Optical properties of VO2 spherical nanoparticles

Localized surface plasmon resonance H2 detection by MoO3 colloidal nanoparticles fabricated by the flame synthesis method

We present theoretical modeling of the local surface plasmon resonance (LSPR) induced by hollow nanoshell spheres assisted with a graphene shell, aiming to examine their potential for use as efficient narrowband absorbers in the infrared wavelength region. We investigate two designs of hollow nanoparticles; namely, a hollow graphene nanosphere with a single graphene shell, and a hollow nanosphere with double shells comprising a graphene shell wrapped around a silver shell. The electric field in each region of the nanoshell is determined by solving the Laplace equation of the potential within the electrostatic approximation (the nanoshell radius [Formula: see text]50[Formula: see text]nm). Using the calculated polarizability of nanoshells, we derive analytical expressions for the absorption and scattering cross-sections. We show that in both proposed nanocomposite models, the graphene shell affords an ultra-narrow LSPR with an absorption efficiency significantly higher than the scattering efficiency. In addition, the graphene-assisted LSPR can be tuned through the visible and infrared regions by changing the Fermi energy and thickness of the graphene layer. Another exciting finding is that the use of a silver shell in the hollow bi-shell nanoparticles provides another LSPR peak besides that induced by the graphene shell. Both LSPRs of graphene and silver shells can be overlapped by changing the optical properties of graphene and/or the geometrical parameters of the silver shell. The resulting LSPR is characterized by a dominant absorption cross-section and a significant narrowband. In both proposed nanoshell designs, the properties of LSPRs are promising for use in various optical imaging and phototherapy applications.

Plasmon properties such as peak position, extinction cross-section and local electric field intensity are strongly dependent on excited, localized surface plasmon resonance (LSPR) modes. In non-spherical copper chalcogenide nanoparticles, assignment of the LSPR peaks to the corresponding oscillation modes has been controversial and requires experimental verification. We determined the in-plane LSPR mode of roxbyite Cu7S4 nanodisks from the plasmon coupling effect of nanodisks in solution. Compared with individual Cu7S4 nanodisks, self-assembled Cu7S4 nanodisk arrays in chloroform exhibited a blue-shifted LSPR peak with weaker optical density. This strongly suggests that the singular LSPR peak in the near-infrared region mainly originates from the in-plane oscillation mode. In addition, we demonstrate that the same LSPR peak can be readily tuned by controlling the number of disks in the array.

Hybrid nanostructures of plasmonic gold nanoparticles with a-C:H thin films

The extinction maximum of the localized surface plasmon resonance (LSPR) of noble metal nanoparticles is highly dependent upon the refractive index of the nanoparticles' surrounding environment. In this study, the effect that molecular resonances have on the intensity, LSPR peak width, and LSPR shift of the LSPR of Ag nanoparticles is monitored. By systematically tuning the LSPR extinction maxima of Ag nanoparticles versus molecular resonances, new phenomena are revealed. First, the LSPR peak shift induced by a resonant molecule varies with wavelength. In most instances, the trends in this data qualitatively track with the Kramer's-Kronig transformation of the molecular resonance spectrum; however, the magnitude of the response is severely underestimated. This was verified from both experimental data and theoretical calculations. Because this phenomenon is revealed to be electronic transition dependent, it is hypothesized that the coupling between the molecular and plasmon resonances is responsible for this wavelength dependent observation. These results will have implications in molecular enhanced LSPR sensing and in the understanding of surface-enhanced spectroscopy.

Localized surface plasmon resonance (LSPR) biosensors show great potential for practical/commercial use in clinical diagnosis, home healthcare, environmental analysis, and public healthcare. However, two main issues, that is, low refractometric sensitivity and low reproducibility (large-area uniformity and batch-to-batch consistency), hinder the extensive applications of LSPR biosensors. Therefore, plasmonic nanostructures with high sensitivity and excellent reproducibility are desirable for preparing reliable LSPR sensors. Herein, we have fabricated plasmonic nanopyramid arrays (NPAs) for several batches with reproducible morphology and optical properties by elastic soft lithography and metal thermal evaporation. NPAs of various metals (i.e., Al, Au, and Ag) were also prepared by thermal evaporation with the according metals. The transmission spectra of these NPAs showed several narrow LSPR peaks in the visible-infrared wavelength region. The refractometric sensitivities of the LSPR peaks were systematically studied, and high refractometric sensitivities of 774.0, 472.8, and 421.0 nm/RIU were achieved on Al, Au, and Ag NPAs, respectively. To demonstrate the potential of the NPAs for multiplex applications, we first applied this highly sensitive Al NPA biosensor to monitoring the process of proliferation of HeLa cancer cells, in situ and in real time. Then, we demonstrated that the Au NPA was able to identify the absorbed analytes on its surface through the surface-enhanced Raman scattering spectrum. In addition, the finite difference time domain simulations were performed to reveal the electromagnetic field enhancement on NPAs. Because of the properties of high sensitivity and excellent reproducibility of the metal NPA LSPR substrates, as well as the simplicity and cost efficiency of the fabrication method, our proposed work will accelerate the practical use of LSPR sensors.

Development of silver/gold nanocages onto indium tin oxide glass as a reagentless plasmonic mercury sensor

Gold nanostars (GNSs) have received considerable attention in surface-enhanced spectroscopies, catalysis, biosensing, photothermal therapy, and photovoltaics because of their unique optical properties arising from the anisotropic structure. GNSs typically consisting of a central core and several protruding tips are usually synthesized by a seed-mediated growth approach, but the growth mechanism and optical properties have yet to be fully understood. Here, we systematically investigate the seed-mediated growth process of GNSs to gain an insight into the growth mechanism and evolution of their optical and photothermal properties. By tailoring the core size, tip length and tip angle, the main localized surface plasmon resonance (LSPR) peak wavelength can be broadly tuned from the visible to near-infrared (NIR) region. Our observations show that the protruding tips grow rapidly away from the central core at the initial growth stage, leading to a red-shift of the main LSPR peak. The preferential deposition of gold atoms onto the gold core takes place at the later growth stage, gradually blue-shifting the main LSPR peak. GNSs exhibit a large molar extinction coefficient ranging from 4.0 × 108 M-1 cm-1 to 4.5 × 1010 M-1 cm-1, the log value of which correlates linearly with the main LSPR peak wavelength and accordingly allows for facile determination of the GNS concentration in a suspension. In addition, GNSs are excellent NIR photothermal materials with the LSPR-dependent photothermal conversion efficiency. The maximum photothermal conversion efficiency of GNSs occurs at a LSPR wavelength of 740 nm, blue-shifted from the incident laser wavelength. Our present work suggests that GNSs exhibit excellent optical and photothermal properties that can be optimized by tailoring the dimensional parameters.

The localized surface plasmon (LSP) resonances properties of periodic arrays of nanoholes in thin gold films are investigated by using the method of discrete dipole approximation (DDA). The surface plasmon polaritons (SPPs) play important roles in amplification or suppression of the LSP resonances in the film. The LSP-SPP coupling is affirmed based on the extinction spectra calculated by the DDA. The intensity of the LSP resonances can be controlled through changing the edge-to-edge separation distances between nanoholes, the number and the diameter of the nanoholes. The calculations also indicate that the LSP resonance peak decreases with increasing the thickness of the gold film.

Periodic hexagonal gold crystal spherical nanoparticle arrays with controllable size and periodicity are fabricated by physical vapor deposition and further heat treatment based on monolayer colloidal crystal template. The size and center-to-center spacing of nanoparticles (NPs) were manipulated conveniently by tuning the deposition thickness of Au film and the size of colloidal spheres of the template, respectively. The thickness range of deposited Au film dependent on the size of colloidal spheres was investigated comprehensively. Dewetting model was established and employed to analyze the whole process of the evolution from gold film to spherical nanoparticle with uniform size. Additionally, localized surface plasmon resonance (LSPR) responses of these Au nanoparticle arrays were systematically measured. It is found that the extinction properties are significantly influenced by the particle size and periodicity of arrays. With the increase of particle size, the LSPR peak shows a red shift due to the quantum size effect of the nanoscaled Au particle. Meanwhile, the diffraction peaks also show small red shift due to a slight increase of average refractive index of arrays. This is highly helpful to improve its practical applications for detecting biochemical molecules based on LSPR and diffraction peak sensing.

In this work, localized surface plasmon resonance (LSPR) sensing as applicable in the detection of Trenbolone acetate dopant is demonstrated. We show that the LSPR of the Trenbolone acetate/silver nanoparticle (Tren Ac/AgNPs) complex is sensitive to changes in the adsorbent concentration. The results show an average redshift of + 18 nm in the LSPR peak with variations in intensity and broadening behavior of the LSPR band of the Tren Ac/AgNPs complex. AgNPs were synthesized using laser ablation in liquid (LAL) technique with water as the solvent. UV–Vis spectroscopy was used for absorbance measurements and particle size and morphology were monitored using scanning electron microscopy (SEM). The aggregation behavior of the Tren Ac/AgNPs complex was monitored using energy-dispersive X-ray spectroscopy (EDS). Molecular Electrostatic Potential (MEP) and the HOMO–LUMO orbitals of the optimized Trenbolone acetate structure were obtained using Density Function Theory (DFT). The molecule was optimized at the B3LYP level of theory using the 6–311 basis set carried out using the Gaussian 09 software package. The results showed that O2− is Trenbolone acetate’s active site that would interact with Ag+ to form a complex that would influence the plasmon behavior. The results presented in this work demonstrate the feasibility of LSPR for anabolic androgenic steroid detection.

A work function (WF) centric theory is developed for the localized surface plasmon resonance (LSPR) energy (in the non-scattering regime) for ligand-capped metal nanoparticles (NPs) with atomic steps. Theoretical LSPR energy is the product of the electrochemical work function (EWF) and the attenuation factor . The semi-microscopic model for the EWF includes a curvature-dependent WF, crystallographic information through the step density (ns), partial charge of adsorption (δa), dipolar orientation, the packing density of the ligand (N0), and the number of adsorbing contacts (nL) of the capping ligand. is a function of electronic screening length (lTF) and attenuation length (led). decays exponentially with the ratio of plasmonic cloud depth (2lTF) to led. The LSPR peaks (λmax) of plasmonic metals (the same NP size) follow the reverse order of their EWF values. The LSPR absorption peak red-shifts with an increase in size (2r), ns, and N0, while blue-shifts with an increase in the number of adsorbing contacts of the capping ligand (like the citrate ion). Coinage metals, viz. Au, Ag, and Cu, exhibit size (2r < 50 nm)-dependent LSPR peaks in the visible spectrum: 420 nm ≲ λmax ≲ 520 nm, for nL = 1. Pt shows anomalous twin peaks, attributed to the distinct number of carboxylic groups of citrate capping on the metal: one for nL = 2, with size-dependent peaks in the visible spectrum: 430 nm ≲ λmax ≲ 454 nm and another for nL = 3, with peaks in the UV spectrum: 378 nm ≲ λmax ≲ 400 nm. Finally, theory shows agreement with the experimental data for citrate-capped Au and Au/Ag alloy NPs.

Metal nanoparticles (MNPs) have potential uses in biochemical sensing applications owing to their localised surface plasmon resonance (LSPR) characteristics. In practice, selective biochemical sensors based on LSPR are constructed by MNPs and selective receptors for specific biochemical molecules. This Letter studies the effects of receptor thickness on LSPR sensing properties experimentally and theoretically. Experimental results demonstrate that an increase in polymethyl methacrylate (PMMA) receptor thickness induces a red shift of LSPR spectrum. For a 42 nm PMMA receptor, the maximum extinction efficiency is more sensitive to the test chloroform vapour than the peak wavelength. This receptor thickness effect is confirmed by electrodynamics calculations: a relatively thin receptor layer will create high peak wavelength sensitivity and low extinction efficiency sensitivity. However, it is the opposite for a relatively thick receptor layer. The turning point between thick and thin is approximately 20 nm in this Letter. These insights can be used as guidelines in fabricating high-sensitive LSPR-based biochemical sensors.

Localized surface plasmon resonance (LSPR) excitation on single silver nanoring with nanoscale surface roughness

A dual colorimetric and fluorometric sensor based on N, P-CDs and shape transformation of AgNPrs for the determination of 6-mercaptopurine