Plasmonic Core-shell Nanoparticles Research Articles

Predicting and Probing the Local Temperature Rise Around Plasmonic Core-Shell Nanoparticles to Study Thermally Activated Processes.

Ultrafast spectroscopy can be used to study dynamic processes on femtosecond to nanosecond timescales, but is typically used for photoinduced processes. Several materials can induce ultrafast temperature rises upon absorption of femtosecond laser pulses, in principle allowing to study thermally activated processes, such as (catalytic) reactions, phase transitions, and conformational changes. Gold-silica core-shell nanoparticles are particularly interesting for this, as they can be used in a wide range of media and are chemically inert. Here we computationally model the temporal and spatial temperature profiles of gold nanoparticles with and without silica shell in liquid and gas media. Fast rises in temperature within tens of picoseconds are always observed. This is fast enough to study many of the aforementioned processes. We also validate our results experimentally using a poly(urethane-urea) exhibiting a temperature-dependent hydrogen bonding network, which shows local temperatures above 90 °C are reached on this timescale. Moreover, this experiment shows the hydrogen bond breaking in such polymers occurs within tens of picoseconds.

Gold-copper oxide core-shell plasmonic nanoparticles: the effect of pH on shell stability and mechanistic insights into shell formation.

Plasmonic nanoparticles play an important role in applications for chemical sensing, catalysis, medicine, and biosensing. The localized surface plasmon resonance (LSPR) of a nanoparticle is determined by factors such as size, shape, and the local dielectric environment. Here, we report a simple colloidal synthesis method to create core-shell plasmonic nanoparticles with a gold core and a copper oxide (Cu2O) shell. The gold cores are particles of various shapes and sizes, including nanorods, nanobipyramids, and nanoshells, and the Cu2O shell is on the order of 30-40 nm thick. The growth of the oxide shell red shifts the plasmonic absorption of the gold core particle by up to 250 nanometers, resulting in a particle that can absorb into the near-infrared (NIR). Additionally, we report the unique ability to immediately remove and regrow the oxide shell by simple changes to the solution pH. We demonstrate the repeated dissolution and nucleation of the oxide shell through the addition of an acid and a base, respectively. The process is confirmed by characterization using Ultraviolet-Visible-Near-IR (UV-Vis-NIR) spectroscopy and electron microscopy of the particles. After several iterations of this process, we report the formation of large Cu2O spheres, where Cu2O nucleation on other Cu2O particles is favored over the gold nanoparticles. In addition, we provide insight into the role of ligands in shell formation.

Investigation of Light Scattering by Plasmonic Core-Shell Nanoparticles via the Discrete Sources Method Accounting for the Surface Quantum Effect

Investigation of Light Scattering by Plasmonic Core-Shell Nanoparticles via the Discrete Sources Method Accounting for the Surface Quantum Effect

Nonlinear chaotic dynamics in nonlocal plasmonic core-shell nanoparticle dimer.

Plasmonic nanoparticles can be employed as a promising integrated platform for lumped optical nanoelements with unprecedentedly high integration capacity and efficient nanoscale ultrafast nonlinear functionality. Further minimizing the size of plasmonic nanoelements will lead to a rich variety of nonlocal optical effects due to the nonlocal nature of electrons in plasmonic materials. In this work, we theoretically investigate the nonlinear chaotic dynamics of the plasmonic core-shell nanoparticle dimer consisting of a nonlocal plasmonic core and a Kerr-type nonlinear shell at nanometer scale. This kind of optical nanoantennae could provide novel switching functionality: tristable, astable multivibrators, and chaos generator. We give a qualitative analysis on the influence of nonlocality and aspect ratio of core-shell nanoparticles on the chaos regime as well as on the nonlinear dynamical processing. It is demonstrated that considering nonlocality is very important in the design of such nonlinear functional photonic nanoelements with ultra-small size. Compared to solid nanoparticles, core-shell nanoparticles provide an additional freedom to adjust their plasmonic property hence tuning the chaotic dynamic regime in the geometric parameter space. This kind of nanoscale nonlinear system could be the candidate for a nonlinear nanophotonic device with a tunable nonlinear dynamical response.

Left-handed optical torque on dipolar plasmonic nanoparticles induced by Fano-like resonance

We theoretically and numerically demonstrate that Fano-like resonance can induce a left-handed optical torque on a dipolar plasmonic core-shell nanoparticle in the interference optical field composed of two linearly polarized plane waves. It is shown that the optical torque on the dipolar plasmonic nanoparticle is significantly enhanced at the Fano-like resonance, and its direction is opposite to that of the angular momentum of the incident field, termed Fano-like resonance-induced left-handed optical torque. The extinction spectra exhibit that the Fano-like resonance stems from the coupling between a narrow electric quadrupole dark mode and a broad electric dipole bright mode. In addition, such Fano-like resonance-induced left-handed optical torque can flexibly be tailored by the particle morphology. To further trace the physical origin of the left-handed optical torque, we derive an analytical expression of optical torques up to electric quadrupole in generic monochromatic optical fields based on the multipole expansion theory. The results obtained from our analytical expression show that the left-handed optical torque comes completely from the electric quadrupole terms while other terms from the electric dipole make no contribution. Our results may open a new avenue for tailoring optical torques on plasmonic structures.

Identifying high performance photosensitizer with simultaneous enhancement in fluorescence and singlet oxygen generation, from ‘(Ag/Au)-aggregation-induced emission-active fluorogen’ theranostic nanoparticles

Photodynamic therapy (PDT) is a non-invasive medical technique that combines photosensitizer (PS) molecules and light for cancer treatment. Driven by the need for more personalized medicine, shortened irradiation time and treatment efficiency of PDT are required. Herein, a library of novel theranostic nanoparticle systems for personalized medicine in PDT of cancer is reported. Ag and Au nanoparticles in a size range of 40–50 nm are prepared and used subsequently to synthesize core-shell plasmonic nanoparticles with various thicknesses, either with silica or polymer spacer. Metal-enhanced fluorescence and singlet oxygen generation (SOG) studies are performed for a naphthalene-linked pyridine-based neutral triarylethene as AIE-active PS molecule, by adsorbing on the Ag and Au core-shell nanoparticles. The factors that are varied during the study are the composition of the spacer, and the spacer length. Notably, the enhancement in fluorescence and SOG of the adsorbed AIEgen are observed at the same distance from the metallic surface, resulting from short-range near field plasmonic effect for all the theranostic PS prepared with Ag/Au. The best result, 7.9 fold enhancement in fluorescence and 10.4-fold enhancement in SOG, is observed on loading AIEgen on ∼42 nm Au nanoparticles with polymer spacer, showing promising advancement for image-guided PDT. The probable reasons behind the observed outcomes, are analyzed and discussed in detail, with the help of the Jablonski diagram of the PS molecule. The obtained results from the study has the potential to replace or support the conventional radiation therapy and chemotherapy with serious adverse effects.

Plasmonic core–shell nanoparticles of Ag@TiO2 for photocatalytic degradation of Rhodamine B

Plasmonic core–shell nanoparticles of Ag@TiO2 for photocatalytic degradation of Rhodamine B

Fishing unfunctionalized SERS tags with DNA hydrogel network generated by ligation-rolling circle amplification for simple and ultrasensitive detection of kanamycin

Simple assay format-based SERS methods for sensitive target substance analysis is of great significance for the development of on-site monitoring biosensors. Herein, taking the typical antibacterial kanamycin (KANA) as a subject, a simple, highly sensitive and specific SERS aptasensor was developed by manipulating DNA hydrogel network to fish plasmonic core-shell nanoparticles. A competitive binding mode of aptamer, ligation-rolling circle amplification (L-RCA), gap-containing Au@Au nanoparticles (GCNPs) with embedded Raman reporters were integrated into the sensor. In the presence of KANA, the double stranded DNA (dsDNA) structure of the aptamer was disrupted, and the released primers were used to construct two kinds of circularized padlock probes (CPPs) which were partially complementary. DNA hydrogel network was formed through the intertwining and self-assembly of two RCA-generated single stranded DNA (ssDNA) chains, during which GCNPs and magnetic beads (MBs) were entangled and incorporated. Finally, KANA quantification was successfully achieved through the quantification of the DNA hydrogel. Overall, this novel SERS aptasensor realized a simple and ultrasensitive quantification of KANA down to 2.3 fM, plus excellent selectivity, and precision even for real food samples. In view of innovative fusion across L-RCA-based DNA hydrogel and SERS technique, the proposed method has promising potential for application in on-site detection and quantification of trace food contaminants.

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.

Modelling core-shell plasmonic nanoparticles as homogenous systems: An effective refractive index approach

Core-shell plasmonic nanoparticles have attracted significant interest for use in a vast number of applications such as optoelectronics, solar energy, and drug delivery. However, modeling core-shell nanoparticles as two distinct regions, namely the core and the shell leads to computational complexity, especially in large systems. Additionally, most metallic plasmonic nanoparticles develop a self-limiting oxide shell, creating in effect, a metal-metal oxide core-shell system. Effective medium theories have emerged as a technique to study core-shell nanoparticles as a single homogenous system. However, current effective medium theories are limited due to their low accuracy, especially for larger core and shell thicknesses (>50nm). Here, we present a novel method that determines an effective refractive index enabling spherical core-shell nanoparticles, of varying core and shell radii and material composition, to be represented as a single homogenous nanoparticle; thus allowing for quick, efficient and simple calculations with accuracies similar to that obtained by using analytical solutions given by Mie Theory. This technique holds prospects to model the properties of core-shell nanoparticles for applications such as plasmonic enhanced solar cell simulations, for quantification of heat generated by plasmonic nanoparticles (thermoplasmonics) etc. This technique will hence enable rapid and accurate calculations of the optical properties of core-shell nanoparticles for a variety of technologies.

Optical and Dielectric Properties of Plasmonic Core–Shell Nanoparticles: Fe2O3/Au and Fe3O4/Au

Optical and Dielectric Properties of Plasmonic Core–Shell Nanoparticles: Fe2O3/Au and Fe3O4/Au

Modeling of optical properties of plasmonic core–shell nanoparticles embedded in glass for filtering of solar radiation

The computer results of optical properties of core–shell nanoparticles embedded in glass have been presented for the selection of their parameters for effective filtering and extinction of solar infrared energy. Optical properties of TiO2-Au, Fe3O4-Au, NiO-Au, SiO2-Au particles are theoretically investigated and analyzed in the spectral interval 200–2500 nm.Core–shell SiO2-Au nanoparticles have been selected for following investigation on the base of their more appropriate optical properties in visible spectrum in comparison with others. Influence of nanoparticle parameters (radii, shell thicknesses, concentrations) on their optical properties (efficiency factors of absorption, scattering, extinction and their correlations, scattering indicatrixes, optical transmittance of nanostructured glass layer) has been investigated. It was established, that spherical SiO2-Au nanoparticles with the core radii of about 60-80 nm, shell thicknesses 5, 10 nm and concentrations ∼109-1010 cm−3 embedded in glasses can be applied for effective extinction of infrared solar radiation. The medium transmittance of nanostructured glasses with nanoparticles can be achieved 70%–80% and more in visible spectrum that is sufficient for appropriate visibility. These results can be used for the development of nanostructured energy protective glasses that prevents the penetration of infrared solar energy inside buildings or cars.

Significant optical force enhancements of nanostructure with balanced gain and loss.

In this paper, we theoretically analyze the optical force between a pair of active and passive plasmonic core-shell nanoparticles (NPs). The optical force between the NPs can be either attractive or repulsive near the critical point while the passive dimer provides only attractive force. We reveal that the reversal of attractive or repulsive force is determined by the relative phase of electric dipole (ED) modes, which can be strongly affected by the gain and loss coefficient κ. Compared with the passive dimer with the same size, the active-passive dimer can exhibit a very high repulsive force (about two orders of magnitude) while remaining the same order magnitude attractive force when the value of coefficient is 0.345. Interestingly, we find that the position of the maximum repulsive force occurs near the critical point. We also investigate the influence of variations in geometrical parameters of the dimer and polarization angle on the force. Finally, the numerical results demonstrate that when the dimer is illuminated by a laser beam, the attractive and repulsive forces can also be achieved. The manipulation of optical force can find potential in optical sorting and transport of NPs.

Modelling Core-Shell Plasmonic Nanoparticles as Homogenous Systems: An Effective Refractive Index Approach

Core-shell plasmonic nanoparticles have attracted significant interest for use in a vast number of applications such as optoelectronics, solar energy, and drug delivery. However, modeling core-shell nanoparticles as two distinct regions, namely the core and the shell leads to computational complexity, especially in large systems. Additionally, most metallic plasmonic nanoparticles develop a self-limiting oxide shell, creating in effect, a metal- metal oxide core-shell system. Effective medium theories have emerged as a technique to study core-shell nanoparticles as a single homogenous system. However, current effective medium theories are limited due to their low accuracy, especially for larger core and shell thicknesses (>50nm). Here, we present a novel method that enables accurate representation of core-shell nanoparticles as a homogeneous particle using a single set of refractive indices, for a vast range of core and shell radii, and material compositions; thus allowing for quick and efficient simulations with accuracy similar to that of the analytical solutions obtained based on Mie Theory. We hope that this technique will enable rapid and accurate calculations for core-shell plasmonic applications.

Physical Unclonable Anticounterfeiting Electrodes Enabled by Spontaneously Formed Plasmonic Core–Shell Nanoparticles for Traceable Electronics

AbstractCounterfeit electronics are a growing problem for the electronic information industry worldwide, so developing unbreakable security tags is crucial to ensure the trustworthiness and traceability of electronics. Traditional anticounterfeiting and trace solutions rely on reproducible deterministic processes and additional labels, which can still be copied or faked by counterfeiters. Herein, physical unclonable functions enabled by spontaneously formed plasmonic core–shell nanoparticles on electrodes are proposed to ensure label‐free traceable electronics, giving a practical solution to fight against counterfeit electronics. Random hemispherical core–shell nanoparticles are intentionally introduced on the metal electrode of different semiconductors (Si, GaAs, and GaN) from Ni/Au bilayer heterofilms by rapid thermal annealing, which can be integrated with electronics seamlessly, with no negative effect on electrical properties. The position, size, and shape of nanoparticles are random and uncontrollable; the corresponding scattering patterns, intensity, and spectra can work as nanofingerprints of the electrode, proving multidimensional unclonable labels with large encoding capacity suitable for electrodes smaller than several micrometers. It can be further combined with machine vision and artificial intelligence to identify and track electronics automatically and efficiently. The anticounterfeiting electrodes also show good thermal robustness and mechanical stability, opening up a prospect for practical anticounterfeiting of electronics.

Atomic Insights into the Evolution of Three-Dimensional Molecular Junctions in Plasmonic Core–Shell Nanoparticles

The plasmonic molecular junctions are of wide interest for the studies of physics, chemistry, and materials science. For the three-dimensional (3D) molecular junctions inside plasmonic core–shell n...

Improving light harvesting and charge extraction of polymer solar cells upon buffer layer doping

It is an important strategy to improve the performance of polymer solar cells (PSCs) by incorporating metal nanoparticles into functional layers. Herein, gold (Au)@titanium dioxide (TiO2) plasmonic core-shell nanoparticles (PCSNPs) are synthesized and doped into zinc oxide (ZnO) as hybrid electron transport layer in PSCs. Improved light trapping and electrical conductivity are achieved through localized surface plasma resonance of Au@TiO2 PCSNPs. As a result, the short-circuit current density is apparently enhanced, while remaining the unchanged open-circuit voltage. The maximum PCE of 8.801% is obtained when 1.5 wt% Au@TiO2 PCSNPs are introduced into the ZnO layer. This study provides a new inspiration for the development of high efficiency PSCs.

Electronic structures associated with enhanced photocatalytic activity in nanogap-engineered g-C3N4/Ag@SiO2 hybrid nanostructures

Graphitic carbon nitride (g-C3N4) has attracted considerable attention with regard to its use in photocatalytic solar hydrogen production by the splitting of water. High charge carrier recombination critically limits the photocatalytic activity of g-C3N4. Plasmonic metal nanoparticles that can generate localized surface plasmon resonance (LSPR) have been suggested to enhance the harvesting of visible light and to improve water splitting efficiency. However, direct contact between metal nanoparticles and g-C3N4 reduces the hydrogen generation efficiency owing to energy loss by Förster resonance energy transfer (FRET), which competes with plasmon resonance energy transfer (PRET). Decorating g-C3N4 with Ag@SiO2 core-shell plasmonic nanoparticles increases its photocatalytic ability. Tuning the size of the SiO2 nanogap can optimize the photocatalytic performance of g-C3N4/Ag@SiO2, which involves a trade-off between PRET and FRET. X-ray absorption spectroscopy (XAS) is utilized to investigate the electronic structure of g-C3N4 and its modulation with Ag@SiO2. In situ XAS reveals the dynamics of the charge carriers under solar illumination. Analytic results suggest charge redistribution, shifting of the conduction band, modification of the unoccupied states, and consequent improvement in photocatalytic activity by solar illumination. This work sheds light on the effect of LSPR on this photocatalyst with reference to its electronic structure.

Reducing the loss of electric field enhancement for plasmonic core–shell nanoparticle dimers by high refractive index dielectric coating

Plasmonic nanoparticle (NP) dimers, generating highly intense areas of electric field enhancement named hot spots, have been playing a vital role in various applications like surface enhanced Raman scattering. For stabilization and functionalization, such metallic NPs are often coated with dielectric shells, yet suffer from a rapid degeneration of the hot spot with the increase of the shell thickness. Herein, it is demonstrated that the use of appropriately high refractive dielectric coatings can greatly reduce the loss of local electric field enhancement, maintaining usable hot spots. Two mechianisms work synergistically. Firstly, the high refractive index dielectric coating enables a great leap of the local electric fields reaching the gap, which follows the boundary conditions at the interface within electrodynamics. Secondly, owing to its strong Mie resonances that can participate in the plasmon hybridization, the high refractive index dielectric coating contributes to a strong light coupling effect in terms of improving the light absorption. Taking advantage of the proposed physical process decomposition, both the resonance shift and local electric field enhancement can be elaborated. These findings should be of significant importance in extended applications of surface enhanced spectroscopies and related plasmonic devices based on hot spots.

TUNABLE SURFACE PLASMON RESONANCES OF Au@TiO2 CORE-SHELL NANOPARTICLES ON THE DSSC (DYE SENSITIZED SOLAR CELLS) PERFORMANCE

Plasmonic core-shell nanoparticles, i.e. gold can improve the efficiency of Dye-sensitized Solar Cell by increase the light harvesting due to the strong near-field effect LSPR (Localized Surface Plasmon Resonance). To achieve maximum enhancement, the morphology of core-shell need to be optimized with coated either by insulator such as semiconductor, i.e. TiO2. In this paper, morphology of Au@TiO2 core-shell precisely control by various TiO2 volume and systematically study its influence on the plasmonic enhancement effect. A gold solution was prepared using Turkevich method. The crystal structure of the powders was determined by powder X-ray diffraction (XRD). The optical properties were measured by UV-Vis absorption spectroscopy using UV-Vis Lambda 750. The photocurrent action spectra or IPCE in visible light spectrum was obtained by adjusting wavelength of incident light, i.e. series connection of halogen lamp and monochromator. UV-Vis absorption spectra of core–shell showed the position of the surface plasmon Au band in the range of 500–550 nm. According to UV-Vis characterization, all samples studied show weak surface plasmon resonance response (~520 to 550 nm) as indicative of the thick TiO2 shells for individual core-shell Au@TiO2.Tunable Surface Plasmon Resonances of Au@TiO2 Core-shell Nanoparticles on the DSSC (Dye Sensitized Solar Cells) Performance