Electromagnetically Induced Transparency and Sharp Asymmetric Fano Line Shapes in All-Dielectric Nanodimer

Low-loss electromagnetically induced transparency (EIT) and asymmetric Fano line shapes are investigated in a simple planar silicon dimer resonator. The EIT and Fano effects emerge due to near-field coupling of the modes supported by both the nanoparticles in a dimer structure. Different configurations of the dimer nanostructure are analyzed, which provide distinct EIT and Fano resonances. Furthermore, the tunability of EIT and Fano resonant modes are incorporated by changing the structural parameters. It is also found that the dimer resonator exhibits high Q factor and large electromagnetic field enhancement at Fano resonance and EIT window due to extremely low absorption loss. Such values and narrow resonances are supposed to be useful highly sensitive sensors and slow-light applications.     

Optimization of immunolabeled plasmonic nanoparticles for cell surface receptor analysis

Noble metal nanoparticles hold great potential as optical contrast agents due to a unique feature, known as the plasmon resonance, which produces enhanced scattering and absorption at specific frequencies. The plasmon resonance also provides a spectral tunability that is not often found in organic fluorophores or other labeling methods. The ability to functionalize these nanoparticles with antibodies has led to their development as contrast agents for molecular optical imaging. In this review article, we present methods for optimizing the spectral agility of these labels. We discuss synthesis of gold nanorods, a plasmonic nanoparticle in which the plasmonic resonance can be tuned during synthesis to provide imaging within the spectral window commonly utilized in biomedical applications. We describe recent advances in our group to functionalize gold and silver nanoparticles using distinct antibodies, including EGFR, HER-2 and IGF-1, selected for their relevance to tumor imaging. Finally, we present characterization of these nanoparticle labels to verify their spectral properties and molecular specificity.     

Plasmonic Behaviors of Two-Dimensional Ag/SiO2 Nanocomposite Gratings: Roles of Gap Diffraction and Localized Surface Plasmon Resonance Absorption

Two-dimensional Ag/SiO₂ nanocomposite gratings of 400 and 600 nm in grating constant are fabricated by etching the SiO₂ slabs implanted with Ag ions, and their plasmonic extinction, absorption, and reflection behaviors are investigated. Our results indicate that no scattering light fields can exist near the localized surface plasmon (LSP) resonance wavelength (about 405 nm) of Ag nanoparticles (NPs) due to the intense LSP resonance absorption. Especially, when the gaps between nanocomposite veins have a width close in value to the LSP resonance wavelength of Ag NPs, the local light fields in the grating plane can be slightly enhanced due to an in-phase addition of the incident light fields and the diffractive light fields induced by the gap diffraction, leading to a slight red shift of LSP resonance mode of Ag NPs. Moreover, in the LSP resonance absorption region, although the grating diffraction can still occur, the diffractive light fields are extremely weak, and thus, the local light fields in the grating plane cannot be modified by coherently adding these extremely weak diffractive light fields to the incident light fields. As a result, the LSP resonance mode of Ag NPs will keep its position unchanged even though the grating constant is set to make the first grating order rightly change from evanescent to radiative character.

     

Study of Broadband Tunable Properties of Surface Plasmon Resonances of Noble Metal Nanoparticles Using Mie Scattering Theory: Plasmonic Perovskite Interaction

We suggest semi-analytical approach to study the optical properties of noble metal nanoparticles and their interaction to the perovskite material (methyl ammonia lead halide: CH₃NH₃PbI₃). Metal nanoparticles embedded in perovskite matrix exhibits broadband surface plasmon resonances, and the tunability of these plasmonic resonances is highly sensitive to particle size. The calculation of optical cross section have been done using Mie scattering theory which is applicable to arbitrary size and spherical-shape metal nanoparticles. We have taken five different radii ranging from 15 to 100 nm to understand the plasmonic resonances and its spectral width in the wavelength range 300 to 800 nm. Out of these noble metal nanoparticles, silver have highest scattering efficiency nearly of the order of 18 for the case of 15 nm radii at resonance wavelength 613 nm. Our finding reveals a new concept to understand the applications of plasmonic resonances in order to enhance the photon absorption inside the thin film of perovskite.     

Shape-Controlled Synthesis of Silver Nanoparticles for Plasmonic and Sensing Applications

The localized surface plasmon resonance of a silver nanoparticle is responsible for its ability to strongly absorb and scatter light at specific wavelengths. The absorption and scattering spectra (i.e., plots of cross sections as a function of wavelength) of a particle can be predicted using Mie theory (for a spherical particle) or the discrete dipole approximation method (for particles in arbitrary shapes). In this review, we briefly discuss the calculated spectra for silver nanoparticles with different shapes and the synthetic methods available to produce these nanoparticles. As validated in recent studies, there is good agreement between the theoretically calculated and the experimentally measured spectra. We conclude with a discussion of new plasmonic and sensing applications enabled by the shape-controlled nanoparticles.     

Surface-enhanced resonance Raman spectroscopy of porphyrin and metalloporphyrin species in systems with Ag nanoparticles and their assemblies

The advantages of systems with Ag nanoparticles and their assemblies for surface-enhanced resonance Raman scattering (SERRS) spectral investigation, detection and determination of porphyrin species are demonstrated. SERRS spectral detection limits of the testing porphyrin species (including porphyrin aggregates) in these systems are shown to be, on average, 10(2)-10(3) lower than detection limits by resonance Raman scattering (RRS). Systems with Ag nanoparticles modified by anionic organosulfur spacers enable us to obtain SERRS spectra of unperturbed cationic porphyrin species. In the case of thiopheneacetate-modified Ag particles prepared by laser ablation, no negative effect of the spacer on the spectral detection limit of the porphyrin was observed. Systems with isolated Ag nanoparticles allow for obtaining SERRS spectra of porphyrin species upon excitation into the Soret electronic absorption band which leads to at least a 10-fold decrease in the detection limit.     

Fitness Landscapes for Effects of Shape on Chemotaxis and Other Behaviors of Bacteria

Data on the shapes of 218 genera of free-floating or free-swimming bacteria reveal groupings around spherical shapes and around rod-like shapes of axial ratio about 3. Motile genera are less likely to be spherical and have larger axial ratios than nonmotile genera. The effects of shape on seven possible components of biological fitness were determined, and actual fitness landscapes in phenotype space are presented. Ellipsoidal shapes were used as models, since their hydrodynamic drag coefficients can be rigorously calculated in the world of low Reynolds number, where bacteria live. Comparing various shapes of the same volume, and assuming that departures from spherical have a cost that varies with the minimum radius of curvature, led to the following conclusions. Spherical shapes have the largest random dispersal by Brownian motion. Increased surface area occurs in oblate ellipsoids (disk-like), which rarely occur. Elongation into prolate ellipsoids (rod-like) reduces sinking speed, and this may explain why some nonmotile genera are rod-like. Elongation also favors swimming efficiency (to a limited extent) and the ability to detect stimulus gradients by any of three mechanisms. By far the largest effect (several hundred-fold) is on temporal detection of stimulus gradients, and this explains why rod-like shapes and this mechanism of chemotaxis are common.     

Geometry for Maximizing Localized Surface Plasmon Resonance of Au Nanorings with Random Orientations

The reduction of average extinction cross section of a localized surface plasmon (LSP) resonance mode under the random orientation condition of Au nanoring (NRI) distribution is first numerically demonstrated. The reduction range depends on the geometry symmetry property of the electron oscillation axis in the LSP resonance mode. Then, by increasing the ring height, an optimized Au NRI geometry is designed to make the resonance wavelengths of its cross-ring dipole mode and axial dipole mode the same. In such an Au NRI, a few higher-order axial LSP modes are discovered. Also, under the condition of random orientation distribution, the ranges of extinction, scattering, and absorption cross section reductions from the corresponding maximum levels of optimized excitations are significantly decreased, when compared with the counterparts of the Au NRIs of a smaller ring height.     

Spectral Tunability and Selectivity Based on Multiple Resonance Modes in End-Coupled Sectorial-Ring Cavity Waveguide

A plasmonic nanodevice in end-coupled sectorial-ring cavity waveguide is reported, and the spectral characteristic of the novel system is studied. It is built with sectorial-ring cavity resonator end-coupled to plasmonic waveguide, and  this resonator is an oversize central angle (θ), alterable symmetry plane angle (ϕ), and fixed radius and gap, which has the advantages of forming split-ring-like, realizing asymmetrical cavity, and achieving spectral tunability and selectivity. The two-dimensional simulation indicates that the extra noninteger and traditional integer resonance modes are excited in the novel system, and the noninteger resonance modes are not achievable for the circular-ring cavity waveguide. It displays that these resonance modes of the novel system are drastically affected by changing the position of ϕ, which has different changes on maximum transmittances but is almost unchanged on resonance wavelengths. Importantly, the multiple resonance modes are highly sensitive to ϕ, and the proper modes are significantly enhanced, weakened, excited, or disappeared. It also displays that these resonance modes of the novel system are efficiently affected by changing the size of θ, which has similar and different influences on resonance wavelengths and maximum transmittances. This work shows that the method helps in designing accurately the transmission spectrum with prospective modes in nanophotonics, and the structure facilitates for realization of tunable and selective multichannel nanofilter or nanosensor in integration.

     

Numerical Simulation of Broadband Scattering by Coated and Noncoated Metal Nanostructures Using Discrete Dipole Approximation Method

We suggest numerical method to study the optical response of metal nanostructures. The analysis of optical properties such as scattering and absorption by coated and noncoated nanogeometry has been done using discrete dipole approximation (DDA) method. The core-shell nanogeometry supports surface plasmon resonances, which are highly tunable from 400 to 1100 nm. The tunability of surface plasmon resonance (SPR) highly depends on the structural anisotropy and chosen core-shell material. Further, we have observed that aspect ratio is one of the key parameter to decide the nature and position of the plasmonic peaks and magnitude of optical cross section. We have also shown that coated nanospheroid is a more appropriate geometry as compared to coated nanosphere and noncoated nanospheroid in terms of wide tunability of surface plasmon resonance. The wide tunability in SPR is observed for the effective radii 90 nm core-shell (Au@SiO₂) nanospheroid with aspect ratio 0.1.     

InGaN/GaN MQW Photoluminescence Enhancement by Localized Surface Plasmon Resonance on Isolated Ag Nanoparticles

Spectroscopic study of photoluminescence (PL) enhancement due to the coupling of the light emitters in InGaN/GaN multiple quantum wells (MQWs) with the localized surface plasmon (LSP) resonance on silver (Ag) nanoparticles (NPs) is performed using the confocal microscopy and scanning near-field optical microscopy (SNOM) techniques. The paper is focused on revealing the emission enhancement due to coupling with a single metal nanoparticle. The enhancement is confirmed by time-resolved study of differential transmission (DT). The enhancement suppression caused by potential fluctuations due to the variations of indium content and quantum well (QW) width is also studied. A strong photoexcitation intensity dependence of the emission enhancement due to spectral runaway of the MQW emission from the resonance as carrier density increases is observed both in spatially integrated spectra and in the vicinity of a single nanoparticle.     

Tuning Plasmon Resonances for Light Coupling into Silicon: a “Rule of Thumb” for Experimental Design

For Si thin-film solar cells to become efficient, schemes to increase the optical absorption in the films are necessary. Scattering of light using plasmonic resonances in metal nanoparticles has been suggested as a feasible route. When placed on a dielectric layer on the front of a solar cell, such metal nanoparticles can scatter a large fraction of the incident light into the solar cell at the resonance wavelength, and hence increase the light collection. However, many related effects may lead to a reduction in photocurrent. Thus, nanoparticle plasmon resonances must be optimized in order to improve the overall light collection. From an experimentalist’s point of view, simple and fast experimental design tools should be explored. In this work, we investigate the plasmon-related photocurrent enhancements for Si test-solar cells with a number of different metal nanoparticle shapes and materials placed on top of a dielectric layer. The spectral position of the photocurrent-enhancement onset is compared to plasmon resonance calculations based on a fairly simple model. Despite the fact that the optical interactions in nanoparticle solar cell configurations can be quite complex, the photocurrent enhancement in the investigated test-solar cells can be predicted qualitatively well for particles with a plasmon resonance in the visible spectrum. This simple and fast model can be used as a rule of thumb in designing nanoparticle arrays for a specific photocurrent enhancement profile.     

Broadband Tunable and Double Dipole Surface Plasmon Resonance by TiO2 Core/Ag Shell Nanoparticles

A design of a TiO₂ core and Ag shell spherical nanoparticle is theoretically presented. The nanoparticles display double dipole plasmonic resonance peaks: one located at the ultraviolet range, the other is widely tunable from the visible to the near infrared region. The tunability can be easily controlled by varying the sizes of the core and the shell. The near field patterns of the double plasmonic resonance peaks are analyzed, and the dipole resonance modes for those two peaks are confirmed for the suitable core–shell sizes.     

Broad Tunable Nanoantenna Based on Graphene Log-Periodic Toothed Structure

A log-periodic toothed nanoantenna based on graphene is proposed, and its multi-resonance properties with respect to the variations of the chemical potential are investigated. The field enhancement and radar cross-section of the antenna for different chemical potentials are calculated, and the effect of the chemical potential on the resonance frequency is analyzed. In addition, the dependence of the resonance frequency on the substrate is also discussed. It is shown that large modulation of resonance intensity in log-periodic toothed nanoantenna can be achieved via turning the chemical potential of graphene. The tunability of the resonant frequencies of the antenna can be used to broad tuning of spectral features. The property of tunable multi-resonant field enhancement has great prospect in the field of graphene-based broadband nanoantenna, which can be applied in non-linear spectroscopy, optical sensor, and near-field optical microscopy.     

Förster Resonance Energy Transfer Between Molecules in the Vicinity of Graphene-Coated Nanoparticles

The recent demonstration of the plasmonic-enhanced Förster resonance energy transfer (FRET) between two molecules in the vicinity of planar graphene monolayers is further investigated using graphene-coated nanoparticles (GNP). Due to the flexibility of these nanostructures in terms of their geometric (size) and dielectric (e.g., core material) properties, greater tunability of the FRET enhancement can be achieved employing the localized surface plasmons. It is found that while the typical characteristic graphene plasmonic enhancements are manifested from using these GNPs, even higher enhancements can be possible via doping and manipulating the core materials. In addition, the broadband characteristics are further expanded by the closely spaced multipolar plasmon resonances of the GNPs.     

High Optical Transmission in a Hybrid Plasmonic-Optical Structure with a Continuous Metal Film

Metals are naturally opaque for electromagnetic (EM) waves below violet frequency due to the Coulomb screening effect. In this letter, we demonstrate high optical transparency of a seamless continuous metal film by sandwiching it in a hybrid plasmonic-optical structure. The proposed structure consists of a plasmonic array and an optical cavity, which exhibits magnetic plasmon (MP) resonance and optical Fabry-Perot (FP) resonance, respectively. An optical transparency of 84% in the near-IR regime is achieved making use of interaction between the plasmonic and optical modes. Furthermore, spectral tunability of the high transparency is demonstrated and robustness under oblique incidence is examined. This work may give insights into plasmonic-optical interactions and may be a potential candidate for transparent electrodes.     

A Three-Dimensional Plasmonic Nanostructure with Extraordinary Optical Transmission

We report a 3D plasmonic nanostructure having an extraordinary optical transmission due to localized surface plasmon (LSP) coupling between nanoholes and nanodisks. The nanostructure contains a free-standing gold nanohole array (NHA) film above a cavity and an array of nanodisks at the bottom of the cavity that is aligned with the NHA. For the device, the LSP-mediated resonance position was dependent on the hole and nanodisk diameter as well as the separation distance. Also, the effect of LSP coupling between each hole and corresponding nanodisk became negligible for cavities deeper than 200 nm as observed as a disappearance of the LSP resonance. The greatest LSP resonance transmission and the highest electric field intensity were observed for the structure with the shallowest cavity. In addition, the structure had high surface plasmon resonance sensitivity and may have potential for surface-enhanced Raman spectroscopy and optical trapping applications.     

Adaptive Neuro-Fuzzy Appraisal of Plasmonic Studies on Morphology of Deposited Silver Thin Films Having Different Thicknesses

This work presents an experimental analysis on the tunable localized surface plasmon resonance (LSPR), obtained from deposited silver (Ag) thin films of various thicknesses. Silver thin films are prepared using electron beam deposition and undergo an annealing process at different temperatures to produce distinctive sizes of Ag metal nanoparticles (MNPs). The variability of structure sizes and shapes provides an effective means of tuning the position of the LSPR within a wide wavelength range. This paper provides an estimation of LSPR over a broad wavelength range by a process in which the resonance spectra of silver nanoparticles differing in thickness are simulated using an adaptive neuro-fuzzy inference system (ANFIS) method. The ANFIS methodology allows for estimation of sizes of granular structures formed on top of a wafer at certain temperatures, whereupon these intelligent estimators are implemented using MATLAB and their subsequent performances are investigated. The results presented in this paper show the effectiveness of the method of simulation.     

Human and mouse LSP1 genes code for highly conserved phosphoproteins

With use of the mouse LSP1 cDNA we isolated a human homologue of the mouse LSP1 gene from a human CTL cDNA library. The predicted protein sequence of human LSP1 is compared with the predicted mouse LSP1 protein sequence and regions of homology are identified in order to predict structural features of the LSP1 protein that might be important for its function. Both the human and mouse LSP1 proteins consist of two domains, an N-terminal acidic domain and a C-terminal basic domain. The C-terminal domains of the mouse and human LSP1 proteins are highly conserved and include several conserved, putative serine/threonine phosphorylation sites. Immunoprecipitation of LSP1 protein from 32P-orthophosphate-loaded cells show that both the mouse and human LSP1 proteins are phosphoproteins. The sequences of the putative Ca2(+)-binding sites present in the N-terminal domain of the mouse LSP1 protein are not conserved in the human LSP1 protein; however, a different Ca2(+)-binding site may exist in the human protein, indicating a functional conservation rather than a strict sequence conservation of the two proteins. The expression of the human LSP1 gene follows the same pattern as the expression of the mouse LSP1 gene. Southern analysis of human genomic DNA shows multiple LSP1-related fragments of varying intensity in contrast to the simple pattern found after similar analysis of mouse genomic DNA. By using different parts of the human LSP1 cDNA as a probe, we show that most of these multiple bands contain sequences homologous to the conserved C-terminal region of the LSP1 cDNA. This suggests that there are several LSP1-related genes present in the human genome.     

Enhancement of Emission Efficiency of Deep-Ultraviolet AlGaN Quantum Wells Through Surface Plasmon Coupling with an Al Nanograting Structure

The enhancement of the internal quantum efficiency (IQE) of deep-ultraviolet Al _x Ga_1-x N/Al _y Ga_1-y N (x < y) quantum wells (QWs) by fabricating one-dimensional Al nanogratings on a QW structure for inducing surface plasmon (SP) coupling is demonstrated. Through temperature-dependent photoluminescence (PL) measurement, the enhancements of IQE in different emission polarizations are illustrated. Due to the small difference in energy band level between the heavy/light hole and split-off valence bands, the IQEs of the transverse electric- (TE-) and transverse magnetic- (TM-) polarized emissions are about the same. When emission polarization is perpendicular to Al-grating ridges, the SP resonance mode for coupling with the QWs is dominated by localized surface plasmon (LSP). When emission polarization is parallel with Al-grating ridges, the coupled SP resonance mode may mix LSP and SP polariton. In this polarization, LSP can be excited because of the width fluctuation of a grating ridge. When the excitation laser polarization is perpendicular to Al-grating ridges, the strong LSP resonance at the excitation laser wavelength leads to stronger excitation and hence higher IQE levels.