Au Nanoshells Research Articles

The effect of Au nanoshells with controllable aggregation on SERS enhancement

Au nanoshells consisting of a dielectric core with a metallic layer of nanometer thickness exhibit tunable local surface plasmon resonance property. The core size has a great effect on the aggregation state of formed Au nanoshells, which leads to the variation of the intensity of surface enhanced Raman scattering (SERS). This paper reports a controllable aggregation for the fabrication of Au nanoshells with different size of core. TEM results demonstrated that formed Au nanoshells showed obvious aggregation with decreasing the size of core. By SERS analysis, different aggregation state leads to different SERS signal intensity. By comparison, Au nanoshells with core size of 50–80 nm exhibit high SERS enhancement effect.

Growth of silver-coated gold nanoshells with enhanced linear and nonlinear optical responses

Silver-coated gold nanoshells with 1,4-BDT molecules as the spacer (Ag/BDT/Au) were synthesized on the surface of SiO2 nanospheres. The surface plasmon resonance of Au/SiO2 and Ag/BDT/Au/SiO2 nanoparticles with single and double shells were tuned by adjusting the thickness of Au and Ag nanoshells. The enhanced local field in the gap of Au and Ag shells is demonstrated by measuring Raman scattering and nonlinear refraction. The results show that the Raman intensity is enhanced by 17 times and the nonlinear refractive index is enhanced by 30 % due to the growth of Ag shells.

Erratum: “Plasmon resonance based analysis of a single protein conjugated Au nanoshell” [Biointerphases 9, 031017 (2014)

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ChemInform Abstract: Near‐Infrared Light‐Responsive Nanomaterials in Cancer Therapeutics

AbstractReview: 172 refs.

Plasmon resonance based analysis of a single protein conjugated Au nanoshell.

The authors perform a numerical calculation of a gold nanoshell, having either a silica core or a hollow one, interacting with incident electromagnetic radiation and aggregated with a single protein on its surface, by using the discrete dipole approximation. The protein model accounts for a tertiary structure that may contain internal cavities, while the entire structure is placed either in vacuum or a uniform host medium. The authors further analyze the near field pattern by a spherical harmonic transform. Our results identify the interactions that account for the observed extinction peak and wavelength shift in related optical experiments. The theoretical basis provided in this work may be used not only to identify a single protein conjugated nanoparticle, but also to determine the cavity content of the protein by its refractive index properties, determined from optical measurements.

Photothermolysis of lymphatic endothelial cells by gold nanoshell-mediated hyperthermia.

Tumor-associated lymphatics and lymphangiogenesis have been shown to play important roles in promoting tumor growth and metastasis. However, the lymphatic system has received much less attention as a target of intervention in cancer treatment compared to the blood vascular system. In this study, we explored the feasibility of photothermal therapy targeting the lymphatic system as a strategy for inhibiting lymphatics-mediated tumor metastasis. Specifically, photothermolysis of lymphatic endothelial cells (LECs) via gold nanoshell-mediated hyperthermia was investigated. Near-Infrared-absorbing Au nanoshells (AuNSs) were synthesized and used as the photothermal coupling agent. After 24-hr incubation, significant amount of the AuNSs were taken up by murine simian virus lymphatic endothelial cells with minimal cytotoxicity. Thermally-induced injury to LECs was found to occur above a threshold temperature of 46 degrees C. Preliminary data also suggested apoptosis as the mechanism of thermally-induced cell death in this temperature range. In a proof-of-concept experiment, AuNS-mediated photothermal heating was found to induce cell death in statistically higher percent of LECs incubated with AuNSs after 15-min laser irradiation compared to the controls. We believed that the findings in this study represent the first step in developing AuNS-mediated photothermal therapy as a potential strategy to disrupt tumor-associated lymphatics.

An active metallic nanomatryushka with two similar super-resonances

The optical properties of a simple metallic nanomatryushka (nanosphere-in-a-nanoshell) with gain have been investigated theoretically. The spaser (surface plasmon amplification by stimulated emission of radiation) phenomena can be observed at two critical wavelengths in the active metallic nanomatryushkas. With increasing the gain coefficient of the middle layer, a similar super surface plasmon (SP) resonance is first found at the ω−+|1 mode of the active nanoparticles and then breaks down. With further increasing the gain coefficient, another similar super-resonance occurs at the ω−−|1 mode. The near-field enhancements in the active nanomatryushkas also have been greatly amplified at the critical wavelengths for ω−+|1 and ω−−|1 modes. It is further found that the amplifications of SPs in the active Ag–SiO2–Au nanoshell are strongest in four kinds of nanoshells and hence the largest near fields. The giant near-field enhancement can greatly enhance the Raman excitation and emission.

A computational study of the double-bands plasmonic light scattering of Al 2 O 3 coated Al nanoshells in the deep-ultraviolet range

Abstract The tunable scattering cross section of oxide layer-coated Al nanoshell has been computationally studied as a function of wavelength. The calculation results show that the two resonance light scattering (RLS) peaks of Al nanoshell have higher frequency and greater intensity than that of Au and Ag nanoshell. Both of the two scattering peaks, which are corresponding to anti-symmetric and symmetric plasmon coupling, take place in the ultraviolet range. And the anti-symmetric scattering peak could be tuned down to the deep-ultraviolet wavelength below 200 nm. By increasing radius and dielectric constant of the inner core, or decreasing the thickness of the oxide layer, the anti-symmetric scattering peak with short wavelength could be enhanced and has greater intensity than that of symmetric scattering peak with long wavelength, which is different from that of Au and Ag nanoshells. Obtaining intense RLS peaks from Al nanoshell at deep-ultraviolet region presents a potential for the application of ultra-sensitive biosensing, ultraviolet material characterization, and ultraviolet nanoscale imaging.

Impurity-induced plasmon damping in individual cobalt-doped hollow Au nanoshells.

The optical properties of plasmonic nanoparticles in the size range corresponding to the electrostatic, or dipole, limit have the potential to reveal effects otherwise masked by phase retardation. Here we examine the optical properties of individual, sub-50 nm hollow Au nanoshells (Co-HGNS), where Co is the initial sacrificial core nanoparticle, using single particle total internal reflection scattering (TIRS) spectroscopy. The residual Co present in the metallic shell induces a substantial broadening of the homogeneous plasmon resonance line width of the Co-HGNS, where the full width at half-maximum (fwhm) broadens proportionately with increasing Co content. This doping-induced line broadening provides a strategy for controlling plasmon line width independent of nanoparticle size, and has the potential to substantially modify the relative decay channels for localized nanoparticle surface plasmons.

Au Nanomatryoshkas as Efficient Near-Infrared Photothermal Transducers for Cancer Treatment: Benchmarking against Nanoshells

Au nanoparticles with plasmon resonances in the near-infrared (NIR) region of the spectrum efficiently convert light into heat, a property useful for the photothermal ablation of cancerous tumors subsequent to nanoparticle uptake at the tumor site. A critical aspect of this process is nanoparticle size, which influences both tumor uptake and photothermal efficiency. Here, we report a direct comparative study of ∼90 nm diameter Au nanomatryoshkas (Au/SiO2/Au) and ∼150 nm diameter Au nanoshells for photothermal therapeutic efficacy in highly aggressive triple negative breast cancer (TNBC) tumors in mice. Au nanomatryoshkas are strong light absorbers with 77% absorption efficiency, while the nanoshells are weaker absorbers with only 15% absorption efficiency. After an intravenous injection of Au nanomatryoshkas followed by a single NIR laser dose of 2 W/cm2 for 5 min, 83% of the TNBC tumor-bearing mice appeared healthy and tumor free >60 days later, while only 33% of mice treated with nanoshells survived the same period. The smaller size and larger absorption cross section of Au nanomatryoshkas combine to make this nanoparticle more effective than Au nanoshells for photothermal cancer therapy.

Correction to “Anomalously Strong Electric Near-Field Enhancements at Defect Sites on Au Nanoshells Observed by Ultrafast Scanning Photoemission Imaging Microscopy”

Correction to “Anomalously Strong Electric Near-Field Enhancements at Defect Sites on Au Nanoshells Observed by Ultrafast Scanning Photoemission Imaging Microscopy”

ChemInform Abstract: Anisotropic Gold Nanoparticles: Synthesis, Properties, Applications, and Toxicity

AbstractReview: 429 refs.

Functional Core/Shell Drug Nanoparticles for Highly Effective Synergistic Cancer Therapy

Gold (Au)-nanoshelled 10-hydroxycamptothecin nanoparticles (HCPT NPs) are developed with combination of photothermal therapy and chemotherapy for highly effective cancer therapy. The strong near-infrared (NIR) absorbance from Au nanoshells endows the nanocomposites photothermal effects and on-demand drug release. Notably, the drug-loading content reaches up to 63.7 wt%, which is much higher than that in the previously reported nanovehicles systems. Both in vitro and in vivo studies indicate that the combined local specific chemotherapy with external NIR photothermal therapy demonstrates a synergistic effect, which is significantly better than either of them alone. More importantly, due to the high drug-loading content and efficient photothermal effects of the nanocomposites, 100% in vivo tumor elimination is achieved at a low laser irradiation power density of 1 W cm(-) (2) without weight loss and tumor recurrence. No obvious systematic toxicity is observed for the injected mice, indicating the good biocompatibility of this kind of multifunctional drug nanocomposites. This work highlights the great potential of drug-nanostructure-based multifunctional core/shell nanpocomposite for highly efficient cancer therapy.

Gold Binary‐Structured Arrays Based on Monolayer Colloidal Crystals and Their Optical Properties

A simple and flexible route is presented to fabricate a gold binary-structured ordered array by one step based on non-shadow deposition on a plasma etching-induced dualistic monolayer colloidal crystal. Such a Au binary-structure array is built of hexagonally arranged nanoshells and nanorings which stand between two adjacent nanoshells. Six gold nanorings surround each nanoshell. The obtained arrays exhibit both the controllable surface-plasmon-resonance (SPR) properties of Au nanoshells and the strong electromagnetic-field-enhancement effects of Au nanorings, with the high structural stability of ordered arrays, and show promising potential as the substrate of surface-enhanced Raman scattering (SERS)-based devices. The method could also be suitable for fabrication of other material binary-structured arrays. This study is important in designing and fabricating basal materials for the next generation of multifunctional nanostructured devices.

Comparison of Au and Ag nanoshells׳ metal-enhanced fluorescence

The average enhancement factors of Au and Ag nanoshells (NSs) were analyzed theoretically to compare their overall performances on metal-enhanced fluorescence. We used the Mie theory and dyadic Green׳s functions to calculate the excitation rate and apparent quantum yield of NS interacting with a plane wave and a dipole, respectively, and then to obtain the enhancement factor. Moreover, the average enhancement factor (AEF) of NS on the fluorescence of a nearby molecule was obtained by averaging all possible orientations and locations of the molecule with a constant distance from NS. Our results show that the maximum AEF of Au NS occurs at the wavelength of the dipole mode, which is broadband. In contrast, the maximum AEF of Ag NS is at the narrowband quadrupole mode. In addition, the Stokes shift effect on AEF was studied for Au and Ag NSs.

Anisotropic Gold Nanoparticles: Synthesis, Properties, Applications, and Toxicity

Anisotropic gold nanoparticles (AuNPs) have attracted the interest of scientists for over a century, but research in this field has considerably accelerated since 2000 with the synthesis of numerous 1D, 2D, and 3D shapes as well as hollow AuNP structures. The anisotropy of these nonspherical, hollow, and nanoshell AuNP structures is the source of the plasmon absorption in the visible region as well as in the near-infrared (NIR) region. This NIR absorption is especially sensitive to the AuNP shape and medium and can be shifted towards the part of the NIR region in which living tissue shows minimum absorption. This has led to crucial applications in medical diagnostics and therapy ("theranostics"), especially with Au nanoshells, nanorods, hollow nanospheres, and nanocubes. In addition, Au nanowires (AuNWs) can be synthesized with longitudinal dimensions of several tens of micrometers and can serve as plasmon waveguides for sophisticated optical devices. The application of anisotropic AuNPs has rapidly spread to optical, biomedical, and catalytic areas. In this Review, a brief historical survey is given, followed by a summary of the synthetic modes, variety of shapes, applications, and toxicity issues of this fast-growing class of nanomaterials.

Mn-porphyrin conjugated Au nanoshells encapsulating doxorubicin for potential magnetic resonance imaging and light triggered synergistic therapy of cancer.

A theranostic agent was successfully fabricated by the formation of Au nanoshell around poly(lactic acid) nanoparticles entrapping doxorubicin, followed by linking a Mn-porphyrin derivative on the Au shell surface through polyethylene glycol. The resulted agent exhibited excellent colloidal stability and long blood circulation time due to introducing polyethylene glycol. The grafting Mn-porphyrin onto the nanoparticle surface endowed a greatly improved relaxivity (r1 value of 22.18 mM-1s-1 of Mn3+), favorable for accurate cancer diagnosing and locating the tumor site to guide the external near infrared (NIR) laser irradiation for photothermal ablation of tumors. The in vitro experiments confirmed that the agent exhibited an efficient photohyperthermia and a light triggered and stepwise release behavior of doxorubicin due to the high NIR light absorption coefficient of Au nanoshell. The in vivo experiments showed that the combination of chemotherapy and photothermal therapy through such theranostic agent offered a synergistically improved therapeutic outcome compared with either therapy alone, making it a promising approach for cancer therapy. Therefore, such theranostic agent can be developed as a smart and promising nanosystemplatform that integrates multiple capabilities for both effective contrast enhanced magnetic resonance imaging and synergistic therapy.

Hybrid Photonic–Plasmonic polarization beam splitter (HPPPBS) based on metal–silica–silicon interactions

In this work, a broadband efficient hybrid Photonic–Plasmonic polarization beam splitter (HPPPBS) based on metal–silica–silicon interactions is proposed and investigated numerically. This device contains two silicon (Si) nanofibers with specific examined dimensions, a silica (SiO2) waveguide and a straight chain of Au nanoshells which is encompassed by silica host. All of the mentioned fibers and waveguide are deposited on a Mg2F crystal host. It is shown that this structure is working properly at near infrared region (NIR), specifically at telecommunication wavelength (λ≈1550 nm). Furthermore, relevant optical characteristics have been examined and studied, thoroughly. The quality of polarization splitting is demonstrated for both transverse electric (TE) and magnetic (TM) modes in separate figures. Simulation results corroborate that the sensitivity and accuracy of the superstructure during polarization dividing and light propagating are noticeable in comparison to analogous devices. Finite-difference time-domain method (FDTD-M) is utilized to examine the optical properties of the presenting structure.

Tailoring LSPR-Based Absorption and Scattering Efficiencies of Semiconductor-Coated Au nanoshells

Absorption and scattering efficiencies of semiconductor-coated Au nanoshell have been studied by the extended Mie theory for their possible solar cell, optical imaging, and photothermal applications, etc. The effect of Au shell layer thickness, core size, and surrounding medium on the absorption and scattering efficiencies at the localized surface plasmon resonance (LSPR) wavelengths has been reported. It has been found that both the absorption and scattering efficiencies get blue-shifted with an increase in Au shell layer thickness from 2 to 10 nm and with an increase in surrounding refractive index whereas the corresponding LSPR peaks shift towards red. It has also been found that the spectra are red-shifted with an increase in the core radius from 20 to 40 nm while keeping the shell thickness same. The effect of shell thickness on the absorption peak position and absorption linewidth has also been studied. Hence, the optical response of both CdSe- and CdTe-coated Au nanoshells can be tuned and controlled from the visible to the near-infrared (NIR) region of the electromagnetic (EM) spectrum. Finally, the CdSe-coated Au nanoshell exhibits high scattering and absorption efficiencies in comparison to the CdTe-coated nanoshell.

Anomalously Strong Electric Near-Field Enhancements at Defect Sites on Au Nanoshells Observed by Ultrafast Scanning Photoemission Imaging Microscopy

Multiphoton photoelectron emission from individual SiO2 core–Au shell nanoparticles supported on an ITO substrate is studied with ultrafast scanning photoemission imaging microscopy. Higher than expected photoemission yields (∼105-fold) and a strong sensitivity to excitation laser polarization direction indicate the presence of anomalously high electromagnetic field enhancement areas (i.e., “hot spots”) on the surface of Au nanoshells. The measured magnitude of the photoelectron current is consistent with 1–2 localized hot spots on each nanoparticle exhibiting electric near-field enhancement factors of nominally |E|/|E0| ∼ 50–100. Secondary electron microscopy (SEM) studies reveal asperities on the surface of each nanoparticle that most likely arise due to postsynthetic Ostwald ripening of the Au shell layer. However, no correlation is found between these features and the laser polarization that yields the maximum photoelectron emissivity, indicating that the hot spots responsible for the observed high el...