A surface plasmon resonance probe with a novel integrated reference sensor surface

A surface plasmon resonance (SPR) sensor probe with integrated reference surface is described. In order to fabricate the integrated reference surface, two dielectric layers with different thickness were deposited on the single gold SPR sensor surface via plasma polymerization of hexamethyldisiloxane. The working sensor surface was a 34 nm dielectric layer with immobilized bovine serum albumin (BSA) antigen and an adjacent thin 1 nm dielectric layer without BSA provided reference surface. A specific immunoreaction of anti-BSA antibody was detected after immersion of the SPR probe into sample solution. Simultaneous observation of reference and working surface response enabled determination of the immunoreaction without the need for the baseline measurement. Moreover, compensation of nonspecific adsorption could be confirmed using anti-human serum albumin antibody.     

Improvement of Transparent Metal Top Electrodes for Organic Solar Cells by Introducing a High Surface Energy Seed Layer

We present highly transparent and conductive silver thin films in a thermally evaporated dielectric/metal/dielectric (DMD) multilayer architecture as top electrode for efficient small molecule organic solar cells. DMD electrodes are frequently used for optoelectronic devices and exhibit excellent optical and electrical properties. Here, we show that ultrathin seed layers such as calcium, aluminum, and gold of only 1 nm thickness strongly influence the morphology of the subsequently deposited silver layer used as electrode. The wetting of silver on the substrate is significantly improved with increasing surface energy of the seed material resulting in enhanced optical and electrical properties. Typically thermally evaporated silver on a dielectric material forms rough and granular layers which are not closed and not conductive below thicknesses of 10 nm. With gold acting as seed layer, the silver electrode forms a continuous, smooth, conductive layer down to a silver thickness of 3 nm. At 7 nm silver thickness such an electrode exhibits a sheet resistance of 19 Ω/□ and a peak transmittance of 83% at 580 nm wavelength, both superior compared to silver electrodes without seed layer and even to indium tin oxide (ITO). Top‐illuminated solar cells using gold/silver double layer electrodes achieve power conversion efficiencies of 4.7%, which is equal to 4.6% observed in bottom‐illuminated reference devices employing conventional ITO. The top electrodes investigated here exhibit promising properties for semitransparent solar cells or devices fabricated on opaque substrates.     

Tuning the Dipolar Plasmon Hybridization of Multishell Metal-Dielectric Nanostructure: Gold Nanosphere in a Gold Nanoshell

Because of the interaction between dipole resonances of the inner gold sphere and the outer gold shell, gold-dielectric-gold multishells with sub-50 nm diameter may at most have three hybridization modes of surface plasmon resonance (SPR). Theoretical calculations based on quasi-static theory indicate that there are blending and splitting of SPR bands in the absorption spectra, which makes the number of absorption peak tunable by changing the radius of inserted gold sphere, thickness of gold shell, dielectric constant of middle dielectric shell or outer environment. The two absorption peaks at longer wavelength, which correspond to the hybridization from the bonding shell plasmon and the sphere plasmon, are usually intense and well tunable. The absorption peak at shorter wavelength, which corresponds to the symmetric coupling between the anti-bonding shell plasmon and the sphere plasmon, is relative weak and only occurs with large dielectric constant of the middle shell, small dielectric constant of the outer surrounding, large inner radius of the gold shell, and small radius of the inner gold sphere. Furthermore, the physical origin of these plasmon hybridizations in gold-dielectric-gold multishells nanostructure has also been illuminated by analyzing the local electric field distributions.     

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.     

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.     

Search of Extremely Sensitive Near-Infrared Plasmonic Interfaces: A Theoretical Study

The sensitivity of the wavelength position of localized surface plasmon resonance (LSPR) in metal nanostructures to local changes in the refractive index has been widely used for label-free detection strategies. Tuning the optical properties of the nanostructures from the visible to the infrared region is expected to have a drastic effect on the refractive index sensitivity. Here, we theoretically investigate the optical response of a newly designed plasmonic interface to changes in the bulk refractive index by the finite difference time domain method. It consists of a structured interface, where the planar interface is superposed with dielectric pillars 30 nm in height and 125 nm in length with a separation distance of 15 nm. The pillars are covered with U-shaped gold nanostructures of 50 nm in height, 125 nm in length, and 5 nm of gold base thickness. The whole structure is finally covered with a 5-nm thick dielectric layer of n ₂?=?2.63. This plasmonic structure shows bulk refractive index sensitivities up to 1750 nm/RIU (RIU : refractive index unit) in the near infrared (λ?=?2621 nm). The enhanced sensitivity is a consequence of the extremely enhanced electrical field between the gold nanopillars of the plasmonic interface.     

Multichannel quartz crystal microbalance array: Fabrication,evaluation, application in biomarker detection

A multichannel quartz crystal microbalance array (MQCM) with three pairs of gold electrodes was fabricated for detection of two biomarkers: acetone and nitric oxide (NO). The gold electrodes were deposited symmetrically on an AT-cut 10 MHz circular quartz plate using photolithography, sputtering, and lift-off technologies. The effect of gold layer thickness on MQCM performance was investigated and the optimized thickness was 101 nm. The simulation values of the electric parameters C₀, C_q, L_q, and R_q in the Butterworth–Van Dike equivalent circuit for the MQCM device were 97 pF, 1.3 pF, 1.05 mH, and 9.8 Ω, respectively. Simulation values were in the theoretical range, which indicated that the fabricated MQCM device had good resonance performance. Two types of nanocomposites, titanium dioxide–multiwalled carbon nanotubes and cobalt (II)phthalocyanine–silica, were synthesized as sensing materials. The sensing mechanism is based on coordination adsorption of target molecules onto the sensing material, resulting in a resonant frequency shift of modified QCM sensor. A linear range from 4.33 to 129.75 ppmv for acetone was obtained and one from 5.75 to 103.45 ppbv for NO.     

Construction of simultaneous SPR and QCM sensing platform

To construct a novel simultaneous SPR and QCM sensing system, an AT-cut quartz crystal is fabricated by sputtering 250 nm of ITO on one side of the quartz plate over a 5-nm thick underlay of titanium, while a 50-nm thick layer of gold is sputter-deposited on the other side to induce a total light reflection of an incident laser beam on the thin gold layer. The signals of the sensing system are detected using a Handy-SPR and QCA922 when dropping 200 μL of Milli-Q water into the sensing cell. A decrease in the SPR reflected light intensity is clearly identified. In the same experiment, the changes in the resonant frequency and resistance are about 2 kHz and 200 Ω, respectively. Furthermore, the oscillation stabilities of the resonant frequency and resistance are about 50 Hz and 2 Ω, respectively, which are sufficient to detect a large mass change on the QCM/SPR chip.     

Plasmonic Properties of Silver Nanoparticles on Two Substrates

In this paper, we examine the plasmonic properties of silver nanoparticles, with an emphasis on the sensitivity of the extinction spectra on the supporting substrate: silica (SiO₂) microsphere and indium tin oxide (ITO) coated glass slide, on which silver particles are deposited electroless and electrochemically, respectively. The microstructures and phases of these nanoparticles are characterized by transmission electron microscopy, field emission electron microscopy and X-ray diffraction analysis. The surface plasmon resonance (SPR) properties which are experimentally measured in the ultraviolet-visible-near infrared spectral region are compared to electrodynamics calculations based on the discrete dipole approximation. A wide SPR band ranging from 400 to 800 nm is observed for the silver nanoparticles on a silica microsphere, which is similar to the plasmon resonance characteristics of metal nanoshells. The SPR of a conducting substrate, however, has an effect on the plasmonic properties of silver nanoparticles at longer wavelength.      

Spectral Tuning of Plasmon Resonances of Bimetallic Noble Metal Alloy Nanoparticles Through Compositional Changes

The optical absorption properties of the bimetallic noble metal alloy (viz. Au-Ag, Au-Cu, and Ag-Cu) nanoparticles (NPs) of radii of 10 nm and 20 nm embedded in silica glass have been studied theoretically using a simple model based on the effective medium theory. Our study reveals that the spectra of the above bimetallic alloy NPs exhibit single but composition-sensitive surface plasmon resonance (SPR) peak which indicates the successful formation of alloys. The position of the SPR peak that appeared corresponding to alloy NPs is different from that of the component metals. The study further reveals that the Ag-Au and Au-Cu alloy systems are completely miscible over the entire concentration range but Ag-Cu is miscible up to a certain extent, although, their SPR peak shows a linear shift with molar concentration. It has been further observed that the phase of the Ag-Au alloy system changes with concentration of Au during the alloy formation but no such change is seen in the other two systems. Thus, our study shows that the Ag-Cu system which otherwise does not form alloy in bulk may form alloy in nanoscale with limited miscibility. A shift of the SPR peak positions from ~ 405 to ~ 535 nm for Au-Ag, from ~ 535 to ~ 590 nm for Au-Cu, and from ~ 405 to ~ 436 nm for Ag-Cu NP systems has been observed for different composition of constituent monometals. The compositional changes lead to a spectral tuning of the SPR of the system under studies.

     

Comparative Theoretical Study of the Optical Properties of Silicon/Gold,Silica/Gold Core/Shell and Gold Spherical Nanoparticles

The scattering and absorption efficiencies of light by individual silicon/gold core/shell spherical nanoparticles in air are analysed theoretically in the framework of Lorenz-Mie formalism. We have addressed the influence of particle-diameter and gold-shell thickness on the scattering and absorption efficiencies of such nano-heterostructures. For comparison, we also considered the famous silica/gold core/shell nanoparticle and pure gold nanoparticle. Our simulation clearly shows that the optical response of the illuminated Si/Au core/shell nanoparticle differs markedly from that of the famous SiO₂/Au heterostructure which in turn does not show a significant difference with that of the pure gold nanoparticle. This difference is clearly evident for shell thickness to outer particle radius ratio of less than 0.5. It manifests itself essentially by the occurrence of a strong and sharp absorption resonance beyond the wavelength of 600 nm where the silica/gold and the pure gold nanoparticles never absorb. The characteristics of this resonance are found to be sensitive to the particle diameter and the shell thickness. In particular, its spectral position can be adjusted over a wide spectral range from the visible to the mid-IR by varying the particle diameter and/or the shell thickness.     

Enhanced Optical Absorption and Spectral Photocurrent in a-Si:H by Single- and Double-Layer Silver Plasmonic Interfaces

Single and double plasmonic interfaces consisting of silver nanoparticles embedded in media with different dielectric constants including SiO₂, SiN_x, and Al:ZnO have been fabricated by a self-assembled dewetting technique and integrated to amorphous silicon films. Single plasmonic interfaces exhibit plasmonic resonances whose frequency is red-shifted with increasing particle size and with the thickness of a dielectric spacer layer. Double plasmonic interfaces consisting of two different particle sizes exhibit resonances consisting of double minima in the transmittance spectra. The optical extinction of a-Si:H deposited on these interfaces is broadened into the red indicating higher absorption and/or scattering at wavelengths higher than those typically absorbed by a-Si:H without plasmonic interfaces. While the photocurrent shows an overall decrease for the samples with the interfaces, significant enhancement of photocurrent is observed near the low-energy edge of the bandgap (600–700 nm). These results correlate well with the broadened extinction spectra of the interfaces and are interpreted in terms of enhanced absorption in that region.     

In-Plane and Out-of-Plane Plasmons in Random Silver Nanoisland Films

Effective permittivity of closely spaced random nanoparticles supported by a substrate has been calculated using a modified Yamaguchi’s model (MYM) which involves the exact expression of a local field outside a metal nanoparticle (NP) along with the effective-medium approach. Pulsed laser deposition has been used to deposit silver nanoisland films on SiO₂ substrates. In-plane and out-of-plane plasmonic responses have been calculated using MYM for various filling fractions and the results are compared with those obtained from spectroscopic ellipsometry. Distinct features of out-of-plane and in-plane plasmons are observed with an spectroscopic ellipsometer and their behavior is supported by the present theoretical investigation. The comparison of the effective dielectric constants of the films obtained from ellipsometry data with those calculated using MYM shows uniaxial optical anisotropy in our case. The calculated morphological parameters (filling fraction, aspect ratio, and average particle size) using MYM are also found to be consistent with those obtained from FESEM images.     

A Study of the Surface Plasmon Resonance of Silver Nanoparticles by the Discrete Dipole Approximation Method: Effect of Shape,Size, Structure,and Assembly

The surface plasmon resonance (SPR) of silver nanoparticles (AgNPs) was studied with the discrete dipole approximation considering different shapes, sizes, dielectric environments, and supraparticles assemblies. In particular, we focused our simulations on AgNPs with sizes below 10 nm, where the correction of silver dielectric constant for intrinsic size effects is necessary. We found that AgNPs shape and assembly can induce distinctive features in the extinction spectra and that SPR is more intense when AgNPs have discoid or flat shapes and are embedded in a dielectric shell with high refractive index. However, the SPR loses much of its distinctive features when size effects and stabilizing molecules induce significant broadening of the extinction bands that is often observed in the case of thiolated AgNPs smaller than about 5 nm. These results are useful indications for in situ characterization and monitoring of AgNPs synthesis and for the engineering of AgNPs with new plasmonic properties.     

Design and Research of Enhanced LED Performance Based on Graphical Substrate with Multilayer Hyperbolic Metamaterials

This paper mainly studies the influence of multilayer hyperbolic metamaterials (HMMs) with different structural parameters on the intensity of spontaneous radiation of quantum wells, thereby improving the coupling efficiency of incident electromagnetic waves and free electrons on metal nano-surfaces. In this paper, numerical simulations of visible light bands of 450–700 nm of Ag, Au, and Cu thin films are performed. The local field enhancements of multilayer HMMs with different shapes are compared, and it is found that circle Ag/Si multilayer HMMs have stronger field enhancement effects than other structures. At the same time, Purcell analysis was performed by changing various parameters of multilayer HMMs. It is found that the thickness of the metal/dielectric layer, the distance between the dipole and the HMMs, and the length of the multilayer HMMs change the intensity of the plasmon resonance radiation and have a great impact on the position of the resonance wavelength.

     

The study of genomic DNA adsorption and subsequent interactions using total internal reflection ellipsometry

The adsorption of genomic DNA and subsequent interactions between adsorbed and solvated DNA was studied using a novel sensitive optical method of total internal reflection ellipsometry (TIRE), which combines spectroscopic ellipsometry with surface plasmon resonance (SPR). Single strands of DNA of two species of fish (herring and salmon) were electrostatically adsorbed on top of polyethylenimine films deposited upon gold coated glass slides. The ellipsometric spectra were recorded and data fitting utilized to extract optical parameters (thickness and refractive index) of adsorbed DNA layers. The further adsorption of single stranded DNA from an identical source, i.e. herring ss-DNA on herring ss-DNA or salmon ss-DNA on salmon ss-DNA, on the surface was observed to give rise to substantial film thickness increases at the surface of about 20-21 nm. Conversely adsorption of DNA from alternate species, i.e. salmon ss-DNA on herring ss-DNA or herring ss-DNA on salmon ss-DNA, yielded much smaller changes in thickness of 3-5 nm. AFM studies of the surface roughness of adsorbed layers were in line with the TIRE data.     

Optimizing the Tin Selenide (SnSe) Allotrope/Gold-Based Surface Plasmon Resonance Sensors for Enhanced Sensitivity

The 2D material tin selenide monolayer (SnSe) has attracted a lot of attention due to its excellent optoelectronic properties. This study focuses on the investigation of the potential improvement of the response of surface plasmon resonance (SPR) sensors by coating the gold layer with SnSe allotrope (α, δ, ε) monolayers. Using an optimization algorithm along with the transfer matrix method (TMM), we determined the optimal thickness of the gold layer as a function of the number of monolayers added to significantly increase the sensor’s response in terms of reflectivity and phase. With respect to reflectivity, sensitivity increased by 20% in comparison with the optimal bare gold structure, whilst with respect to phase, sensitivity was approximately two orders of magnitude greater than the bare gold structure. Our results demonstrate that SPR sensors modified with SnSe monolayers could be used in diagnostic applications where both high sensitivity and small concentration of analyte are required.

     

Electroless-plated gold films for sensitive surface plasmon resonance detection of white spot syndrome virus

The paper describes the rapid and label-free detection of the white spot syndrome virus (WSSV) using a surface plasmon resonance (SPR) device based on gold films prepared by electroless plating. The plating condition for obtaining films suitable for SPR measurements was optimized. Gold nanoparticles adsorbed on glass slides were characterized by transmission electron microscopy (TEM). Detection of the WSSV was performed through the binding between WSSV in solution and the anti-WSSV single chain variable fragment (scFv antibody) preimmobilized onto the sensor surface. Morphologies of the as-prepared gold films, gold films modified with self-assembled alkanethiol monolayers, and films covered with antibody were examined using an atomic force microscope (AFM). To demonstrate the viability of the method for real sample analysis, WSSV of different concentrations present in a shrimp hemolymph matrix was determined upon optimizing the surface density of the antibody molecules. The SPR device based on the electroless-plated gold films is capable of detecting concentration of WSSV as low as 2.5 ng/mL in 2% shrimp hemolymph, which is one to two orders of magnitude lower than the level measurable by enzyme-linked immunosorbant assays.     

A Photonic Crystal Fiber Polarized Filter at 1.55 μm Based on Surface Plasmon Resonance

A single-polarization photonic crystal fiber (PCF) based on surface plasmon resonance (SPR) is proposed. Finite element method is employed in simulating the PCF with gold-coated. The resonance wavelength can be modulated by changing the thickness of gold layer. At the resonance wavelength 1.55 μm, the loss of y-polarized mode is much larger than the loss of x-polarized mode. When the fiber length is set to 2 mm, the value of extinction ratio reaches to −118.7 dB, the y-polarized mode is suppressed and only x-polarized mode can be guided. The fiber is applicable in the production of single-polarization filter. The PCF has a simple structure and a big error tolerance, it has a good practicability.

     

Surface plasmon resonance immunosensor for detection of<Emphasis Type="Italic">Legionella pneumophila</Emphasis>

An immunosensor based on surface plasmon resonance (SPR) onto a protein G layer by self-assembly technique was developed for detection ofLegionella pneumophila. The protein G layer by self-assembly technique was fabricated on a gold (Au) surface by adsorbing the 11-mercaptoundecanoic acid (MUA) and an activation process for the chemical binding of the free amine (-NH₂) of protein G and 11-(MUA) using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDAC) in series. The formation of the protein G layer by self-assembly technique on the Au substrate and the binding of the antibody and antigen in series were confirmed by SPR spectroscopy. The surface topographies of the fabricated thin films on an Au substrate were also analyzed by using an atomic force microscope (AFM). Consequently, an immunosensor for the detection ofL. pneumophila using SPR was developed with a detection limit of up to 10² CFU per mL.