

A Compact Impedance Model of Plasmonic Nanoshell for Metamaterial Applications

Recent research in plasmonics demonstrated merging different materials and shapes to form complex geometries with improved optical response. One of the most extensively used nanostructure is the coated nanosphere (nanoshell), which finds its application in diverse fields of medical, science and engineering. In this paper, we propose a compact impedance model of metallic core nanoshell. The model is based on time-varying approach by solving full dipole equation for the metallic core and impedance of the dielectric shell is derived using near-field components of the dipole field. The expressions for the absorption and scattering cross-sectional areas, and their behavior with change in the dielectric function are derived for the first time for nanoshell using voltages, currents and circuit elements, with their equivalence compared with exact solution. Additionally, the effects of changes in nanoshell parameters (dielectric constants, thickness of shell layer and radii of core) on the resonance frequency predicted by the proposed impedance model are analyzed. The simplified impedance model is based on parallel resonance circuit and contributes to the better understanding the behavior of nanoshell and facilitate cost-effectiveness solution for the next generation nanoshell based metamaterials.

Tuning of the surface plasmon resonance of aluminum nanoshell near-infrared regimes.

The natural abundance of aluminum is far better than those of noble metals like silver and gold. Its plasmonic properties have not been explored in detail, as they generally lie in the ultraviolet region of the electromagnetic (EM) spectrum. Nevertheless, recent advanced research work in the literature predicts aluminum to be the next and best plasmonic material suitable for exciting cost-effective applications. Inspired by this, we have analyzed the optical properties of aluminum metal nanoshells using semi-analytical and numerical finite difference time domain models. In the semi-analytical model, we have discussed an electrostatic approach for nanoshell geometry and derived the exact Frolich condition and corresponding plasmon resonance peak position. These plasmonic peaks and their tunability in different regimes of the electromagnetic spectrum via the shell thickness are the main thrust of this work. For proof of concept, we have compared simulated and modeled results in different parameter domains and observed that both sets of results are in agreement with each other. We have also visualized the distribution of the electric field intensity near the aluminum nanoshell surface under SPR conditions, which covers a broad range of applications.

Oscillations of Fermi Energy of a Cylindrical Metal Nanoshell

Oscillations of Fermi Energy of a Cylindrical Metal Nanoshell

Enhancement of surface plasmon resonances on nonlinear optical properties in spherical dome semiconductor nanoshells

The interaction between a metallic nanopartical(MNP) and dome semiconductor nanoshells hybrid system on the nonlinear optical properties has been discussed. By means of the effective mass approximation and the compact-density-matrix methods, we have studied the enhancement of surface plasmon resonances(SPRs) on the second-harmonic generation(SHG) and nonlinear optical rectification. The results reveal that SHG and optical rectification are affected obviously by the SPRs of MNP, and the influence is related to the inner and external radius of the spherical dome semiconductor nanoshells.

Study of plasmonics in hybrids made from a quantum emitter and double metallic nanoshell dimer

We developed a theory for the fluorescence (FL) for quantum emitter and double metallic nanoshell dimer hybrids using the density matrix method. The dimer is made from two identical double metallic nanoshells, which are made of a dielectric core, a gold metallic shell and a dielectric spacer layer. The quantum emitters are deposited on the surface of the spacer layers of the dimers due to the electrostatic absorptions. We consider that dimer hybrids are surrounded by biological cells. This can be achieved by injecting them into human or animal cells. The surface plasmon polaritons (SPP) are calculated for the dimer using Maxwell’s equations in the static wave approximation. The calculated SPP energy agrees with experimental data from Zhai et al (2017 Plasmonics 12 263) for the dimer made from a silica core, a gold metallic nanoshell and a silica spacer layer. We have also obtained an analytical expression of the FL using the density matrix method. We compare our theory with FL experimental data from Zhai et al (2017 Plasmonics 12 263) where the FL spectrum was measured by varying the thickness of the spacer layer from 9 nm to 40 nm. A good agreement between theory and experiment is found. We have shown that the enhancement of the FL increases as the thickness of the spacer layer decreases. We have also found that the enhancement of the FL increases as the distance between the double metallic nanoshells in the dimer decreases. These are interesting findings which are consistent with the experiments of Zhai et al (2017 Plasmonics 12 263) and can be used to control the FL enhancement in the FL-based biomedical imaging and cancer treatment. These interesting findings may also be useful in the fabrication of nanosensors and nanoswitches for applications in medicine.

Ex Vivo Detection of Circulating Tumor Cells from Whole Blood by Direct Nanoparticle Visualization.

The detection of circulating tumor cells (CTCs) from blood samples can predict prognosis, response to systemic chemotherapy, and metastatic spread of carcinoma. Therefore, approaches for CTC identification is an important aspect of current cancer research. Here, a method for the direct visualization of nanoparticle-coated CTCs under dark field illumination is presented. A metastatic breast cancer cell line (4T1) was transduced with a non-native target protein (Thy1.1). Positive 4T1-Thy1.1 cells incubated with antibody-coated metallic nanoshells appeared overly bright at low magnification, allowing a quick screening of samples and easy visual detection of even single isolated CTCs. The use of a nontransduced cell line as control creates the ideal scenario to evaluate nonspecific binding. A murine metastatic tumor model with the 4T1-Thy1.1 cell line was also implemented. Blood was drawn from mice over the course of one month, and CTCs were successfully detected in all positive subjects. This work validates the use of metallic nanoshells as labels for direct visualization of CTCs while providing guidelines to a systematic development of nanotechnology-based detection systems for CTCs.

Monomer functionalized silica coated with Ag nanoparticles for enhanced SERS hotspots

Mesoporous silica (SiO2) spheres are well-known for their excellent chromatographic properties such as the relatively high specific surface, large pore volume, uniform particle size, narrow pore size distribution with favorable pore connectivity; whereas the noble metal Ag nanoparticles have unique size/shape dependant surface plasmon resonance with wide ranging applications. Thus, the desire to synchronize both their properties for specific applications has naturally prompted research in the design and synthesis of core-shell type novel nanoAg@mesoSiO2 nanocomposites, which display potential utility in applications such as photothermal therapy, photocatalysis, molecular sensing, and photovoltaics. In the present work, SiO2 spheres were carefully functionalized with the monomer, N-vinyl pyrrolidone (NVP), which cohesively controls the uniform mass transfer of Ag+ metal ions, thereby enabling its sequential reduction to zerovalent Ag (in the presence of slightly excess NaOH) by electron transfer from nucleophilic attack of the NVP vinyl group by the water molecules even under ambient conditions. Complete metal nanoshell coverage of the silica surface was obtained after multiple Ag deposition cycles, as systematically confirmed from the BET, TEM, optical and FTIR characterization. Our present Ag-coated silica spheres were directly utilized as viable SERS substrates with high sensitivity in contrast with other long chain polymer/surfactant coated silica spheres, owing to the presence of significant number of nanogaps enhanced SERS ‘hotspots’, which were methodically analyzed utilizing two example analytes, such as crystal violet (CV) and calendula officinalis (CaF).

Application of Metallic Nanomaterials in Nanomedicine.

In this chapter, we explain why metallic nanomaterials are used in nanomedicine. We have shown that the electron density in metallic nanomaterials oscillates and creates electron density waves. When laser light falls on metallic nanoparticles, light interacts with electron density waves. According to Einstein, light, which is electromagnetic waves, consists of particles called photons. Similarly, electron density waves are also made of particles called surface plasmons. Therefore, photons from laser light and surface plasmons from metallic nanostructures interact with each other and create new particles called surface plasmon polaritons. These new particles produce an intense light near the surface of metallic nanomaterials. We showed that this intense light is important in the application of metallic nanomaterials in nanomedicine. Further, we have applied metallic nanoparticles, single metallic nanoshells and double metallic nanoshells for treatment of cancer and detection of smaller tumors.

Evolution of ultrafine gold seed nanoparticles with temperature and time and synthesis of plasmonic nanoshells

Features of the evolution of ultrafine gold nanoparticles synthesized by the Duff method with temperature and time have been studied in relation to their use as seeds for the formation of plasmonic nanoshells. A quantitative relation has been revealed between the duration of preheating of such particles at a preset temperature and their size. The obtained relation indicates that Au nanoparticles grow mainly via the Ostwald ripening mechanism. Using anisotropic composite FeOOH/Ag particles as an example, it has been shown that the obtained information may be used to substantially decrease the duration of the synthesis of metal nanoshells on diverse cores.

Robustness of the Rabi Splitting under Nonlocal Corrections in Plexcitonics

We explore theoretically how nonlocal corrections in the description of the metal affect the strong coupling between excitons and plasmons in typical examples where nonlocal effects are anticipated to be strong, namely small metallic nanoparticles, thin metallic nanoshells or dimers with narrow separations, either coated with or encapsulating an excitonic layer. Through detailed simulations based on the generalised nonlocal optical response theory, which simultaneously accounts both for modal shifts due to screening and for surface-enhanced Landau damping, we show that, contrary to expectations, the influence of nonlocality is rather limited, as in most occasions the width of the Rabi splitting remains largely unaffected and the two hybrid modes are well distinguishable. We discuss how this behaviour can be understood in view of the popular coupled-harmonic-oscillator model, while we also provide analytic solutions based on Mie theory to describe the hybrid modes in the case of matryoshka-like single nanoparticles. Our analysis provides an answer to a so far open question, that of the influence of nonlocality on strong coupling, and is expected to facilitate the design and study of plexcitonic architectures with ultrafine geometrical details.

Optical/Electrical Integrated Design of Core–Shell Aluminum-Based Plasmonic Nanostructures for Record-Breaking Efficiency Enhancements in Photovoltaic Devices

Recently plasmonics has gained tremendous interest in solar cell research because it is capable of improving sunlight-conversion efficiencies. However, plasmonic photovoltaic nanostructures with both excellent optical properties and high electrical conductivities have not been developed, thus limiting the efficiency breakthrough. In this paper, we present an optical/electrical integrated design for plasmonic photovoltaic nanostructures by synthesizing core–shell nanomaterials: aluminum-coated copper nanoparticles. A copper nanocore was synthesized by chemical methods, and then an aluminum nanoshell was physically deposited on the nanocore surface. Strong light-scattering properties have been demonstrated due to the controllable morphology of the nanoparticles and the UV plasmon response of the aluminum nanoshells. Ultrahigh electrical conductivities have been achieved by the pure metallic nanoshells. Once the aluminum-based core–shell particles were integrated into high-efficiency amorphous silicon solar ...