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.     

Elucidating the Signal Responses of Multi-Parametric Surface Plasmon Resonance Living Cell Sensing: A Comparison between Optical Modeling and Drug–MDCKII Cell Interaction Measurements

In vitro cell-based assays are widely used during the drug discovery and development process to test the biological activity of new drugs. Most of the commonly used cell-based assays, however, lack the ability to measure in real-time or under dynamic conditions (e.g. constant flow). In this study a multi-parameter surface plasmon resonance approach in combination with living cell sensing has been utilized for monitoring drug-cell interactions in real-time, under constant flow and without labels. The multi-parameter surface plasmon resonance approach, i.e. surface plasmon resonance angle versus intensity plots, provided fully specific signal patterns for various cell behaviors when stimulating cells with drugs that use para- and transcellular absorption routes. Simulated full surface plasmon resonance angular spectra of cell monolayers were compared with actual surface plasmon resonance measurements performed with MDCKII cell monolayers in order to better understand the origin of the surface plasmon resonance signal responses during drug stimulation of cells. The comparison of the simulated and measured surface plasmon resonance responses allowed to better understand and provide plausible explanations for the type of cellular changes, e.g. morphological or mass redistribution in cells, that were induced in the MDCKII cell monolayers during drug stimulation, and consequently to differentiate between the type and modes of drug actions. The multi-parameter surface plasmon resonance approach presented in this study lays the foundation for developing new types of cell-based tools for life science research, which should contribute to an improved mechanistic understanding of the type and contribution of different drug transport routes on drug absorption.     

Modulation of Optical Properties of Gold Nanorods on Addition of KOH

Gold nanorods are known to exhibit two distinct surface plasmon oscillations namely, transverse and longitudinal bands corresponding to oscillations of conduction electrons along width and length of gold nanorods. Considerable changes in these surface plasmon resonance peak positions occurred when KOH was added to the nanorod solution. Nanorods with initial longitudinal plasmon band at 739, 796, and 895 nm are studied with variation in KOH concentration. While the longitudinal plasmon resonance peak showed blue shift, transverse plasmon resonance peak exhibited only intensity variations. Changes could be attributed to the shape transition of gold nanorods on variation of pH in the solution. Shape transition of gold nanorods is confirmed by transmission electron microscopy images.     

Sensitivity Enhanced by MoS2–Graphene Hybrid Structure in Guided-Wave Surface Plasmon Resonance Biosensor

Plasmonics - Compared with surface plasmon resonance (SPR) biosensor, guided-wave surface plasmon resonance (GWSPR) biosensor has a higher sensitivity. In order to further enhance the sensitivity...     

Surface Plasmon as a Probe of Local Field Enhancement

New method of experimental determination of local field enhancement at metal nanoparticles is suggested. It uses surface plasmon as a probe. Alternating-sign shift of surface plasmon resonance in copper nanoparticles incorporated in silica matrix has been observed under irradiation by intense femtosecond laser pulse. The red shift of plasmon observed during the action of pump pulse is interpreted as a result of change of dielectric constant of silica matrix due to optical Kerr effect in electric field of pump pulse enhanced in a vicinity of metal nanoparticles. The field enhancement factor is estimated from the value of the observed red shift of plasmon resonance.     

Size and Temperature Effects on the Surface Plasmon Resonance in Silver Nanoparticles

The surface plasmon energy in spherical silver nanoparticles embedded in silica host matrix depends on the size and temperature of the nanoparticles. The dependences of the surface plasmon energy were studied for silver nanoparticles in the size range 11?C30?nm and in the temperature interval 293?C650?K. As the size of the nanoparticles decreases or the temperature increases, the surface plasmon resonance shifts to red. When the size of the nanoparticles decreases, the scattering rate of the conduction electrons increases, which results in the nonlinear red shift of the surface plasmon resonance. The red shift with temperature is linear for larger nanoparticles and becomes nonlinear for smaller ones. As the temperature of the nanoparticles increases, the volume thermal expansion of the nanoparticles leads to the red shift of the surface plasmon resonance. The thermal volume expansion coefficient depends on the size and temperature. It increases with a decrease of the nanoparticle size and an increase of the temperature.     

Plasmon Hybridization in Silver Nanoislands as Semishells Arrays Coupled to a Thin Metallic Film

We obtained experimentally strong plasmon interactions between localized surface plasmon with delocalized surface plasmon polaritons in a new nanosystem of silver semishells island film arrays arranged as a closed-packing structure coupled to an adjacent thin silver film. We show that plasmon interactions for such a nanosystem exhibits two pronounced resonances and interpret the coupling in terms of Fano resonances. The higher energy resonance is identified as a symmetric hybridization mode between localized plasmon resonances in the island semishell array and surface plasmon polaritons in the metal film and while the lower energy resonance is identified as a corresponding anti-symmetric hybridization mode. Increasing the size of the particle arrays enhances and red shifts the resonances. We show that adding a dielectric spacer between the semishell island array and the metal film results in a red shifting of the resonances and introduce an additional high energy spectral peak. The effect of the spacer layer is interpreted as a reduced hybridization and the generation of additional localized surface plasmon resonances.     

Lifetime of Enhanced Graphene Surface Plasmon and Superstrate Sensitivity

Plasmonics - We investigated the field enhancement and lifetime of tuning surface plasmon in zero-thickness nanostructured graphene patches. The graphene surface plasmon (GSP) resonance mechanism...     

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...     

Manipulation of Plasmon Dephasing Time in Nanostructure Arrays Via the Far-Field Coupling

Plasmonics - On-demand manipulation of the plasmon dephasing time plays critical roles in many important applications of localized surface plasmon resonance. Here, we systemically investigate the...     

Numerical Simulation of Extinction Spectra of Plasmonically Coupled Nanospheres Using Discrete Dipole Approximation: Influence of Compositional Asymmetry

We demonstrate plasmon coupling phenomenon between equivalent (homodimer) and non-equivalent (heterodimer) spherical shape noble metal nanoparticle (Ag, Au and Al). A systematic comparison of surface plasmon resonance (SPR) and extinction properties of various configurations (monomer, homodimer and heterodimer) has been investigated to observe the effect of compositional asymmetry. Numerical simulation has been done by using discrete dipole approximation method to study the optical properties of plasmonically coupled metal nanoparticles (MNPs). Plasmon coupling between similar nanoparticles allows only higher wavelength bonding plasmon mode while both the plasmon modes lower wavelength antibonding mode as well as higher wavelength bonding mode in the case of heterodimer. Au monomer of radius 50 nm shows resonance peak at 518 nm while plasmon coupling between Au-Au homodimer results in a spectral red shift around 609 nm. Au-Ag plasmonic heterodimer (radius 50 nm) reveals two resonant modes corresponding to higher energy antibonding mode (422 nm) as well as lower energy bonding mode (533 nm). Further, we have shown that interparticle edge-to-edge separation is the most significant parameter affecting the surface plasmon resonances of MNPs. As the inter particle separation decreases, resonance wavelength shows red spectral shift which is maximum for the touching condition. It is shown that plasmon coupling is a reliable strategy to tune the SPR.

     

Localized Surface Plasmon Resonance and Refractive Index Sensitivity of Metal–Dielectric–Metal Multilayered Nanostructures

The localized surface plasmon resonances of multilayered nanostructures are studied using finite difference time domain simulations and plasmon hybridization method. Concentric metal–dielectric–metal (MDM) structure with metal core and nanoshell separated by a thin dielectric layer exhibits a strong coupling between the core and nanoshell plasmon resonance modes. The coupled resonance mode wavelengths show dependence on the dielectric layer thickness and composition of core and outer layer metal. The aluminum-based MDM structures show lower plasmon wavelength compared with Ag- and Au-based MDM nanostructures. The calculated refractive index sensitivity (RIS) factor is in the order Ag–Air–Ag>Au–Air–Au>Al–Air–Al for monometallic multilayered nanostructures. Bimetallic multilayered nanostructures support strong and tunable plasmon resonance wavelengths as well as high RIS factor of 510 nm/refractive index unit (RIU) and 470 nm/RIU for Al–Air–Au and Ag-Air-Au, respectively. The MDM structures not only exhibit higher index sensitivity but also cover a wide ultraviolet–near-infrared wavelengths, making these structures very promising for index sensing, biomolecule sensing, and surface-enhanced Raman spectroscopy.     

The Optimal Aspect Ratio of Gold Nanorods for Plasmonic Bio-sensing

The plasmon resonance of metal nanoparticles shifts upon refractive index changes of the surrounding medium through the binding of analytes. The use of this principle allows one to build ultra-small plasmon sensors that can detect analytes (e.g., biomolecules) in volumes down to attoliters. We use simulations based on the boundary element method to determine the sensitivity of gold nanorods of various aspect ratios for plasmonic sensors and find values between 3 and 4 to be optimal. Experiments on single particles confirm these theoretical results. We are able to explain the optimum by showing a corresponding maximum for the quality factor of the plasmon resonance.     

Quantized plasmon quenching dips nanospectroscopy via plasmon resonance energy transfer

We observed quantized plasmon quenching dips in resonant Rayleigh scattering spectra by plasmon resonance energy transfer (PRET) from a single nanoplasmonic particle to adsorbed biomolecules. This label-free biomolecular absorption nanospectroscopic method has ultrahigh molecular sensitivity.     

Metal-Dielectric-Graphene Hybrid Heterostructures with Enhanced Surface Plasmon Resonance Sensitivity Based on Amplitude and Phase Measurements

Metal-dielectric-graphene hybrid heterostructures based on oxides Al₂O₃, HfO₂, and ZrO₂ as well as on complementary metal–oxide–semiconductor compatible dielectric Si₃N₄ covering plasmonic metals Cu and Ag have been fabricated and studied. We show that the characteristics of these heterostructures are important for surface plasmon resonance biosensing (such as minimum reflectivity, sharp phase changes, resonance full width at half minimum and resonance sensitivity to refractive index unit (RIU) changes) can be significantly improved by adding dielectric/graphene layers. We demonstrate maximum plasmon resonance spectral sensitivity of more than 30,000 nm/RIU for Cu/Al₂O₃ (ZrO₂, Si₃N₄), Ag/Si₃N₄ bilayers and Cu/dielectric/graphene three-layers for near-infrared wavelengths. The sensitivities of the fabricated heterostructures were?~?5–8 times higher than those of bare Cu or Ag thin films. We also found that the width of the plasmon resonance reflectivity curves can be reduced by adding dielectric/graphene layers. An unexpected blueshift of the plasmon resonance spectral position was observed after covering noble metals with high-index dielectric/graphene heterostructures. We suggest that the observed blueshift and a large enhancement of surface plasmon resonance sensitivity in metal-dielectric-graphene hybrid heterostructures are produced by stationary surface dipoles which generate a strong electric field concentrated at the very thin top dielectric/graphene layer.

     

Characterization of a Wnt-binding site of the WIF-domain of Wnt inhibitory factor-1

A Wnt-binding site of the WIF-domain of Wnt inhibitory factor-1 was localized by structure-guided arginine-scanning mutagenesis in combination with surface plasmon resonance assays. Our observation that substitution of some residues of WIF resulted in an increased affinity for Wnt5a, but decreased affinity for Wnt3a, suggests that these residues may define the specificity spectrum of WIF for Wnts. These results hold promise for a more specific targeting of Wnt family members with WIF variants in various forms of cancer.

Structured summary of protein interactions

WIFbinds to Wnt7a by surface plasmon resonance (View Interaction)WIFbinds to Wnt4 by surface plasmon resonance (View Interaction)WIF and Wnt3aphysically interact by competition binding (View Interaction 1, 2, 3, 4,5, 6)WIFbinds to Wnt9b by surface plasmon resonance (View Interaction)WIFbinds to Wnt5a by surface plasmon resonance (View Interaction)WIFbinds to Wnt11 by surface plasmon resonance (View Interaction)WIFbinds to Wnt3a by surface plasmon resonance (View Interaction)Wnt-5a and WIFphysically interact by competition binding (View Interaction 1,2, 3, 4, 5, 6)     

Compact Color Filter and Polarizer of Bilayer Metallic Nanowire Grating Based on Surface Plasmon Resonances

Surface plasmon resonances on bilayer aluminum nanowire gratings are studied in both theory and experiment. It is found that there are two kinds of surface plasmon on the bilayer metallic gating: longitudinal aluminum/dielectric/aluminum slit and lateral aluminum/dielectric interface waveguide mode. The surface plasmon waveguide mode resonance in the slits makes the grating act as a transverse magnetic (TM)-passing polarizer. With the lateral waveguide mode resonance, certain wavelengths of the incident TM light are translated to aluminum/air or aluminum/substrate waveguide light, and the grating acts as a color filter. With both resonances, the bilayer nanowire grating can be a compact-integrated polarizer and color filter.     

Systematic Study of the Surface Plasmon Resonance Signals Generated by Cells for Sensors with Different Characteristic Lengths

The objectives of this study were to establish an in-depth understanding of the signals induced by mammalian cells in surface plasmon resonance (SPR) sensing. To this end, two plasmonic structures with different propagation and penetration distances were used: conventional surface plasmon resonance and long-range surface plasmon resonance. Long-range SPR showed a lesser sensitivity to the absolute number of round cells but a greater resolution due to its very narrow spectral dip. The effect of cell spreading was also investigated and the resonance angle of long-range SPR was mostly insensitive unlike in the conventional SPR counterpart. Experimental data was compared with suitable models used in the SPR literature. Although these simple averaging models could be used to describe some of the experimental data, important deviations were observed which could be related to the fact that they do not take into consideration critical parameters such as plasmon scattering losses, which is particularly crucial in the case of long-range SPR structures. The comparison between conventional and long-range SPR for cellular schemes revealed important fundamental differences in their responses to the presence of cells, opening new horizons for SPR-based cell assays. From this study, long-range SPR is expected to be more sensitive towards both the detection of intracellular events resulting from biological stimulation and the detection of microorganisms captured from complex biological samples.     

Double Directions Nanoscale Range Finding Using Fano Resonance in Coupled Gratings

In this paper, a theoretical demonstration is given of nanoscale range finding by exciting Fano resonance in coupled gratings. Metallic ridges induce oscillation mode, whose interference with surface plasmon polartions generate narrow Fano resonance. The concept of hybridization is employed to understand the coupling effect of surface plasmon polartions and the oscillation due to metallic ridges. Fano behavior in this structure is captured by using the temporal coupled-mode theory. The gained fundamental understanding opens up new ways to control nanoscale spacing distances and tailor Fano resonance, thus facilitating rational design of nanosensors to improve the performance of nanomotion control systems.

     

Coupled plasmon-waveguide resonators: a new spectroscopic tool for probing proteolipid film structure and properties.

A variant of surface plasmon resonance (SPR) spectroscopy has been developed that involves a coupling of plasmon resonances in a thin metal film and waveguide modes in a dielectric overcoating. This new technique is referred to as coupled plasmon-waveguide resonance (CPWR) spectroscopy. It combines a greatly enhanced sensitivity (due to increased electromagnetic field intensities at the dielectric surface) and spectral resolution (due to decreased resonance linewidths), with the ability to directly measure anisotropies in refractive index and optical absorption coefficient in a dielectric film adsorbed onto the surface of the overcoating. Experimental data obtained with an egg phosphatidylcholine bilayer are presented to document these properties.