Plasmonic Shell Research Articles

Plasmonic semi shells derived from simultaneous in situ gold growth and anisotropic acid etching of ZIF-8 for photothermal ablation of metastatic breast tumor

Open nanoshells such as nanobowls or nanocups collectively described as ‘semi shells’ have unique plasmonic properties due to their lack of symmetry. So far, their fabrication was based on multistep and laborious methods such as solid state sputter coating or selective deposition/etching using sacrificial templates. In this work, we report a rapid one step colloidal synthetic protocol for PEGylated semi-shell (SS) fabrication by simultaneous facet specific anisotropic chemical etching of rhombic dodecahedral ZIF-8 and heterogenous nucleation & growth of gold. The SS possesses a strong localized surface plasmon resonance in the near-infrared region, which is retained after surface passivation with polyethylene glycol and subsequent cryopreservation for extended shelf-life. Freshly reconstituted PEGylated SS was found to be safe & non-toxic in healthy C57BL/6 mice post intravenous administration. The PEGylated SS displayed significant photothermal efficiency of ~37% with 808 nm laser irradiation. Preclinical assessment of intra-tumoral photothermal efficacy indicated complete remission of primary breast tumor mass with insignificant metastasis to vital organs in 4T1 FL2 tumor bearing CD1 nude mice. Further, PEGylated SS mediated photothermal therapy also yielded morbidity free survivael of 75% for up to 90 days, indicating their potential to significantly improve outcomes in advanced breast tumors.

Crescent-shaped Janus nanoassemblies of gold nanoparticles and AIEgens: Enhancing plasmonic and fluorescent activities for colorimetric and ratiometric fluorescence lateral flow immunoassay

Herein, crescent-shaped Janus nanoassemblies (Au-AIENPs) with high plasmonic and fluorescent activities are prepared by co-assembling oleylamine-coated gold nanoparticles (OA-AuNPs) and red-emitting aggregation-induced emission luminogens (AIEgens) in separate compartments of polymer nanoparticles. The obtained Au-AIENPs show typical Janus heterostructures, where AIEgens preferentially aggregate to form fluorescent core and OA-AuNPs are distributed in the polymer matrix to form a crescent-shaped plasmonic shell, thus resulting in effective spatial separation of OA-AuNPs and AIEgens to achieve the balance between plasmonic and fluorescent signals and reduce the mutual interference between signals. Taking advantage of the excellent plasmonic and fluorescent activities of Au-AIENPs, we successfully established a colorimetric and ratiometric fluorescence dual-mode lateral flow immunoassay (Au-AIENPs-RLFIA) for the visual and quantitative detection of aflatoxin B1 (AFB1) in corn sample. Under the developed conditions, the visual detection limit (vLOD) of the Au-AIENPs-RLFIA for colorimetric and ratiomentic fluorescence detection was 0.62 ng/mL and 0.02 ng/mL, respectively, while the quantitative LOD (qLOD) for ratiomentic fluorescence mode was as low as 0.0076 ng/mL. The above results indicate that the designed Janus Au-AIENPs are promising as dual-signal output probes and hold great potential for improving flexible dual-mode detection of various targets on the LFIA platform.

Extrinsic chirality tailors Stokes parameters in simple asymmetric metasurfaces.

Metasurfaces tailor electromagnetic confinement at the nanoscale and can be appropriately designed for polarization-dependent light-matter interactions. Adding the asymmetry degree to the desing allows for circular polarizations of opposite handedness to be differently absorbed or emitted, which is of interest in fields spanning from chiral sensing to flat optics. Here, we show that simple, low-cost asymmetric metasurfaces can control Stokes parameters in the transmitted far-field. With only 50 nm of asymmetric plasmonic shells on self-assembled polystyrene nanospheres, our metasurfaces allow for great spectral and incident angle tunability. We first investigated broadband extrinsic chirality in metasurfaces with asymmetric plasmonic semishells; we found high extinction circular dichroism (CD) in the near-infrared range. We then excited it with linear polarization and performed hyperspectral Stokes polarimetry on the transmitted field. We showed that the S3 parameter follows the behavior of CD in extinction, and that the output field position on the Poincaré sphere can be widely controlled by using the incidence angle and wavelength. Furthermore, simulations agreed well with the experiments and showed how the near-field chiro-optical response influences the extrinsic chiral behavior in absorption and the polarization state of the transmitted field.

Giant Raman radiation from molecules in a spherical metal shell

The work considers an electrodynamic model of radiation from molecules placed in a metal shell. The model qualitatively describes the enhancement of the surface-enhanced Raman scattering (SERS) signal from spherical nanoparticles coated with a thin silver film. The change in the SERS signal is calculated depending on the thickness of the metal nanolayer on top of the spherical particles. The radiating molecular dipole interacts with the metal shell and excites surface plasmons. Plasmonic oscillations reach a maximum when the frequency of the dipole is close to the plasmon resonance of the metal shell, and the dipole itself is close to the plasmonic shell. It has been theoretically shown that the intensity of secondary radiation generated by spherical nanoparticles coated with a silver film several nanometers thick can reach up to six or more orders of magnitude. The effect of a tenfold amplification of the SERS signal was experimentally demonstrated using the example of a large ensemble of single polystyrene microspheres with an average diameter of about 300 nm, coated with a silver nanolayer, which have characteristic Stokes frequencies of 1001 cm-1, 1602 cm-1. We believe that the tenfold enhancement of Raman scattering is due to the electromagnetic amplification mechanism.

Modulation of plasmonic chiral shell growth on gold nanorods via nonchiral surfactants.

Recently, in combination with seed-mediated growth, thiolated chiral molecule-guided growth has shown great promise in obtaining chiral plasmonic nanostructures. Previously, with the assistance of chiral cysteines (Cys), we realized helical growth of plasmonic shells on gold nanorod (AuNR) seeds dispersed in cetyltrimethylammonium bromide (CTAB) solution. Herein, we further studied the roles of non-chiral cationic surfactants in tuning the helical growth. Both the counter anion and the hydrocarbon chain length of the surfactants were found to affect the formation of helical shells greatly. In particular, we exhibited surfactant-modulated conversion of the chiral shell deposition mode between layer growth and island growth. By optimizing growth conditions, an obvious plasmonic circular dichroism (PCD) response could be achieved for the island helical shell. Our findings demonstrated promising potential of nanochemical synthesis in fabricating chiral plasmonic nanostructures with small structural sizes.

Plasmon-Enhanced C-C Bond Cleavage toward Efficient Ethanol Electrooxidation.

Ethanol, as a sustainable biomass fuel, is endowed with the merits of theoretically high energy density and environmental friendliness yet suffers from sluggish kinetics and low selectivity toward the desired complete electrooxidation (C1 pathway). Here, the localized surface plasmon resonance (LSPR) effect is explored as a manipulating knob to boost electrocatalytic ethanol oxidation reaction in alkaline media under ambient conditions by appropriate visible light. Under illumination, Au@Pt nanoparticles with plasmonic core and active shell exhibit concurrently higher activity (from 2.30 to 4.05 A mgPt-1 at 0.8 V vs RHE) and C1 selectivity (from 9 to 38% at 0.8 V). In situ attenuated total reflection-surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) provides a molecular level insight into the LSPR promoted C-C bond cleavage and the subsequent CO oxidation. This work not only extends the methodology hyphenating plasmonic electrocatalysis and in situ surface IR spectroscopy but also presents a promising approach for tuning complex reaction pathways.

Chiral Plasmonic Shells: High-Performance Metamaterials for Sensitive Chiral Biomolecule Detection.

Low-cost and large-area chiral metamaterials (CMs) are highly desirable for practical applications in chiral biosensors, nanophotonic chiral emitters, and beyond. A promising fabrication method takes advantage of self-assembled colloidal particles, onto which metal patches with defined orientation are created using glancing angle deposition (GLAD). However, using this method to make uniform and well-defined CMs over macroscopic areas is challenging. Here, we fabricate a uniform large-area colloidal particle array by interface-mediated self-assembly and precisely control the structural handedness of chiral plasmonic shells (CPSs) using GLAD. Strong chiroptical signals arise from twisted currents at the main, corner, and edge of CPSs, allowing a balance between strong chiroptical and high transmittance properties. Our shell-like chiral geometry shows excellent sensor performance in detecting chiral molecules due to the formation of uniform superchiral fields. Systematic investigations optimize the interplay between peak and null point resonances in different CPSs and result in a record consistency chiral sensor parameter U, i.e., 3.77 for null points and 0.0867 for peaks, which are about 54 and 1.257 times larger than the highest value (0.068) of previously reported CMs. The geometrical chirality, surface plasmonic resonance, chiral surface lattice resonance, and chiral sensor performance evidence the chiroptical effect and the excellent chiral sensor performance.

Multifunctional plasmonic micro/nanobeads for sensitive suspension array assay and mass spectrometry analysis

Plasmonic micro/nanobeads exhibit unique physicochemical properties attributed to their localized surface plasmon resonance (LSPR), enabling use in sensitive suspension array assays and matrix-assisted laser deposition/ionization mass spectrometry (MALDI-MS) analysis. Herein, we report a facile method for the preparation of magnetic plasmonic micro/nanobeads by the combination of Shirasu porous glass (SPG) membrane emulsification and polydopamine (PDA)-assisted in-situ reduction. The magnetic responsiveness properties endowed by doped Fe3O4 nanoparticles result in easy and complete separation of unwanted components during the preparation and bio-reaction processes. In addition, the coverage degree of the plasmonic shell can be flexibly controlled. As a result of the significant metal-enhanced fluorescence effect, as-prepared plasmonic microbeads enable the sensitive detection of alpha-fetoprotein (AFP) and deoxyribonucleotide (DNA) in suspension array with detection limits of 0.11 ng mL−1 and 1.65 fmol mL−1, respectively, 8.6 times and 2 orders of magnitude higher than unmodified microbeads. Furthermore, as-prepared plasmonic nanobeads can be used as a matrix for MALDI-MS to allow the detection of low molecular weight biological molecules. As little as 0.2 pmol of proline and serine can be detected in a sample as small as 0.5 μL. This work provides a general strategy for the design of multifunctional plasmonic micro/nanomaterials that will help promote further advancements in sample analysis.

Silent region barcode particle arrays for ultrasensitive multiplexed SERS detection

Suspension arrays are a critical components of next generation multiplexed detection technologies. Current fluorescence suspension arrays are limited by a multiplexed coding ceiling and difficulties with ultrasensitive detection. Raman mode is a promising substitute, but the complex spectral peak distributions and extremely weak intrinsic signal intensity severely diminish Raman signal performance in suspension arrays. To address these limitations, we constructed a Raman suspension array system using plasmonic microbeads as barcode substrates and Au nanoflowers as reporter carriers. The well-designed shell morphology and plasmonic microbead composition enabled significant surface enhancement Raman scattering (SERS) such that we were able to adjust silent region Raman-coding intensity levels. Due to synergistic SERS effects from the plasmonic shell and the multi-branched Au nanoflower nanostructure, the reporting signal was greatly improved, enabling ultrasensitive detection of 5-plexed lung cancer markers. Detection in patient serum samples demonstrated good consistency with the standard electrochemiluminescence method. Thus, this silent region SERS barcode-based suspension array is a developmental advance for modern multiplexed biodetection, potentially providing a powerful early disease screening and diagnosis tool.

Engineering a strong and stable ultraviolet chiroptical effect in a large-area chiral plasmonic shell.

Ultraviolet chiral metamaterials (UCM) are highly desired for their strong interaction with the intrinsic resonance of molecules and ability in manipulating the polarization state of high energy photons, but rarely reported to date due to their small feature size and complex geometry. Herein, we design and fabricate a kind of novel ultraviolet chiral plasmonic shell (UCPS) by combing the stepwise Al deposition and colloid-sphere assembled techniques. The cancellation effect originated from the disorder lattices of micro-domains in the colloid monolayer has been successfully overcome by optimizing the deposition parameters, and a strong CD signal of larger than 1 deg in the UV region is demonstrated both in simulation and experiment. This strong ultraviolet chiroptical resonances mainly come from the surface chiral lattice resonance mode, the whispering gallery mode and also the interaction between neighbor shells, and can be effectively tuned by changing structural parameters, for example, the sphere diameter, or even slightly increasing the deposition temperature in experiment. To improve the stability, the fabricated UCPSs are protected by N2 in the deposition chamber and then passivated by UV-ozone immediately after each deposition step. The formed UCPS show an excellent stability when exposing in the atmospheric environment. The computer-aided geometrical model, electromagnetic modes, and the tunable chiroptical resonance modes have been systematically investigated.

New Insights into the Magnetic Properties of CoFe2O4@SiO2@Au Magnetoplasmonic Nanoparticles

We report the successful synthesis and a complete magnetic characterization of CoFe2O4@SiO2@Au magnetoplasmonic nanoparticles. The CoFe2O4 magnetic nanoparticles were prepared using the hydrothermal method. A subsequent SiO2 shell followed by a plasmonic Au shell were deposited on the magnetic core creating magnetoplasmonic nanoparticles with a core–shell architecture. A spin-glass-type magnetism was shown at the surface of the CoFe2O4 nanograins. Depending on the external magnetic field, two types of spin-glass were identified and analyzed in correlation with the exchange field acting on octahedral and tetrahedral iron sites. The magnetization per formula unit of the CoFe2O4 core is not changed in the case of CoFe2O4@SiO2@Au nanocomposites. The gold nanoparticles creating the plasmonic shell show a giant diamagnetic susceptibility, dependent on their crystallite sizes.

Full Coverage of the Solar Spectrum and Beyond Using All-Manganese Plasmonic Shell Array

Full Coverage of the Solar Spectrum and Beyond Using All-Manganese Plasmonic Shell Array

Core-shell metallic alloy nanopillars-in-dielectric hybrid metamaterials with magneto-plasmonic coupling

Combining plasmonic and magnetic properties, namely magneto-plasmonic coupling, inspires great research interest and the search for magneto-plasmonic nanostructure becomes considerably critical. Here we designed a nanopillar-in-matrix structure with core–shell alloyed nanopillars for both BaTiO3 (BTO)-Au0.5Co0.5 (AuCo) and BTO-Au0.25Cu0.25Co0.25Ni0.25 (AuCuCoNi) hybrid systems, i.e., ferromagnetic alloy cores (e.g., Co or CoNi) with plasmonic shells (e.g., Au or Au/Cu). These core–shell alloy nanopillars are uniformly embedded into a dielectric BTO matrix to form a vertically aligned nanocomposite (VAN) structure. Both hybrid systems present excellent epitaxial quality and interesting multi-functionality, e.g., high magnetic anisotropy, magneto-optical coupling response, tailorable plasmonic resonance wavelength, tunable hyperbolic properties and strong optical anisotropy. These alloyed nanopillars-in-matrix designs provide enormous potential for complex hybrid material designs with multi-functionality and demonstrate strong interface enabled magneto-plasmonic coupling along with plasmonic and magnetic performance.

Gain-Assisted Optical Pulling Force on Plasmonic Graded Nano-Shell with Equivalent Medium Theory

The tunable optical pulling force on a graded plasmonic core-shell nanoparticle consisting of a gain dielectric core and graded plasmonic shell is investigated in the illumination of a plane wave. In this paper, the electrostatic polarizability and the equivalent permittivity of the core-shell sphere are derived and the plasmonic enhanced optical pulling force in the antibonding and bonding dipole modes of the graded nanoparticle are demonstrated. Additionally, the resonant pulling force occurring on the dipole mode is shown to be dependent on the aspect ratio of the core-shell particle, which is illustrated by the obtained equivalent permittivity. This shows that the gradation of the graded shell will influence the plasmonic feature of the particle, thus further shifting the resonant optical force peaks and strengthening the pulling force. The obtained results provide an additional degree of freedom to manipulate nanoparticles and give a deep insight into light–matter interaction.

Determination of pseudo-refractive index in self-assembled ligand layers from spectral shift of surface plasmon resonances in colloidal silver nanoplates

Abstract We examined systematically how self-assembled monolayers (SAMs) of different mercaptoacids affect the spectral shift of the localized surface plasmon resonance in silver nanoplates and nanospheres. We observed a clear trend in the magnitude of a redshift with a molecular length or the SAM thickness within a homologous series of aliphatic mercaptoacids: the thicker shell the stronger the red shift. Using classic Mie theory for plasmonic core-dielectric shell spheres and oblate spheroids we developed the method for determination of a pseudo-refractive index in SAM of different molecules and obtained a good correlation with the reference refractive indices for bulk long-chain aliphatic acids, but only in case of silver nanoplates. Calculations for silver core–shell nanospheres gave overestimated values of refractive index perhaps due to restrictions of Mie theory on the minimum particle size.

Formation of Co–Au Core–Shell Nanoparticles with Thin Gold Shells and Soft Magnetic ε-Cobalt Cores Ruled by Thermodynamics and Kinetics

Bimetallic core–shell nanoparticles (CSNPs), where a ferromagnetic core (e.g., Co) is surrounded by a noble-metal thin plasmonic shell (e.g., Au), are highly interesting for applications in biomedi...

Nitride‐Oxide‐Metal Heterostructure with Self‐Assembled Core–Shell Nanopillar Arrays: Effect of Ordering on Magneto‐Optical Properties

Magneto-optical (MO) coupling incorporates photon-induced change of magnetic polarization that can be adopted in ultrafast switching, optical isolators, mode convertors, and optical data storage components for advanced optical integrated circuits. However, integrating plasmonic, magnetic, and dielectric properties in one single material system poses challenges since one natural material can hardly possess all these functionalities. Here, co-deposition of a three-phase heterostructure composed of a durable conductive nitride matrix with embedded core-shell vertically aligned nanopillars, is demonstrated. The unique coupling between ferromagnetic NiO core and atomically sharp plasmonic Au shell enables strong MO activity out-of-plane at room temperature. Further, a template growth process is applied, which significantly enhances the ordering of the nanopillar array. The ordered nanostructure offers two schemes of spin polarization which result in stronger antisymmetry of Kerr rotation. The presented complex hybrid metamaterial platform with strong magnetic and optical anisotropies is promising for tunable and modulated all-optical-based nanodevices.

Quality of Control in the Tavis–Cummings–Hubbard Model

In this paper, the Discrete Sources Method has been extended to describe the influence of the geometry asymmetry of a core-shell particle accounting for the effect of spatial dispersion inside the plasmonic metal shell. We found that varying the plasmonic shell thickness has more influence on the near field intensity distribution then on the average enhancement factor. Besides, we demonstrates that the effect of spatial dispersion can decrease the near field intensity up to 60% of its value and it provides a small blue shift.

The Effects of a Varied Gold Shell Thickness on Iron Oxide Nanoparticle Cores in Magnetic Manipulation, T1 and T2 MRI Contrasting, and Magnetic Hyperthermia.

Fe3O4–Au core–shell magnetic-plasmonic nanoparticles are expected to combine both magnetic and light responsivity into a single nanosystem, facilitating combined optical and magnetic-based nanotheranostic (therapeutic and diagnostic) applications, for example, photothermal therapy in conjunction with magnetic resonance imaging (MRI) imaging. To date, the effects of a plasmonic gold shell on an iron oxide nanoparticle core in magnetic-based applications remains largely unexplored. For this study, we quantified the efficacy of magnetic iron oxide cores with various gold shell thicknesses in a number of popular magnetic-based nanotheranostic applications; these included magnetic sorting and targeting (quantifying magnetic manipulability and magnetophoresis), MRI contrasting (quantifying benchtop nuclear magnetic resonance (NMR)-based T1 and T2 relaxivity), and magnetic hyperthermia therapy (quantifying alternating magnetic-field heating). We observed a general decrease in magnetic response and efficacy with an increase of the gold shell thickness, and herein we discuss possible reasons for this reduction. The magnetophoresis speed of iron oxide nanoparticles coated with the thickest gold shell tested here (ca. 42 nm) was only ca. 1% of the non-coated bare magnetic nanoparticle, demonstrating reduced magnetic manipulability. The T1 relaxivity, r1, of the thick gold-shelled magnetic particle was ca. 22% of the purely magnetic counterpart, whereas the T2 relaxivity, r2, was 42%, indicating a reduced MRI contrasting. Lastly, the magnetic hyperthermia heating efficiency (intrinsic loss power parameter) was reduced to ca. 14% for the thickest gold shell. For all applications, the efficiency decayed exponentially with increased gold shell thickness; therefore, if the primary application of the nanostructure is magnetic-based, this work suggests that it is preferable to use a thinner gold shell or higher levels of stimuli to compensate for losses associated with the addition of the gold shell. Moreover, as thinner gold shells have better magnetic properties, have previously demonstrated superior optical properties, and are more economical than thick gold shells, it can be said that “less is more”.

One-Minute Synthesis of a Supramolecular Hydrogel from Suspension-Gel Transition and the Derived Crystalline, Elastic, and Photoactive Aerogels.

Solutions or sols are commonly employed as the starting materials for the preparation of supramolecular hydrogels; however, suspension-based synthesis has been much less reported because of inhomogeneity and quick sedimentation of large particles in a suspension. Further, it remains a technical challenge to derive supramolecular aerogels directly from the parental hydrogels owing to the ease of structural collapse during water removal. Herein, we report a suspension-gel transition for the ultrafast synthesis of a new supramolecular hydrogel simply by adding AgNO3 into the aqueous suspension of cyanuric acid-melamine (CAM) aggregates. With the activation of preadded ammonia, Ag ions instantly reacted with the CAM particles, transforming into N-Ag(I)-N coordinating bonded supramolecular nanofibers; simultaneously, the suspension converted to a hydrogel without the use of polymer cross-linkers or external stimulus. Upon simple freeze-drying, a highly crystalline fibrous aerogel with a cellular network was obtained, which possessed a porosity up to 99.7% and a density as low as 4.8 mg/cm3, enabling remarkable oil uptake capacities (100 times of its weight). The supramolecular aerogel demonstrated intrinsic elasticity, which should arise from the cellular structure and elastic character of the nanofiber skeletons. Notably, the aerogel showed high compatibility to incorporate a range of external substances for further functionalization exemplified by polymeric carbon nitride (PCN, a metal-free semiconductor) included gels. The loaded PCN resulted in enhanced mechanical strength and endowed the aerogel unique photoactivity, i.e., in situ reducing Ag(I) into Ag nanoparticles upon light illumination and thus forming a plasmonic shell over the aerogel with potential applications in sensing and catalysis.