Plasmon Modes Management

A new plasmonic structure based on bimetallic layer is proposed. We analyze the structure and show that bimetallic film plays a crucial role in the management of surface plasmons. The roll of the buffer is discussed, as well. Up to three surface plasmons can be excited simultaneously in the structure. Two of plasmons can be used for two-plasmon spectroscopy. The third plasmon can be used for controlling the temperature of the structure.     

Tailoring Plasmon Lifetime in Suspended Nanoantenna Arrays for High-Performance Plasmon Sensing

We demonstrate significantly longer plasmon lifetime and stronger electric field enhancement by lifting the nanoantenna arrays above the substrate by dielectric nanopillars. The role of the pillar is to offer a more homogeneous dielectric background allowing stronger diffraction coupling among plasmonic nanoantennas leading to a Fanolike asymmetric lineshape. It is found that the electric fields around the nanoantennas can be greatly enhanced when the Fanolike resonance is excited, and a 4.2 times enhancement is achieved compared with the pure resonance in individual nanoantennas. Furthermore, only a collective surface mode with its electric fields of the same direction as the induced electric moment in the nanoantennas could mediate the excitation of such a Fanolike resonance. More importantly, the sensitivity and the figure of merit (FOM) of this plasmonic structure can reach as high as 900 nm/RIU and 53, respectively. Our study offers a new, simple, and efficient way to design the plasmonic systems with desired electric field enhancement and spectral lineshape for different applications.     

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.     

Nano-gap-Enhanced Surface Plasmon Resonance Sensors

This paper analyzes how dual-mode surface plasmon resonance sensors can be further improved if one were to introduce small (∼20 nm) gaps in the film surface. First, a figure of merit, the sensor’s limit of detection (LOD), is defined in order to optimize the design of the nano-gap sensor. Secondly, the LOD of this design is compared with that of an optimized planar dual-mode design. Through this analysis, it is shown that the LOD of the planar sensor can be improved upon by around a factor of 7 when compared with the nano-gap-enhanced design. Furthermore, with the nano-gap design, the lower wavelength plasmon mode demonstrates remarkably improved selectivity when compared with the conventional sensor. In order to explain these results, the dispersion of each plasmon mode along with the electromagnetic field profiles are modeled and analyzed.     

Surface Plasmon Resonances of Clustered Nanoparticles

Linear clusters made by tightly connecting two or more metallic nanoparticles have new types of surface plasmon resonances as compared with isolated nanoparticles. These new resonances are sensitive to the size of the junction and to the number of interconnected particles and are described by eigenmodes of a boundary integral equation. This formulation allows effective separation of geometric and shape contribution from electric properties of the constituents. Results for particles covered by a thin shell are also provided highlighting ultrasensitive sensing applications. The present analysis sheds a new light on the interpretation of recent experiments.     

Wavelength-Ratiometric Plasmon Light Scattering-Based Immunoassays

The application of a wavelength-ratiometric plasmon light scattering technique to immunoassays is demonstrated. A model immunoassay for anti-immunoglobulin G (IgG), constructed in gold colloid-modified high-throughput screening wells, was monitored by the changes in the intensity of scattered light (with transmitted light) from gold colloids as a result of antibody–antibody interactions. The quantitative determination of anti-IgG was undertaken by measuring the ratio of intensity of scattered light at both 590 and 500 nm. A white light-emitting diode (LED) and a fiber optic coupled fluorometer was used as an excitation source and the detection system, respectively. The visual confirmation of the quantitative nature of the measurement technique was done by digital photography. A lower detection limit of 0.05 μg/mL for anti-IgG was determined. The wavelength-ratiometric plasmon light scattering technique offers several advantages: (1) light at >500 nm can be used for reduced biological autofluorescence; (2) due to the ratiometric nature of these measurements, the fluctuations in the excitation or ambient light do not perturb the measured signal; and (3) with the addition of automated detection systems, multiple samples in a high-throughput format can potentially be assessed quickly and more efficiently.     

Multiple-Beam Surface Plasmon Holographic Nanolithography

Multiple-beam surface plasmon holographic nanolithography based on a hemispherical prism coupling configuration is numerically studied in this paper. The proposed configuration is systematically analyzed and optimized for the purpose of achieving five different two-dimensional Bravais lattices by means of adjusting the spatial distribution of three incident beams properly. Furthermore, it is shown that the variation in the relative phase between incident beams can give rise to rich periodic patterns when overlapping more than three beams for surface plasmon holographic nanolithography.     

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...     

Spectral Characteristics of Near-Infrared Surface Plasmon Resonance

Intrinsic properties of surface plasmons (SPs) excited with Kretschmann configuration were analyzed as a function of wavelength, including the propagation length, the penetration depth, the Goos–Hänchen (GH) shift, and the field enhancement. The calculated results indicate that there exists a critical thickness (t _cr) of the gold layer and that the maximum GH shift occurring exactly at the SP resonance wavelength (λ _R) rapidly varies from positive to negative with changing of the gold layer thickness from t?<?t _cr to t?>?t _cr. The maximum field enhancement happens not at λ _R but at a wavelength smaller than λ _R due to the phase retardation between the transmitted and reflected light. Simulations also reveal that a broadband collimated near-infrared beam can simultaneously excite two SPs with different responses to a refractive index (RI) change: the shorter-wavelength SP able to make a small redshift and the longer-wavelength SP capable of yielding a large blueshift. Only the shorter-wavelength SP was experimentally observed and its RI sensitivity was measured to increase from 3,539 nm/RIU at λ _R?=?707.6 nm to 57,143 nm/RIU at λ _R?=?1,398 nm. The SP at λ _R?=?1,013 nm moved to λ _R?=?1,029 nm in response to the saturation adsorption of bovine serum albumin, and the corresponding surface coverage was determined to be Γ?=?1.565 ng/mm² based on a quasilinear dependence of Γ on the resonance wavelength shift (?λ _R) deduced theoretically. Butyrylcholinesterase adsorption from a dilute solution of 10 nM protein in phosphate buffer solution leads to a redshift of ?λ _R?=?10 nm, corresponding to Γ?≈?0.97 ng/mm².     

Liquid Crystal-Based Surface Plasmon Resonance Biosensor

Plasmonics - Surface plasmon resonance has many applications in designing biosensors. In this paper, an easy fabrication liquid crystal-based surface plasmon resonance (LC-SPR) biosensor is...     

Extraction of the 3D Plasmon Field

We present the novel approach to investigate properties of the 3D plasmon excited on a metal sphere. The exact plasmon field extracted from the scattered field given by Mie theory allows for a new interpretation of the 3D plasmon by four short-range-like plasmons excited and rotating simultaneously around the sphere.     

Surface Plasmon Dynamics of High-Aspect-Ratio Gold Nanorods

Ultrafast transient absorption studies are reported for high-aspect-ratio gold nanorods that were fabricated by electrochemical deposition in polycarbonate templates. The nanorods are 60 nm in diameter with distribution of lengths of up to 6 μm. The average aspect ratio was ∼50, resulting in a longitudinal surface plasmon resonance (SPR_L) band in the mid-IR, as well as a transverse (SPR_T) band in the visible. The rods were excited at 400 nm and probed at a range of wavelengths from the visible to the mid-IR to interrogate both SPR bands. The dynamics observed, including the electron–phonon coupling time and coherent acoustic breathing mode oscillations, closely resemble those previously reported for gold spherical nanoparticles and smaller-aspect-ratio nanorods. The electron–phonon coupling time was similarly determined to be 3.3 ± 0.2 ps for both of the SPR bands. Also, oscillations with a 32-ps period were observed for probing near the SPR_T band in the visible region due to impulsive coherent excitation of the acoustic breathing mode, which are consistent with the 60-nm diameter of the nanorods determined by scanning electron microscopy. The results demonstrate that the dynamics for long gold nanorods are similar to those for smaller nanoparticles. Gerald M. Sando is a NRL-ASEE Research Associate     

Plasmon Resonances in V-Shaped Gold Nanostructures

Using numerical simulations, we examine the change in plasmon resonance behavior in gold nanorod structures that have a V shape. The reduction in symmetry compared to linear rods causes two different longitudinal-type resonances to appear in a single structure, and the relative intensity and hybridization of these can be controlled by varying the angle of the arms of the ??V.?? The resonances may also be selectively excited by controlling the polarization of the incident light, thereby providing a convenient way to control a nanoscale optical electric field using far-field parameters. For example, the wavelength at which a strong resonance occurs in the V-shaped structures studied can be switched between 630 and 900?nm by a 90° rotation of the polarization of the incident light. Due to the symmetry of the targets, there will be three types of special near-field location; a location at which the electric field intensity is enhanced by either resonance, a location at which the electric field intensity is enhanced by the 630?nm resonance but not by the 890?nm resonance, and a location at which the electric field intensity is enhanced by the 890?nm resonance but not by the 630?nm one.     

Plasmon resonant particles for biological detection

Several recent advances in the optical observation, fabrication, and bioconjugation of nanometer-sized gold or silver colloids have produced a robust new class of label. These plasmon resonant particle (PRP) conjugates have several important advantages: they are ultra-bright, so the light scattered from the individual particles can be viewed using a simple optical microscope system with a white light illumination source; they do not photo-bleach; PRPs can be prepared that preferentially scatter light of a chosen color; and it is possible to prepare bioconjugated PRPs that are stable in solution. These properties, and the automation of PRP identification, discrimination, and counting, have enabled the development of ultrasensitive, multicolor, and multiplex applications in the life science field.     

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.     

Aluminum-Based Deep-Ultraviolet Surface Plasmon Resonance Sensor

Plasmonics - An aluminum-based deep-ultraviolet surface plasmon resonance (DUV-SPR) sensor is promising for biological applications. Design aspects of a DUV-SPR sensor are here considered by using...     

Localized Surface Plasmon Enhanced Organic Light-Emitting Diodes

Current work demonstrates enhanced efficiencies in organic light-emitting diodes by using the localized surface plasmons originated from Au nanoclusters deposited using thermal evaporation technique. The effect of localized surface plasmons on organic emitter was studied using UV–vis absorption spectra, steady state and time-resolved photoluminescence spectra. These studies have revealed that the optical properties like absorption, emission have been greatly modified by the localized surface plasmon. These effects were found to be dependent on the distance between the emitter and Au layer. Further, efficiencies of the OLEDs were also found to be dependent on this distance.     

Development of Localized Surface Plasmon Resonance-Based Point-of-Care System

Plasmonics - This paper describes our point-of-care system development based on localized surface plasmon resonance (LSPR). Although LSPR has been a hot research area for a few decades, there are...