Complementary Aluminum Nanopatch/Nanohole Arrays for Broad Palettes of Colors

Plasmonics - We investigate aluminum nanopatch/nanohole arrays surrounded by a dielectric material on plastic substrates for large area color printing. In this specific arrangement, metallic...     

Extraordinary Optical Transmission Property of X-Shaped Plasmonic Nanohole Arrays

Optical transmission properties of periodic X-shaped plasmonic nanohole arrays in a silver film are investigated by performing the finite element method. Obvious peaks appear in the transmission spectra due to surface plasmon polaritons (SPPs) on the top surface of the silver film, to the Fabry–Ferot resonance effect of SPPs in the nanohole, and to the localized surface plasmon resonance of the nanohole. Besides the topologic shape parameters of the X-shaped nanohole, transmission properties strongly depend on incident polarization. The results of this study not only present a tunable plasmonic filter, but also aid in the understanding of the mechanisms of the extraordinary optical transmission phenomenon.     

Optical Response of Plasmonic Nanohole Arrays: Comparison of Square and Hexagonal Lattices

Nanohole arrays in metal films allow extraordinary optical transmission (EOT); the phenomenon is highly advantageous for biosensing applications. In this article, we theoretically investigate the performance of refractive index sensors, utilizing square and hexagonal arrays of nanoholes, that can monitor the spectral position of EOT signals. We present near- and far-field characteristics of the aperture arrays and investigate the influence of geometrical device parameters in detail. We numerically compare the refractive index sensitivities of the two lattice geometries and show that the hexagonal array supports larger figure-of-merit values due to its sharper EOT response. Furthermore, the presence of a thin dielectric film that covers the gold surface and mimics a biomolecular layer causes larger spectral shifts within the EOT resonance for the hexagonal array. We also investigate the dependence of the transmission responses on hole radius and demonstrate that hexagonal lattice is highly promising for applications demanding strong light transmission.     

Surface-Enhanced Resonance Raman Scattering (SERRS) Using Au Nanohole Arrays on Optical Fiber Tips

Circular and bow tie-shaped Au nanoholes arrays were fabricated on gold films deposited on the tips of single-mode optical fibers. The nanostructures were milled using focused ion beam with a high quality control of their shapes and sizes. The optical fiber devices were used for surface-enhanced resonance Raman scattering (SERRS) measurements in both back- and forward-scattering geometries, yielding promising performance in both detection arrangements. The effect of the hole shape on the SERRS performance was explored with the bow tie nanostructures presenting a better SERRS performance than the circular holes arrays. The results present here are another step towards the development of optical fiber tips modified with plasmonic nanostructures for SERRS applications.

Optical Properties and Local Electromagnetic Field Enhancement of Periodic Rectangular Nanohole Arrays in Au-Interlayer-Au Multilayer Films

Plasmonics - The optical properties and the local electromagnetic field enhancement of a compound structure with rectangular nanohole arrays in Au-interlayer-Au multilayer films are numerically...     

Gold Nanoring Arrays for Near Infrared Plasmonic Biosensing

Gold nanoring array surfaces that exhibit strong localized surface plasmon resonances (LSPR) at near infrared (NIR) wavelengths from 1.1 to 1.6 μm were used as highly sensitive real-time refractive index biosensors. Arrays of gold nanorings with tunable diameter, width, and spacing were created by the nanoscale electrodeposition of gold nanorings onto lithographically patterned nanohole array conductive surfaces over large areas (square centimeters). The bulk refractive index sensitivity of the gold nanoring arrays was determined to be up to 3,780 cm⁻¹/refractive index unit by monitoring shifts in the LSPR peak by FT-NIR transmittance spectroscopy measurements. As a first application, the surface polymerization reaction of dopamine to form polydopamine thin films on the nanoring sensor surface from aqueous solution was monitored with the real-time LSPR peak shift measurements. To demonstrate the utility of the gold nanoring arrays for LSPR biosensing, the hybridization adsorption of DNA-functionalized gold nanoparticles onto complementary DNA-functionalized gold nanoring arrays was monitored. The adsorption of DNA-modified gold nanoparticles onto nanoring arrays modified with mixed DNA monolayers that contained only 0.5 % complementary DNA was also detected; this relative surface coverage corresponds to the detection of DNA by hybridization adsorption from a 50 pM solution.

     

DNA‐Functionalized Plasmonic Nanomaterials for Optical Biosensing

Plasmonic nanomaterials, especially Au and Ag nanomaterials, have shown attractive physicochemical properties, such as easy functionalization and tunable optical bands. The development of this active subfield paves the way to the fascinating biosensing platforms. In recent years, plasmonic nanomaterials–based sensors have been extensively investigated because they are useful for genetic diseases, biological processes, devices, and cell imaging. In this account, a brief introduction of the development of optical biosensors based on DNA‐functionalized plasmonic nanomaterials is presented. Then the common strategies for the application of the optical sensors are summarized, including colorimetry, fluorescence, localized surface plasmon resonance, and surface‐enhanced resonance scattering detection. The focus is on the fundamental aspect of detection methods, and then a few examples of each method are highlighted. Finally, the opportunities and challenges for the plasmonic nanomaterials–based biosensing are discussed with the development of modern technologies.     

Design and Analysis of Infrared Tunable All-Optical Filters Based on Plasmonic Hybrid Nanostructure Using Periodic Nanohole Arrays

A tunable high transmission optical bandpass filter based on a plasmonic hybrid nanostructure, composed of a periodic array of nanocircles and nanoholes combining two isolated waveguides is introduced in this paper. The presented design improves the coupling, which results in a higher transmission peak. To study the filtering operation, different topologies are investigated. The transmission properties and the resonance wavelengths are adjusted by sweeping various geometrical parameters. A multimode spectrum for each of the topologies is obtained. A tunable bandgap and bandwidth can be obtained by adjusting the refractive index of the periodic nanostructure. We have reached a maximum quality factor and a small full width at half-maximum bandwidth with the maximum transmission values greater than 80%. The advantages of the presented structures which include the benefits of both plasmonic and periodic nanostructures are tunability, high detection resolution, and integrability at the nanoscale for optical applications.

     

Optical Absorption in Overcoats of Nanoparticle Arrays on a Metallic Substrate

Surface plasma oscillations in metallic particles as well as in thin metallic films have been studied extensively in the past decades. New features regarding surface plasma excitations are, however, constantly discovered, leading, for example, to surface-enhanced Raman scattering studies and enhanced optical transmission though metal films with nanohole arrays. In the present work, the role of a metallic substrate is examined in two cases, one involving an overcoat of dielectric nanoparticles and the other an overcoat of metallic nanoparticles. Theoretical results are obtained by modeling the nanoparticles as forming a two-dimensional, hexagonal lattice of spheres. The scattered electromagnetic field is then calculated using a variant of the Green function method. Comparison with experimental results is made for nanoparticles of tungsten oxide and tin oxide deposited on either gold or silver substrates, giving qualitative agreement on the extra absorption observed when the dielectric nanoparticles are added to the metallic surfaces. Such absorption would be attributed to the mirror image effects between the particles and the substrate. On the other hand, calculations of the optical properties of silver or gold nanoparticle arrays on a gold or a silver substrate demonstrate very interesting features in the spectral region from 400 to 1,000 nm. Interactions between the nanoparticle arrays surface plasmons and their images in the metallic substrate would be responsible for the red shift observed in the absorption resonance. Moreover, effects of particle size and ambient index of refraction are studied, showing a great potential for applications in biosensing with structures consisting of metallic nanoparticle arrays on metallic substrates.     

A Review on Functionalized Gold Nanoparticles for Biosensing Applications

Nanoparticle technology plays a key role in providing opportunities and possibilities for the development of new generation of sensing tools. The targeted sensing of selective biomolecules using functionalized gold nanoparticles (Au NPs) has become a major research thrust in the last decade. Au NP-based sensors are expected to change the very foundations of sensing and detecting biomolecules. In this review, we will discuss the use of surface functionalized Au NPs for smart sensor fabrication leading to detection of specific biomolecules and heavy metal ions.     

Effects of Refractive Index Variations on the Optical Transmittance Spectral Properties of the Nano-Hole Arrays

The 3D finite difference time domain technique was carried out to study the optical transmission properties of nano-hole arrays in the gold thin film supported by materials with different index of refraction in the visible and infrared regions. A series of perforated nano-hole structures on the gold film at different hole radius, hole depth of 100 nm, and structural periodicity of 400 nm were studied. It was found that transmission properties (i.e., intensity, FWHM, and resonance position) were strongly affected by hole radius and surrounding medium index of refraction. The maximum optical transmittance was observed as 31.9 % in a nano-hole array of hole radius of 125 nm and refractive index of 1.3. The maximum sensitivity of 300 nm/RIU was obtained at index of refraction of 1.7, whereas the minimum one was calculated as 110 nm/RIU in a nano-hole array of hole radius of 50 nm. It was also found that on increasing the hole radius from 50 to 125 nm, the spectral sensitivity was decreased, whereas the index sensitivity was increased on increasing the refractive index.     

A Systematic Study on Au-Capped Si Nanowhiskers for Size-Dependent Improved Biosensing Applications

Plasmonics - Reducing the distance between the fluorescence molecules and noble metal (resonant) nanostructures is known to advance the process of electromagnetic coupling and energy transfer,...     

Properties of Thermally Dewetted Thin Au Films on ITO-Coated Glass for Biosensing Applications

Plasmonics - Noble metal nanostructures are object of great interest due to their unique optical and electronic properties exploited in nanotechnology, medicine, biochemistry, and surface-enhanced...     

Effect of Boundary Condition and Periodical Extension on Transmission Characteristics of Terahertz Filters with Periodical Hole Array Structure Fabricated on Aluminum Slab

Terahertz (THz) filters based on extraordinary optical transmission from periodical hole array structures fabricated on aluminum slab have been experimentally investigated by using THz time-domain spectroscopy. The incident THz pulses with frequency from 0.1 to 2.7 THz could be partly filtered, and the central peak was at ～0.26. The high frequency signal could be observed to decrease, especially for the frequency above ～1 THz. Moreover, the transmission peak from small-size sample with less hole arrays shifts to high frequency at ～0.53 THz due to both the effects of boundary condition and insufficient periodical extension. Furthermore, finite element method with surface plasmon polariton theory is employed to analyze this extraordinary optical transmission and filter phenomena.     

Hybrid Dielectric-Loaded Plasmonic Waveguide-Based Power Splitter and Ring Resonator: Compact Size and High Optical Performance for Nanophotonic Circuits

The key challenge of the plasmonic waveguide is to achieve simultaneously both the long propagation length and high confinement. The hybrid dielectric-loaded plasmonic waveguide consists of a SiO₂ stripe sandwiched between a Si-nanowire and a silver film and thus promises as a best candidate to overcome this challenge. We propose to exploit this unique property of this structure to design different high-efficient silicon-based plasmonic components including waveguide, power splitter, and wavelength-selective ring resonator. As a result, the proposed power splitter with a waveguide cross section (λ ²/60) and a strong mode confinement area (~λ ²/240) features a low power transmission loss (<0.4 dB) at the optimal arm length of 4 μm with respect to different separation distances of output arms. Moreover, we also demonstrate that a plasmonic ring resonator with a compact ring radius of 2 μm may achieve high optical performance such as high-extinction ratio of 30 dB, large free spectral range of 67 nm, and small bandwidth of 0.6 nm. These superior performances make them promising building blocks for integrated nanophotonic circuits.     

Design of Aluminum Bowtie Nanoantenna Array with Geometrical Control to Tune LSPR from UV to Near-IR for Optical Sensing

Plasmonics - Plasmonic nanoantennas have earned strong recognition for their unique capability to confine light from free space into sub-wavelength dimensions with strong electric field (E-field)...     

Mechanisms Responsible for Extraordinary Optical Transmission Through One-Dimensional Periodic Arrays of Infinite Sub-wavelength Slits: the Origin of Previous EOT Position Prediction Misinterpretations

We have studied theoretically and numerically the effect of extraordinary optical transmission of light propagating through the one-dimensional periodic arrays of infinite slits with sub-wavelength dimensions. In our study, we have concentrated on mechanisms which are responsible for this effect. Within our analysis, we have attempted to draw the attention towards the origin and reasons of earlier misinterpretations concerning the spectral position of EOT prediction and the related role of surface plasmon polaritons in manifestation of the effect. Using the sequence of suitable parameter two-dimensional spaces (in terms of structure period-filling factor; thickness-wavelength; wavelength-angle), we were able to look into subtle physical mechanisms operating in the background of this extraordinary optical transmission effect. To study these effects associated with the extraordinary optical transmission, we have applied our efficient two-dimensional numerical technique based on the rigorous coupled-wave analysis. Within the thickness-wavelength parameter space, we have been able to identify and describe three distinct interaction regions, with specific behaviour. Finally, we have proposed and discussed the supporting mechanism explaining the interaction, based on the interference of resonant and non-resonant contributions at the slit openings.     

Radioimmunoassay on Polycarbonate Membranes: a Sensitive and Simplified Method for the Detection and Quantitation of Antibody

A new radioimmunoassay technique is described in which a sampling manifold and polycarbonate filter membranes are used. Antigen-antibody reactions take place on the membranes. The manifold permits the simultaneous running of 30 samples and a rapid wash technique in which the washing solution is introduced into the manifold wells and suctioned off from below. The polycarbonate membrane offers a distinct advantage over the cellulose acetate in that nonspecific protein adsorption is substantially reduced. Antigens employed are whole bacteria or soluble antigen coupled to Sepharose beads and are layered over the membrane surface. A radiolabeled antibody is used to measure the primary antigen-antibody interaction. The sensitivity of the procedure is equal to that of fluorescent antibody tests.     

Refined Model for Plasmon Ruler Based on Catenary-Shaped Optical Fields

Plasmonics - The catenary, in addition to be one intriguing structure in mechanics and optics, expresses the universal rule of evanescent field coupling between metallic or dielectric nanoparticle...