Bragg-Scattered Surface Plasmon Microscopy: Theoretical Study

We present a new approach to surface plasmon microscopy with high refractive index sensitivity and spatial resolution that is not limited by the propagation length of surface plasmons. It is based on a nanostructured metallic sensor surface supporting Bragg-scattered surface plasmons. We show that these non-propagating surface plasmon modes are excellently suited for spatially resolved observations of refractive index variations on the sensor surface owing to their highly confined field profile perpendicular to as well as parallel to the metal interface. The presented theoretical study reveals that this approach enables reaching similar refractive index sensitivity as regular surface plasmon resonance (SPR) microscopy and offers the advantage of improved spatial resolution when observing dielectric features with lateral size <10???m for the wavelength around 800?nm and gold as the SPR-active metal. This paper demonstrates the potential of Bragg-scattered surface plasmon microscopy for high-throughput SPR biosensing with high-density microarrays.     

Theoretical Modeling of Average Force Acted on Nano Plasma Spheres in Presence of Radiation of Long Wavelength Point Source

Plasmonics - Using the solutions of field equation, due to the electromagnetic wave scattering phenomena from a nano plasma sphere(NPS), the inserted force on nano plasma sphere is simulated. For...     

Theoretical Study of Sensitivity and Localized Surface Plasmon Resonance of Ag-Dielectric Core-Shell Multi-layered Nanosphere

Localized surface plasmon resonances (LSPRs) of Ag-dielectric-Ag multi-layered nanoshell are studied by quasi-static approximation and plasmon hybridization theory. Absorption properties of multi-layered nanoshell with the silver core and nanoshell separated by a dielectric layer exhibit strong coupling between the core and nanoshell. The result shows absorption spectrum of LSPRS is influenced by the refractive index of surrounding medium, the dielectric constant of middle dielectric layer, the thickness of inner core radius and outer shell layer. LSPR shift of the longest wavelength \(\left |\omega _{-}^{-}\right >\) is red-shifted with increasing the inner core radius. It is interesting to find that longer wavelength \(\left |\omega _{-}^{+}\right >\) mode is mainly effected by the ratio constant of the surrounding medium refractive index ε ₄ to the middle layer dielectric constant ε ₂. \(\left |\omega _{-}^{+}\right >\) mode takes place a blue-shift with increasing inner core radius when ε ₂ > ε ₄, a red-shift when ε ₂ < ε ₄, and no-shifting when ε ₂ = ε ₄. However, the influence of dielectric layer radius to \(\left |\omega _{-}^{+}\right >\) mode shows the different property as that of increasing the inner core radius. The underlying mechanisms are analyzed with the plasmon hybridization theory and the distribution of induced charge interaction between the inner core and outer shell. In addition, the influence of core radius, middle dielectric layer radius and outer shell radius to sensitivity of Ag-dielectric-Ag multi-layered nanoshell are also reported, a higher sensitivity could be gotten by adjusting geometrical parameters. Our theoretical study could give an easy way to analyze properties of the core-shell nanosphere based on plasmon hybridization theory and the induced charge interaction, and usefully broaden the applications in nano-optics.     

Theoretical Study of the Local Surface Plasmon Resonance Properties of Silver Nanosphere Clusters

The local surface plasmon resonance properties in systems consisting of silver nanosphere clusters are studied by Green’s function. The extinction, absorption, and scattering efficiencies band of two, three, and more silver nanospheres clusters are discussed in detail. The clusters show new types of the local surface plasmon resonances compared with single silver nanosphere. Our results suggest that the resonances depend strongly on individual particles’ characteristics such as their shapes, gap distances, directions and polarizations of incident light waves, and the number of clusters. The spectrum shows that equilateral triangle nanospheres has a good absorption peak, while the better red-shifted with three aligned nanospheres. In addition, the distributions of electric field intensity for three and four touched silver nanospheres are also investigated. The study is useful to broaden the application scope of Raman spectroscopy and nanooptics.     

Experimental Study on Localized Surface Plasmon Mode Hybridization in the Near and Mid Infrared

We investigate plasmon excitations within a regular grating of double-layered gold/insulator nanoparticles in the infrared and visible spectral region. Provided a flat gold film as substrate, strong coupling between the localized surface plasmon modes and their image-like excitations in the metal is observed. The interaction results in a strong red shift of the plasmon mode as well as the splitting of the modes into levels of different angular momenta, often referred to as plasmon hybridization. The diameters of the nanoparticles are designed in a way that the splitting of the resonances occurs in the spectral region between 0.1 and 1 eV, thus being accessible using an infrared microscope. Moreover, we investigated the infrared absorption signal of gratings that contain two differently sized nanoparticles. The interaction between two autonomous localized surface plasmon excitations is investigated by analyzing their crossing behavior. In contrast to the interaction between localized surface plasmons and propagating plasmon excitations which results in pronounced anticrossing, the presented structures show no interaction between two autonomous localized surface plasmons. Finally, plasmon excitations of the nanostructured surfaces in the visible spectral region are demonstrated through photographs acquired at three different illumination angles. The change in color of the gratings demonstrates the complex interaction between propagating and localized surface plasmon modes.     

Strong Suppression of Surface Plasmon Radiation Damping Rate in Noble Metal Nanoshells

Radiation damping of surface plasmon oscillations in metallic nanoparticles is proportional to their volume. For relatively large particles, this canal dominates the other mechanisms of relaxation and becomes the main limiting factor for spectral sensitivity of nanoparticles. In this communication, we consider metallic nanoshell with the dielectric core and calculate the radiation damping rate of surface plasmon oscillations, depending on the geometry and dielectric constants of the surrounding environment and the core. It is shown that surface plasmon radiation damping in nanoshell is suppressed by several orders of magnitude as compared to the solid particle of the same outer radius. This effect is conditioned by strong redshift of surface plasmon frequencies with the decrease of shell thickness. It is also demonstrated that the radiation damping rate of core–shell particle is highly sensitive with respect to the refractive index of surrounding media.     

Theoretical Assessment of Localized Surface Plasmon Resonance Properties of Au-Interlayer-Ag Multilayered Nanoshells

Plasmonics - The localized surface plasmon resonance (LSPR) properties of Au-interlayer-Ag multilayered nanoshells are studied by discrete dipole approximation (DDA) and plasmon hybridization...     

Theoretical Studies of Tunable Localized Surface Plasmon Resonance of Gold-Dielectric Multilayered Nanoshells

Tunable properties of localized surface plasmon resonances (LSPR) of gold-dielectric multilayered nanoshells are studied by quasi-static theory and plasmon hybridization theory. Multilayered nanoshells with the gold core and nanoshell separated by a spacer layer exhibit strong coupling between the core and nanoshell plasmon resonance modes. It is found that the absorption spectra characteristics of LSPR are sensitive to multiple parameters including the surrounding medium refractive index, the dielectric constant of spacer layer, the radius of inner core gold sphere, outer shell layer thickness, and their coupling strength. The results show that LSPR is mainly influenced by the ratio of spacer layer dielectric constant ε ₂ to surrounding medium dielectric constant ε ₄. Absorption spectrum of \(\left |\omega _{-}^{+}\right \rangle \) mode is red-shifted with increasing core radius when ε ₂ > ε ₄. It is surprising to find that LSPR is blue-shifted with increasing core radius when ε ₂ < ε ₄, and no shift when ε ₂ = ε ₄. These interesting contrary shifts of \(\left |\omega _{-}^{+}\right \rangle \) mode with different ratios ε ₂/ε ₄ are well analysed with plasmon hybridization theory and the distributions of induced charges interaction between the inner core and outer shell. In addition, for the sake of clarity, the distributions of electric filed intensity at their plasmon resonance wavelengths are also calculated. This work may provide an alternative approach to analyse property of the core-shell nanoshell particles based on plasmon hybridization theory and the induced charge interaction.     

Imaging of Surfaces by Concurrent Surface Plasmon Resonance and Surface Plasmon Resonance-Enhanced Fluorescence

Surface plasmon resonance imaging and surface plasmon induced fluorescent are sensitive tools for surface analysis. However, existing instruments in this area have provided limited capability for concurrent detection, and may be large and expensive. We demonstrate a highly cost-effective system capable of concurrent surface plasmon resonance microscopy (SPRM) and surface plasmon resonance-enhanced fluorescence (SPRF) imaging, allowing for simultaneous monitoring of reflectivity and fluorescence from discrete spatial regions. The instrument allows for high performance imaging and quantitative measurements with surface plasmon resonance, and surface plasmon induced fluorescence, with inexpensive off-the-shelf components.     

Nonlocal Effects on Optical Gradient Force from Coupled Surface Plasmon Polaritons in Wire Medium Waveguides

Plasmonics - We analytically study optical gradient forces from the mutual coupling between surface plasmon polariton (SPP) modes at the interfaces of two wire medium metamaterial waveguides...     

Robust and Tunable One-Way Magnetic Surface Plasmon Waveguide: An Experimental Demonstration

We have demonstrated experimentally a one-way magnetic surface plasmon (MSP) electromagnetic (EM) waveguide in the microwave range based on the magnetic photonic crystals (MPCs). The waveguide exhibits asymmetric transmission of EM waves in the frequency range near the MSP resonance for an MPC, such that a significant one-way propagation can be observed in the channel between the two MPC slabs, each in an external static magnetic field (ESMF) of opposite directions. The one-way waveguide is not only immune to interstitial metal defects but also robust against the disorder of rod position. Furthermore, its working frequency can be flexibly tuned by an ESMF, which makes it more favorable for the design of EM devices. The physics is related to the broken time-reversal symmetry of the MSP band states and the excitation of a giant circulation of the energy flow, similar to the case in the quantized Hall effect.     

Theoretical Differential Phase Analysis for Characterization of Aqueous Solution Using Surface Plasmon Resonance

Surface plasmon resonance (SPR)-based differential phase analysis has been presented. Real as well as complex plane analysis of resonance parameters have been undertaken for the optimum selection of metal thicknesses in a bimetallic SPR configuration working under both angular and spectral regime. Theoretically, we can characterize the aqueous solution in terms of this differential phase variation due to the variation of sample parameters such as concentration and temperature. In this respect, two case studies, namely, concentration of hemoglobin in human blood and sensing of temperature of water have been demonstrated and proposed theoretically. By monitoring the change of differential phase, proposed approach leads to a very sensitive measurement of concentration and temperature.     

Nanostructuring of Continuous Gold Film by Laser Radiation Under Surface Plasmon Polariton Resonance Conditions

The physical mechanisms of metallic nanoparticles formation by laser technology were studied. The system air/Au film/glass was irradiated by laser at the conditions of surface plasmon resonance. A surface electromagnetic wave was excited in Kretchmann configuration by the fundamental and second harmonics of the Q-switched YAG/Nd⁺³ laser with pulse power density close to the threshold of melting. Nanostructuring of Au film was observed only for the second harmonic (λ = 0.532 μm) irradiation at the surface plasmon polariton resonance (SPR) conditions. Estimations were done using the interference model of the differently directed plasmon polariton waves excited by a surface electromagnetic wave on the metal surface. It was shown that a regular pattern of locally heated spots can be formed in a metallic film by pulsed laser irradiation. The spatial distribution of this pattern is close to the period of interference. The observed effect of laser nanofragmentation is explained by the self-organization of plasmon polariton subsystem in the process of Au nanoparticles formation at high laser intensity levels. These methods open new possibilities for nanostructured surfaces formation utilizing simple self-organization processes.     

Surface Plasmon Coupling Effect of Gold Nanoparticles with Different Shape and Size on Conventional Surface Plasmon Resonance Signal

The labeling strategy with gold nanoparticles for the conventional surface plasmon resonance (SPR) signal enhancement has been frequently used for the sensitive determination of small molecules binding to its interaction partners. However, the influence of gold nanoparticles with different size and shape on SPR signal is not known. In this paper, three kinds of gold nanoparticles, namely nanorods, nanospheres, and nanooctahedrons with different size, were prepared and used to investigate their effects on the conventional SPR signal at a fixed excitation wavelength 670 nm. It was found that the SPR signal (i.e., resonant angle shift) was varied with the shapes and sizes of gold nanoparticles in suspension at a fixed concentration due to their different plasmon absorbance bands. For gold nanorods with different longitudinal absorbance bands, three conventional SPR signal regions could be clearly observed when the gold nanorod suspensions were separately introduced onto the SPR sensor chip surface. One region was the longitudinal absorbance bands coinciding with or close to the SPR excitation wavelength that suppressed the SPR angle shift. The second region was the longitudinal absorbance bands at 624 to 639 and 728 to 763 nm that produced a moderate increase on the SPR resonant angle shift. The third region was found for the longitudinal absorbance bands from 700 to 726 nm that resulted in a remarkable increase in the SPR angle shift responses. This phenomenon can be explained on the basis of calculation of the correlation of SPR angle shift response with the gold nanorod longitudinal absorbance bands. For nanospheres and nanooctahedrons, the SPR angle shift responses were found to be particle shape and size dependent in a simple way with a sustaining increase when the sizes of the nanoparticles were increased. Consequently, a guideline for choosing gold nanoparticles as tags is suggested for the SPR determination of small molecules with binding to the immobilized interaction partners.     

Ultrasensitive Deep-Ultraviolet Surface Plasmon Resonance Sensors Using Aluminum-Graphene Metasurface: a Theoretical Insight

Plasmonics - This study investigates a versatile deep-ultraviolet (DUV) surface plasmon resonance (SPR) sensor by integrating a few graphene layers into low-cost aluminum (Al) thin film. The...     

Dispersion and Damping of Gold Surface Plasmon

High-resolution electron energy loss spectroscopy was used to investigate the surface plasmon dispersion in (111)-oriented Au films grown on Cu(111). The measured dispersion of the plasmon mode was positive, as found for Ag. The centroid of the induced charge associated to the plasmon field lies well inside the jellium edge. The damping relation of the Au surface plasmon presented a critical wave vector of 0.11 Å^?1. For higher values of the parallel momentum transfer, the line width of Au surface plasmon considerably increased as a consequence of the opening of a new decay channel via single-particle transitions.     

Coupling Behaviors of Surface Plasmon Polariton and Localized Surface Plasmon with an InGaN/GaN Quantum Well

Plasmonics - Surface plasmon (SP) coupling behaviors of an InGaN/GaN quantum well (QW) with surface plasmon polariton (SPP) induced on a smooth Ag-film/GaN interface and localized surface plasmon...     

Theoretical Considerations on the Responses of Gold-Deposited Surface Plasmon Resonance-Based Glass Rod Sensors Using a Three-Layer Fresnel Equation

The response curves of gold (Au)-deposited surface plasmon resonance-based glass rod sensors were calculated using a three-layer Fresnel equation while considering various parameters for the sensor system calculations. Au films with thicknesses of 30, 45, and 70 nm were deposited on half of the surfaces of the glass rods, which were 2 mm in diameter, with a deposition length of 100 mm. Sensor elements with Au film thicknesses of 45 nm on glass rods with diameters of 1 and 4 mm and with deposition lengths of 10, 20, and 50 mm were also prepared. The sensor system consists of a light-emitting diode (LED) with a wavelength of 654 nm as the light source with a mini-spectrometer as the detector. The LED intensity distribution, the range of the angle of incidence of light into the sensor element, and the thickness distributions of the Au films deposited on the glass rods were considered to be the important parameters for the calculations. The minimum positions of all the theoretical response curves agreed well with those of the experimental response curves within the limits of the experimental and theoretical uncertainties. Most of the overall response characteristics of the theoretical curves agreed well with those of the experimental curves within the limits of both types of uncertainty. It was found that the thickness distribution of the deposited Au film in the cross-sectional direction dominates the sensor response and thus is the most important parameter for calculation of the sensor properties. The agreements between the experimental and theoretical response curves indicate both the potential and the usefulness of the sensor performance estimation process based on the three-layer Fresnel equation.     

Molecular Study of P-Glycoprotein in Multidrug Resistance Using Surface Plasmon Resonance

P-Glycoprotein is an integral membrane protein which mediates the energy-dependent efflux of various antitumor agents from multidrug-resistant cancer cells. Surface plasmon resonance was used for the detection of P-glycoprotein after solubilization from drug-resistant and drug-sensitive Chinese hamster ovary cells and for the analysis of its interaction with cyclosporin A, a competitive inhibitor of drug efflux. Detection of P-glycoprotein relied on its binding to the monoclonal antibody C219 which was immobilized on a sensor chip. Binding of Zwittergent 3-14-solubilized P-glycoprotein to the antibody was concentration-dependent and reflected the relative abundance of P-glycoprotein in both cell lines. It was abolished when C219 was omitted or replaced by a rabbit anti-mouse IgG antibody and considerably reduced after precipitation of P-glycoprotein with wheat germ agglutinin. Preincubation of solubilized proteins with cyclosporin A increased the amount of protein bound to the antibody by approximately 30%. These results indicate that surface plasmon resonance is well suited to the detection of P-glycoprotein from biological samples and shows promise as a tool for the study of its interaction with different drugs.