Multilayer Surface Plasmon Resonance Research Articles

Simulation and Analysis of a Sub-Wavelength Grating Based Multilayer Surface Plasmon Resonance Biosensor

This paper presents a subwavelength grating based multilayer surface plasmon resonance biosensor (SPRB) which includes a periodic array of subwavelength grating on top of a layer of graphene sheet in the biosensor. The proposed biosensor is named grating-graphene SPRB (GG-SPRB). The aim of the proposed multilayer structure is to improve the sensitivity of the SPRB through monitoring of the biomolecular interactions of DNA hybridization. Significant sensitivity improvement is obtained for the GG-SPRB compared with the conventional SPRB. The result of the numerical investigation of the GG-SPRB is presented and compared with a theoretically developed multilayer matrix formalism, and a good agreement has been observed. In addition, an optimization of the grating dimensions including volume factor, grating depth, grating angle, grating period, and grating geometry (e.g., rectangular, sinusoidal and triangular) is presented. The outcome of the investigation presented in this paper identifies desired functioning conditions corresponding to the best design parameters for the GG-SPRB.

Approach for plasmonic based DNA sensing: amplification of the wavelength shift and simultaneous detection of the plasmon modes of gold nanostructures.

In this article, the detection of DNA hybridization taking advantage of the plasmonic properties of gold nanostructures is described. The approach is based on the amplification of the wavelength shift of a multilayered localized surface plasmon resonance (LSPR) sensor interface upon hybridization with gold nanorods and nanostars-labeled DNA. The amplification results in a significant decrease of the limit of detection from ≈40 nM as observed for unlabeled DNA to 0.2 nM for labeled DNA molecules. Furthermore, the plasmonic band, characteristic of the labeled DNA, is different from that of the LSPR interface. Indeed, next to the plasmon band at around 550 nm, being in resonance with the plasmon band of the LSPR interface, additional plasmonic peaks at 439 nm for gold nanostar-labeled DNA and 797 nm for gold nanorod-labeled DNA are observed, which were used as plasmonic signatures for successful hybridization.

Design and Analysis of a Multilayer Localized Surface Plasmon Resonance Graphene Biosensor

This paper describes a multilayer localized surface plasmon resonance (LSPR) graphene biosensor that includes a layer of graphene sheet on top of the gold layer, and the use of different coupled configuration of a laser beam. The study also investigates the enhancement of the sensitivity and detection accuracy of the biosensor through monitoring biomolecular interactions of biotin-streptavidin with the graphene layer on the gold thin film. Additionally, the role of thin films of gold, silver, copper and aluminum in the performance of the biosensor is separately investigated for monitoring the binding of streptavidin to the biotin groups. The performance of the LSPR graphene biosensor is theoretically and numerically assessed in terms of sensitivity, adsorption efficiency, and detection accuracy under varying conditions, including the thickness of biomolecule layer, number of graphene layers and operating wavelength. Enhanced sensitivity and improved adsorption efficiency are obtained for the LSPR graphene biosensor in comparison with its conventional counterpart; however, detection accuracy under the same resonance condition is reduced by 5.2% with a single graphene sheet. This reduction in detection accuracy (signal to noise ratio) can be compensated for by introducing an additional layer of silica doped B2O3 (sdB2O3) placed under the graphene layer. The role of prism configuration, prism angle and the interface medium (air and water) is also analyzed and it is found that the LSPR graphene biosensor has better sensitivity with triangular prism, higher prism angle, lower operating wavelength and larger number of graphene layers. The approach involves a plot of a reflectivity curve as a function of the incidence angle. The outcomes of this investigation highlight the ideal functioning condition corresponding to the best design parameters.

Optical Properties of Crosslinked Chitosan Thin Film with Glutaraldehyde Using Surface Plasmon Resonance Technique

Problem statement: The aim of this research is to study the optical properties of crosslinked chitosan thin film with glutaraldehyde using Surface Plasmon Resonance (SPR) technique. Approach: The crosslinked chitosan is synthesized by homogeneous reaction of medium molecular weight chitosan in aqueous acetic acid solution with glutaraldehyde as crosslinking agent. Four different amount of chitosan, i.e., 0.40, 0.50, 0.60 and 0.70 g of chitosan, were dissoloved in 50 ml acetic acid separately. Glass cover slips (as substrates) were first coated with two sets of different thickness of gold layer. Then the amount of 0.55 mL of each crosslinked chitosan solution was spin coated onto the gold layer. Results: Using developed multilayer Matlab fitting program (matrix method based), the experimental surface plasmon resonance curves were fitted to obtain the thickness and refractive index of crosslinked chitosan thin film. The real and imaginary part of refractive index of crosslinked chitosan thin film are (1.540 ± 0.005) and (0.015 ± 0.002), respectively. Conclusion: The results are similar for all different thickness of the thin films and not affected by the thickness of gold layer. This study is important for future research on multilayer SPR sensor.

Fibrinogen and lysozyme adsorption on amorphous carbon film surface detected by multilayer device from the back side of the film

To develop hydrogenated amorphous carbon ( a-C:H) as a biocompatible coating, a-C:H was studied in terms of its protein adsorption during the initial process of cell adsorption. A multilayer surface plasmon resonance (SPR) device consisting of an a-C:H layer on Au was built in the Kretschmann configuration to detect protein adsorption on an a-C:H film surface. From the dependence of reflectivity on the laser incident angle, SPR angle was determined to the incident angle in which the light intensity was reduced drastically. The proteins considered were lysozyme (Lyz) and fibrinogen (Fib). The SPR angle increased from 58.09 to 58.69° upon the adsorption of Lyz when the nonadsorbed Lyz was removed after introduction of 20 μM Lyz-containing solution. Upon the adsorption of Fib, the SPR angle increased from 60.95 to 61.76° when the nonadsorbed Fib were removed after the introduction of 0.4 μM Fib-containing solution. The shift in the SPR angle was small for both cases. Obtained results suggested that the number of adsorbed Lyz was higher than that of adsorbed Fib.

Sensitivity of Plasmonic Nanostructures Coated with Thin Oxide Films for Refractive Index Sensing: Experimental and Theoretical Investigations

This paper reports on the use of the Lorentz−Drude model to investigate the refractive index sensitivity, S (change of nanometer per refractive index unit, in nm RIU−1) of multilayered localized surface plasmon resonance (LSPR) interfaces. The investigated interface consists of an array of gold nanostructures (Au NSs) on glass (n1 = 1.51) coated with dielectric overlayers of different refractive index (n2 = 1.45−2.63) and varying thickness (0−300 nm). These interfaces are in contact with solvents of different refractive index (n3 = 1.000−1.630). The refractive index sensitivity for architectures with n1≤ n2 is found to be proportional to the amplitude of the oscillation of the wavelength at maximal absorption (λmax). It reaches its maximal value when the amplitude of the oscillation is maximal and its minimal value when the amplitude is null. The amplitude of the oscillations increases with an increase in refractive index of the dielectric. For n1 > n2, all the curves oscillate in phase leading quickly (ddielectric > 40 nm) to a low value of the sensitivity. Quantitatively, a LSPR architecture of glass/Au NSs/nanocrystalline diamond (n2 = 2.4) with a thickness of 10−20 nm shows the best sensitivity. However, it has to be noted that the sensitivity is mainly affected by the thickness of the dielectric and not by the refractive index of the overcoating

Detection of lysozyme adsorption on titania using surface plasmon resonance on Au layer coated with thin titania film

Titanium metal, which is used as artificial bone, has a titania surface layer. In this study, titania was investigated using surface plasmon resonance (SPR) in terms of protein adsorption, which occurs during the initial process of cellular attachment by employing a multilayer device consisting of a titania layer on Au. The titania film was deposited on the Au layer in the multilayer device by atmospheric chemical vapor deposition. A flow cell was used to evaluate protein adsorption on the titania top layer of the multilayer device. Phosphor buffer solutions with and without the protein lysozyme (Lyz) were injected into the flow cell. From the attenuation of reflected light, the SPR angle was determined as the angle with minimum reflection intensity. The observed behavior of the SPR angle indicated that Lyz was adsorbed on the titania film surface, and the obtained SPR angles increased with the Lyz concentration on the titania surface. These results indicate that the titania/Au multilayer SPR device can easily be used to detect the adsorption of protein.

Short- and Long-Range Sensing Using Plasmonic Nanostrucures: Experimental and Theoretical Studies

The paper reports on the use of the Lorentz-Drude model to investigate the optical behavior of a novel multilayer localized surface plasmon resonance (LSPR) interface. The plasmonic interface consists of a random array of gold nanostructures (Au NSs) formed by thermal deposition of a 4 nm thick gold film on glass, postannealed at 500 °C for 1 min, and coated with two different dielectric layers, silicon dioxide (SiOx) and silicon nitride (Si3N4), of varying thickness. Atomic force microscopy and scanning electron microscopy were used to determine the average size, height, and particle density. The influence of the morphology and interparticle distance on the LSPR characteristics of a glass/Au NSs interface with a constant thickness of a SiOx overcoating was investigated through the calculation of theoretical transmission spectra. Ajusting the theoretical curve to experimental LSPR spectra allowed the geometry of the plasmonic interface to be fixed and evaluation of the change in the wavelength at maximum ...

Effects of intermediate dielectric films on multilayer surface plasmon resonance behavior

The effects of intermediate dielectric films on multilayer surface plasmon resonance (SPR) behavior were studied in terms of biosensing applications. Ten simple and complex oxides and fluoride, including MgF 2 and MgO, SiO 2, TiO 2 and complex PZT family dielectric materials, were evaluated. The materials cover a wide range of refractive indices, from 1.19 for the porous silica film to 2.83 for the TiO 2 film. The resonance curves of the multilayer SPR configurations were taken from an angular modulated Kretschmann set-up under a fixed incident wavelength of 543.5 nm. The intermediate dielectric layer has no strong effect on the SPR resonance angle and minimum reflectance at the resonance point. Some intermediate dielectric films, such as MgF 2, porous silica, TiO 2 and PLZT, apparently reduce the width of the resonance curves, resulting in sharper resonance dips. Better performance of the multilayer SPR biosensor incorporating these dielectric films is expected.

Admittance loci design method for multilayer surface plasmon resonance devices

Dielectric mirror types of multilayer structures have been applied to enhance the performance of surface plasmon resonance (SPR) devices. It demands a more robust design method than traditional Fresnel's equations. An admittance locus is a kind of optical thin film design method which has been extensively used for high performance optical coatings. We have applied this method for the design of multilayer SPR devices, including symmetric (glass|Au(40 nm)–[TiO 2(20 nm)–SiO 2(20 nm)] 4–Au(30 nm)) and asymmetric (glass|Ag(50 nm)–[TiO 2(20 nm)–SiO 2(20 nm)] 4–Au(20 nm)) structure. It provides a much necessary guidance for the choices of suitable optical materials, thickness, and number of layers for the intended SPR performance. With a 633 nm light source and a BK7 coupling prism under water, one can shift the resonant angle toward the critical angle and have smaller half maximum band widths (HMBW) at (64°, 2°) and (61.52°, 0.25°) for symmetric and asymmetric designs, respectively.

광학 어드미턴스 기법과 진화 알고리즘 기법을 이용한 다층 표면 플라즈몬 공명 센서의 설계

This paper describes the optimal design of a multi-layered surface plasmon resonance sensors to meet various specifications and improve some physical parameters. Dip 3 dB bandwidth and depth were chosen as design parameters and the objective function was the norm of the difference between design parameters and target values. The design variables are thicknesses of each layer and to obtain the design parameters, the optical admittance method was employed. The (1+1) evolution strategy was employed as an optimization tool. By applying the proposed optimization procedure to a 3-layered sensor, the optimized design variables considerably improved the 3 dB bandwidth by 4.8 nm and the dip depth by 1.1 dB.

A new surface plasmon resonance sensor for high-throughput screening applications

We report a new high-throughput surface plasmon resonance (SPR) sensor based on combination of SPR imaging with polarization contrast and a spatially patterned multilayer SPR structure. We demonstrate that this approach offers numerous advantageous features including high-contrast SPR images suitable for automated computer analysis, minimum crosstalk between neighboring sensing channels and inherent compensation for light level fluctuations. Applications of a laboratory prototype of the high-throughput SPR sensor with 108 sensing channels for refractometry and biosensing are described. In refractometric experiments, the noise-limited refractive index resolution of the system has been established to be 3 x 10(-6) refractive index unit (RIU). Experimental data on detection of human choriogonadotropin (hCG) suggest that in conjunction with monoclonal antibodies against hCG, the reported SPR imaging sensor is capable of detecting hCG at concentrations lower than 500 ng/ml.

Sensitivity evaluation of a multi-layered surface plasmon resonance-based fiber optic sensor: a theoretical study

A multi-layered surface plasmon resonance (SPR)-based fiber optic absorption sensor has been studied theoretically. The sensitivity is evaluated for the p-polarized light launched in the fiber using ray approximation. Four-layers configuration is used to excite the surface plasmon wave. The first layer or the medium considered is the core of the fiber. Second and third layers are metallic (silver and gold). The fourth layer or medium is absorbing medium. The effect of the ratio of the thickness of the metallic layers (silver:gold) on the sensitivity of the sensor has been investigated. The sensitivity increases as the silver to gold thickness ratio increases. The gold should be used only to protect silver layer. In addition, the influences of various parameters like numerical aperture (NA), ratio of sensing region length to fiber core diameter, total bimetallic thickness, maximum absorption wavelength, and half maximum width of the sensing medium on the sensitivity of the sensor have been studied. It has been found that the sensitivity is better for the lower off-resonance excitation frequency. Replacing gold by self-assembled monolayers like thiol does not improve sensitivity much. Further, adding ZrO 2 as the fourth layer does not improve the sensitivity of the four layers configuration.

Multi-layer Si-Based Surface Plasmon Resonance Structure for Absorption Sensing

A multi-layer Si-based surface plasmon resonance (SPR) sensing structure, consisting of a silicon coupling prism, an intermediate SiO2 layer, a gold film, and a sensing medium, is considered. Such structure makes possible an excitation of two angularly separated surface plasmon polariton modes over both sides of the gold film. We examine the response of the system in the case of the absorption sensing, which is simulated by the gold thickness change. Both calculations and experimental data show that the “internal” plasmon mode over the SiO2/gold interface appears to be at least 4–6 times more sensitive than the “external” one over the gold/sensing medium interface, which is employed in most conventional SPR schemes. The proposed internal plasmon-based absorption sensor structure can be used for studies of optical absorption layers and for colloidal Au-enhanced SPR sensing of ultra-small (bio)-chemical agents.

Multilayer system for a high-precision surface plasmon resonance sensor

A multilayer surface plasmon resonance system was designed for high-precision chemical sensor applications. In this sensor, the angular distribution of reflectance from a thin metal film-which is in contact with a sample-is measured. An absorption peak is observed whose angular distribution of reflectance, owing to the excitation of surface plasmon resonance, is measured. The refractive index of the sample is determined from this peak angle. The resolution limit for refractive-index measurements is determined by the absorption peak width. We describe a multilayer system in which an additional layer is added to the conventional Kretschmann geometry; as a result, peak widths are significantly reduced. The angular distribution of reflectance is calculated using Fresnel's formulas and multiple-reflectance theory in order to understand the effect of thickness and refractive index of the additional layer. By optimizing the thickness of the layer, peak widths are reduced to approximately one third of that obtained using the Kretschmann geometry. Experimental results demonstrate the feasibility of this approach.