Gold Nanocups Research Articles

Synthesis and Raman Performance Enhancement of Multilayer AuAg Heterostructures with Magnetic Resonance

Significant amplification of surface enhanced Raman scattering (SERS) signals can be achieved mainly by the electric field enhancement in metal core-shell nanostructures, and the enhanced magnetic field is rarely studied. In this study, we prepared multi-gap Au/AgAu core-shell hybrid nanostructures by using gold nanocup as the core. The overgrowth processes to grow one, two, and three layers of AgAu hybrid nanoshells can produce Au/AgAu1, Au/AgAu2, and Au/AgAu3 heteronanostructures. The strong plasmon coupling between the core and shell leads to significant electromagnetic field enhancement. Under the synergistic effect of electromagnetic plasmon resonance and plasmon coupling, Au/AgAu core-shell hybrid nanostructures exhibit excellent SERS signals. We also investigate the effect of the interstitial position of the rhodamine B (RhB) molecule on Raman enhancement in Au/AgAu3 heteronanostructures. This study can provide new ideas for the synthesis of multi-gap Raman signal amplifiers based on magnetic plasmon coupling.

Orientation-Dependent Interaction between the Magnetic Plasmons in Gold Nanocups and the Excitons in WS2 Monolayer and Multilayer.

The integration of two-dimensional transition metal dichalcogenides with plasmonic nanostructures is extremely attractive for the investigation of the resonance coupling between plasmons and excitons, which offers a framework for the study of cavity quantum electrodynamics and is of great potential for exploring diverse quantum technologies. Herein we report on the coupling between the magnetic plasmons supported by individual asymmetric Au nanocups and the excitons in WS2 monolayer and multilayer. Resonance coupling with the strength varying from weak to strong regimes is realized by adjusting the orientation of the individual Au nanocups on WS2 monolayer. Different energy detunings between the magnetic plasmons and the excitons are achieved by varying the size of the Au nanocup. The Rabi splitting energies extracted at zero detuning are up to 106 meV. The anticrossing feature is observed in the measured scattering spectra and simulated absorption spectra, which indicates that the resonance coupling between the magnetic plasmons in the Au nanocup and the excitons in WS2 monolayer enters the strongly coupled regime. A dependence of the coupling strength on the layer number is further observed when the Au nanocups are coupled with WS2 multilayer. Our study suggests a promising approach toward the realization of different coupling regimes in a simple hybrid system made of individual Au nanocups and two-dimensional materials.

Nanogold morphologies with the same surface chemistry provoke a different innate immune response: An in-vitro and in-vivo study

Gold nanomaterials (GNMs) have unique optical properties with less antigenicity, and their physicochemical properties have strong relation with an immunological response at bio-interface including antigenicity. An interpretation of this correlation would significantly impact on the clinical and theranostic applications of GNMs. Herein, we studied the effect of GNMs morphology on the cytotoxicity (in-vitro), innate immune responses, hepatotoxicity, and nephrotoxicity (in-vivo studies) using gold nano-cups (GNCs), porous gold nanospheres (PGNSs) and solid gold nano particles (SGNPs) coated with the same ligand to ensure similar surface chemistry. The cytotoxicity was assessed via sulfo-rhodamine B (SRB) assay, and the cytotoxicity data showed that morphological features at nanoscale dimensions like surface roughness and hollowness etc. have a significant impact on cellular viability. The biochemical and histopathological study of liver and kidney tissues also showed that all GNMs did not show any toxicity even at high concentration (100 μL). The relative quantification of cytokine gene expression of TNF-α, IFN-γ, IL-4, 1L-6, and 1L-17 (against each morphology) was checked after in-vivo activation in mice. Among the different nanogold morphologies, PVP stabilized GNCs (PVP-GNCs) showed the highest release of pro-inflammatory cytokines, which might be due to their high surface energy and large surface area for exposure as compared to other nanogold morphologies studied. The pro-inflammatory cytokine release could be suppressed by coating with some anti-inflammatory polymer, i.e., inulin. The in-vitro results of pro-inflammatory (TNF-α, IL-1) cytokines also suggested that all GNMs may induce activation of macrophages and Th1 immune response. The in-vivo activation results showed a decrease in mRNA expression of the cytokines (TNF-α, IFN-γ, IL-4, 1L-6 and 1L-17). Based on these findings, we proposed that the shape and morphology of GNMs control their immune response at nano-bio interface, and it must be considered while designing their role for different biomedical applications like immuno-stimulation and bio-imaging.

Gold nanocups with multimodal plasmon resonance for quantum-dot random lasing

Reduction of symmetry in plasmonic nanostructures may lead to great opportunities in controlling their photophysics of extinction, local field, light response, and plasmonic interactions. With their strong light scattering and unique modulation of field distribution, plasmonic nanocups hold great potential for applications in random laser, three-dimensional optical nanoantenna, and optical coherence tomography imaging. Here we demonstrate a novel and robust solution-phase synthesis approach to gold nanocups, which combines templating and seeded growth techniques to precisely control the size, morphology, and composition of the nanocups. Ripening is the key strategy in this wet-chemistry process to ensure primary anisotropic growth of gold within the cup-shaped space provided by each template, consisting of a silica nanosphere and a flexible resorcinol-formaldehyde resin shell. The resulting plasmonic nanocups possess three types of plasmon resonance modes, including axial, transverse S, and transverse P modes, determined by the polarization of the incident light. This robust and scalable synthesis allows the production of gold nanocups with high quality and efficiency, opening the door to unique photophysical properties and many potential applications, as demonstrated by their excellent performance in plasmonic quantum dot random lasing.

Nanozyme-Triggered Cascade Reactions from Cup-Shaped Nanomotors Promote Active Cellular Targeting.

Self-propelled nanomotors have shown enormous potential in biomedical applications. Herein, we report on a nanozyme-powered cup-shaped nanomotor for active cellular targeting and synergistic photodynamic/thermal therapy under near-infrared (NIR) laser irradiation. The nanomotor is constructed by the asymmetric decoration of platinum nanoparticles (PtNPs) at the bottom of gold nanocups (GNCs). PtNPs with robust peroxidase- (POD-) like activity are employed not only as propelling elements for nanomotors but also as continuous O2 generators to promote photodynamic therapy via catalyzing endogenous H2O2 decomposition. Owing to the Janus structure, asymmetric propulsion force is generated to trigger the short-ranged directional diffusion, facilitating broader diffusion areas and more efficient cellular searching and uptake. This cascade strategy combines key capabilities, i.e., endogenous substrate-based self-propulsion, active cellular targeting, and enhanced dual-modal therapy, in one multifunctional nanomotor, which is crucial in advancing self-propelled nanomotors towards eventual therapeutic agents.

Control of the emission from electric and magnetic dipoles by gold nanocup antennas.

The control of the emission from electric and magnetic dipoles is highly desired for the development of optic chips. Although the emission of electric dipole has been successfully controlled by plasmonic nanoantenna, the control of magnetic dipole emission is relatively difficult. Here, we systematically study the effect of electric and magnetic modes of Au nanocups on the emission of electric and magnetic dipoles. The emission of electric dipole can be enhanced by both the electric and magnetic mode of the Au nanocup, while the emission of the magnetic dipole is only increased by the magnetic mode. The enhancement exhibits wavelength dependence. The wavelength of the largest enhancement is determined by the resonance wavelength of electric and magnetic modes. The enhancement values for electric and magnetic dipoles are determined by the near-field electric and magnetic field enhancements, respectively. More importantly, the emission pattern of magnetic dipole is greatly modified by the magnetic mode of Au nanocup. The directional emission of magnetic dipole is first time realized by use of the magnetic mode of the Au nanocup. Our findings deepen the understanding of the plasmon-controlled emission of electric and magnetic dipoles and will be very helpful to the development of the nanophotonic chips.

Gold Nanocups Fabricated Using Two-Dimensional Colloidal Crystals and Simulation of Their Optical Trapping Force

Abstract Optical tweezers are powerful and flexible tools for manipulating micrometre-sized objects. Recently, metal nanostructures are gathering attention to trap nanometre-sized objects to utilize their plasmonic properties. Here, we discuss the preparation of gold nanocups (250-nm diameter) and their plasmonic properties for optical trapping. Gold was sputtered on a two-dimensional colloidal crystal (2DCC) and then de-coupled from the 2DCC via hydrofluoric acid etching, which resulted in a uniform gold nanocup array that was encapsulated in a flexible polymer resin. These nanocups in a resin can be transferred onto a variety of substrates. The optical trapping properties of gold nanocups are also discussed.

Flexible and Tunable 3D Gold Nanocups Platform as Plasmonic Biosensor for Specific Dual LSPR-SERS Immuno-Detection

Early medical diagnostic in nanomedicine requires the implementation of innovative nanosensors with highly sensitive, selective, and reliable biomarker detection abilities. In this paper, a dual Localized Surface Plasmon Resonance - Surface Enhanced Raman Scattering (LSPR- SERS) immunosensor based on a flexible three-dimensional (3D) gold (Au) nanocups platform has been implemented for the first time to operate as a relevant “proof-of-concept” for the specific detection of antigen-antibody binding events, using the human IgG - anti-human IgG recognition interaction as a model. Specifically, polydimethylsilane (PDMS) elastomer mold coated with a thin Au film employed for pattern replication of hexagonally close-packed monolayer of polystyrene nanospheres configuration has been employed as plasmonic nanoplatform to convey both SERS and LSPR readout signals, exhibiting both well-defined LSPR response and enhanced 3D electromagnetic field. Synergistic LSPR and SERS sensing use the same reproducible and large-area plasmonic nanoplatform providing complimentary information not only on the presence of anti-human IgG (by LSPR) but also to identify its specific molecular signature by SERS. The development of such smart flexible healthcare nanosensor platforms holds promise for mass production, opening thereby the doors for the next generation of portable point-of-care devices.

Photoluminescence Enhancement of CuInS2 Quantum Dots in Solution Coupled to Plasmonic Gold Nanocup Array.

A strong plasmonic enhancement of photoluminescence (PL) decay rate in quantum dots (QDs) coupled to an array of gold-coated nanocups is demonstrated. CuInS2 QDs that emit at a wavelength that overlaps with the extraordinary optical transmission (EOT) of the gold nanocup array are placed in the cups as solutions. Time-resolved PL reveals that the decay rate of the QDs in the plasmonically coupled system can be enhanced by more than an order of magnitude. Using finite-difference time-domain (FDTD) simulations, it is shown that this enhancement in PL decay rate results from an enhancement factor of ≈100 in electric field intensity provided by the plasmonic mode of the nanocup array, which is also responsible for the EOT. The simulated Purcell factor approaches 86 at the bottom of the nanocup and is ≈3-15 averaged over the nanocup cavity height, agreeing with the experimental enhancement result. This demonstration of solution-based coupling between QDs and gold nanocups opens up new possibilities for applications that would benefit from a solution environment such as biosensing.

Multiresonant layered plasmonic films

Multiresonant nanoplasmonic films have numerous applications in areas such as nonlinear optics and sensing and as spectral tags. Although techniques such as focused ion beam milling and electron beam lithography can produce high-quality multiresonant films, these techniques are expensive, serial processes that are difficult to scale at the manufacturing level. Here, we present the fabrication of multiresonant nanoplasmonic films using a layered stacking technique. Periodically spaced gold nanocup substrates were fabricated using self-assembled polystyrene nanospheres followed by oxygen plasma etching and metal deposition via magnetron sputter coating. By adjusting etch parameters and initial nanosphere size, it was possible to achieve an optical response ranging from the visible to the near-infrared. Singly resonant, flexible films were first made by performing peel-off using an adhesive-coated polyolefin film. Through stacking layers of the nanofilm, we demonstrate fabrication of multiresonant films at a fraction of the cost and effort compared with top-down lithographic techniques.

Tamper indicating gold nanocup plasmonic films

The spectral signatures of nanoplasmonic films are both robust and tailorable with optical responses ranging from the visible to the near-infrared. We present the development of flexible, elastomeric nanoplasmonic films consisting of periodic arrays of gold nanocups as tamper indicating films. Gold nanocups have polarization-sensitive optical properties that may be manufactured into films that offer unique advantages for tamper indication. These flexible films can be made quickly and at low-cost using the commercially available monodisperse polystyrene nanospheres through self-assembly followed by plasma etching, metal deposition, and lift-off from a sacrificial substrate. The polarization- and angle-dependent optical spectroscopic measurements were performed to characterize the fabricated films. Using polarization-sensitive hyperspectral imaging, we demonstrate how these films can be applied to tamper indication and counterfeit resistance applications.

Directional light scattering from individual Au nanocup

We investigate the optical scattering properties of gold nanocup with different orientation and fractional height by full vector finite element method. All of the scattering cross section, the distribution of electric field intensity, and the ability of directional light scattering are simulated, respectively. It is demonstrated that the scattering cross section of Au nanocup is a superposition of scattering spectrum of a transverse mode and an axial mode. The wavelength and the intensity of the maximum value of the scattering cross section increase initially then reduce with the fractional height increasing for transverse mode, while they increase monotonously with the fractional height increasing for axial mode. Furthermore, the calculation results show that the ability of redirecting incident light of Au nanocup mainly depends on the transverse mode. And the deflected angle of scattering increases with the fractional height of Au nanocup decreasing. These results indicate that Au nanocup has a promising application in the planar plasmon devices.

Colloidal Gold Nanocups with Orientation-Dependent Plasmonic Properties.

Colloidal gold nanocups are synthesized through single-vertex-initiated gold deposition on PbS nanooctahedrons and subsequent selective dissolution of the PbS component. They possess strong magnetic plasmon resonance and exhibit remarkable orientation-dependent plasmonic properties when deposited on flat substrates. They can also effectively couple s-polarized light into the interfacial region between the nanocup and substrate.

From porous gold nanocups to porous nanospheres and solid particles – A new synthetic approach

We report a versatile approach for the synthesis of porous gold nanocups, porous gold nanospheres and solid gold nanoparticles. Gold nanocups are formed by the slow reduction of gold salt (HAuCl4⋅3H2O) using aminoantipyrene (AAP) as a reducing agent. Adding polyvinylpyrrolidone (PVP) to the gold salt followed by reduction with AAP resulted in the formation of porous gold nanospheres. Microwave irradiation of both of these porous gold particles resulted in the formation of slightly smaller but solid gold particles. All these nanoparticles are thoroughly characterized by UV–visible spectroscopy, scanning electron microscopy (SEM), high resolution transmission electron microscopy (HR-TEM) and bright-field tomography. Due to the larger size, porous nature, low density and higher surface area, these nanomaterials may have interesting applications in catalysis, drug delivery, phototherapy and sensing.

Optofluidically Tuned Fluorescence Enhancement by Plasmonic Nanocup Arrays

ABSTRACTWe demonstrate fluidically tuned fluorescence enhancement on the colorimetric substrate with the plasmonic effects induced by the periodic gold nanocup arrays. The fluorescence enhancement by the plasmonic effect has been studied extensively by varying the geometries of nanostructures or the morphology of nanoparticles. In this study, however, the fluorescence enhancement without changing these parameters but simply by varying surrounding media on the colorimetric plasmonic surface is accomplished. The dynamic responses of fluorescence from self-assembled monolayer of dyes on the surface were monitored by flowing various fluids with different refractive indices. The dependence of the radiative decay rate as well as the scattering cross-section on the surrounding dielectric properties results into the selective enhancement of the fluorescence intensity, having a maximum at different surrounding refractive index for different fluorophores with different emission band centers.

Fabrication of a large, ordered, three-dimensional nanocup array

Metallic nanocups provide a unique method for redirecting scattered light by creating magnetic plasmon responses at optical frequencies. Despite considerable development of nanocup fabrication processes, simultaneously achieving accurate control over the placement, orientation, and geometry of nanocups has remained a significant challenge. Here we present a technique for fabricating large, periodically ordered arrays of uniformly oriented three-dimensional gold nanocups for manipulating light at subwavelength scales. Nanoimprint lithography, soft lithography, and shadow evaporation were used to fabricate nanocups onto the tips of polydimethylsiloxane nanopillars with precise control over the shapes and optical properties of asymmetric nanocups.

Fabrication and Characterization of Large, Perfectly Periodic Arrays of Metallic Nanocups

Fabrication of plasmonic resonance devices composed of large arrays of highly ordered gold nanocups is presented. The nanostructures are generated from periodic photoresist templates created by interference lithography and subsequent reflow, deposition, and dislodging. The nanocups are hemispherical in shape and arranged in both rectangular and hexagonal arrays with periods of ~500 nm. Their ability to support surface plasmonic resonances is manifested experimentally by reflectance spectroscopy. Theoretical modeling to ascertain the plasmonic spectra of these nanostructures is performed. The computed spectra of the rectangular structure are in qualitative agreement with the measurements. A weaker correlation observed for the hexagonal structure is explained by its more intricate symmetry which complicates the spectral response.