Surface Plasmon Resonance Curve Research Articles

Surface plasmon based sensor with order-of-magnitude higher sensitivity to electric field induced changes in dielectric environment at metal/nematic liquid-crystal interface

A highly sensitive surface plasmon based sensor is developed for monitoring changes in the dielectric environment at metal/dielectric interfaces. It consists of high-index prism/30–40nm gold/nematic liquid crystal (E44)/indium-tin-oxide/glass structure, which enables measurements of surface plasmon resonance (SPR) curves by using the Kretschmann configuration. The baseline sensitivity of the device to changes in the refractive index is evaluated by using Au/air, Au/water, and Au/nematic liquid crystal (E44); the measured baseline sensitivity is in excellent agreement with theoretically predicted optimal sensitivity. The sensitivity of the device to electric field induced changes in the refractive index of the material at the interface, however, is 28-times higher than previously known value for a similar sensor. Effects related to the periodic alignment of the liquid crystal on gold surface and surface plasmon mediated diffraction are investigated.

Dielectric Properties of SnO2 Thin Film Using SPR Technique for Gas Sensing Applications

Focus has been made on the determination of dielectric constant of thin dielectric layer (SnO2 thin film) using surface plasmon resonance (SPR) technique and exploiting it for the detection of NH3 gas. SnO2 thin film has been deposited by rf-sputtering technique on gold coated glass prism (BK-7) and its SPR response was measured in the Kretschmann configuration of attenuated total reflection using a p-polarised light beam at 633 nm wavelength. The SPR response of bilayer film was fitted with Fresnel’s equations in order to calculate the dielectric constant of SnO2 thin film. The air/SnO2/Au/prim system has been utilized for detecting varying concentration (500 ppm to 2000 ppm) of NH3 gas at room temperature using SPR technique. SPR curve shows significant shift in resonance angle from 44.8° to 56.7° on exposure of fixed concentration of NH3 gas (500 ppm to 2000 ppm) with very fast response and recovery speeds.

Design of a silicon-based plasmonic optical sensor for magnetic field monitoring in the infrared

Surface plasmon resonance (SPR) sensor chip is proposed for magnetic field monitoring in the infrared wavelength region. The structure is based on silicon substrate and gold as SPR-active metal used with an appropriate magnetic fluid film. The angular interrogation method has been used to study the sensor’s performance in terms of large shift and small width of the SPR curve for a wide range of magnetic field between 30 and 220 Oe. The effect of field incidence angle is also studied on the proposed sensor’s performance, and it is observed that the field should be incident as parallel to the magnetic fluid surface as possible. Any possibility of oxidation problem to the proposed SPR sensor is addressed by using a stable buffer layer. All the performance parameters were found to be significantly large for the above field incidence condition. The proposed sensor is able to achieve a resolution of the order as high as 0.18 Oe for magnetic field detection.

A novel algorithm based on the coefficient of determination of linear regression fitting to automatically find the optimum angle for miniaturized surface plasmon resonance measurement

We developed a novel algorithm which can automatically find the optimum angle for surface plasmon resonance (SPR) measurements based on fixed angle mode using MATLAB R2013a. The optimum angle is decided by the coefficient of determination of linear regression fitting on an SPR curve obtained from a miniaturized SPR system. The SPR biosensor based on the novel algorithm achieved a dynamic range of 0.00696RIU of and LOD of 3.1956×10−6.

Surface plasmon induced enhancement with magneto-optical layer

In this study, we examined surface plasmon resonance (SPR) induced magneto-optical (MO) Kerr signals, and obtained a complete SPR curve in multilayered metallic structures comprising 6-nm-thick Au, t-nm-thick Permalloy (Py), and 26-nm-thick Au layers (with various thicknesses of Py). As the thickness of the Py layer increased, the SPR weakened. The MO signals were exhibited to various magnitudes of amplification while measuring the hysteresis loop at different segments of the SPR curve, which were the product of the MO Kerr effect. The MO signals between the reflectance maximum and reflectance minimum of the SPR were enhanced significantly in the samples with a 2 to 20-nm-thick Py layer. After measuring and analyzing the MO signals from multiple specimens with various thicknesses of Py, the optimal thickness of the Py layer was 10 nm, at which the strongest signal amplification was obtained.

Investigation of surface plasmon resonance phenomena by finite element analysis and Fresnel calculation

In this study, a novel simulated method was developed to provide a graphical and simplistic simulation technique for the purpose of enhancing feasibility of classical surface plasmon resonance (SPR) experiment. Winspall, the software based on the Fresnel equations and the matrix formalism was used to compute the reflectivity of optical multilayer systems. In a simulation study, SPR curves were plotted using Winspall with ultrapure water, 50% ethanol aqueous solvent and pure ethanol as the environmental media. SPR angles of 67.1°, 71.7° and 72.5° were obtained, respectively. These values displayed significant disparity from the experimental data of 62.7°, 65.1° and 65.3° under the same conditions. Finite element analysis (FEA) was then evaluated for its suitability as a better alternative method. By establishing a new Kretchmann SPR model and simulating the S11 parameters, the obtained SPR angles of 62.6°, 65.0° and 65.3° agreed well with the experimental results. Thus FEA method was a more feasible alternative based on our experimental conditions. Hence, an optimal methodology for the theoretical study of SPR detection was developed in this study which contains port boundary conditions, background filed and period boundary conditions. More importantly, this study has established a new avenue of SPR chip applications for portable SPR devices.

Magneto-optical properties of BiFeO3 thin films using surface plasmon resonance technique

Indigeneously assembled surface plasmon resonance (SPR) set up has been exploited to study the magnetic field dependent optical properties of BiFeO3 thin films. BiFeO3 thin films have been deposited onto gold (Au) coated glass prism by using pulsed laser deposition technique. The surface plasmon modes in prism/Au/BiFeO3/air structure have been excited in Kretschmann configuration at the interface of Au/BiFeO3 thin films. The SPR reflectance curves obtained for prism/Au/BiFeO3/air structure were utilized to investigate the optical properties of BiFeO3 thin films at optical frequency (λ=633nm) as a function of applied magnetic field. SPR curves shows a continuous shift towards lower angles with increasing applied magnetic field, which indicate the promising application of ferromagnetic BiFeO3 film as a magnetic field sensor. Complex dielectric constant of deposited BiFeO3 film was determined by fitting the experimental SPR data with Fresnel׳s equations. The variation of complex dielectric constant and refractive index of BiFeO3 film was studied with increase in magnetic field, and the sensitivity of magnetic field sensor was found to be about 0.52RIU/T.

How to avoid a negative shift in reflection-type surface plasmon resonance biosensors with metallic nanostructures

We experimentally demonstrate that introduction of a dielectric film can prevent the surface plasmon resonance (SPR) curve from being shifted to a smaller angle, called negative shift, which occurs unpredictably when metallic nanostructures deposited on a metal film are exposed to an adsorption of binding analytes. From parylene coating experiments, we find that the proposed reflection-type SPR system with a low refractive index MgF2 film and gold nanorods can provide an enhanced sensitivity by more than 6 times as well as a reliable positive shift. It is due to the fact that use of a dielectric film can contribute to the compensation of an anomalous dispersion relation and the prevention of a destructive interaction of propagating surface plasmons with multiple localized plasmon modes. Our approach is intended to show the feasibility and extend the applicability of the proposed SPR system to diverse biomolecular reactions.

Magneto-Optical Kerr Effect Enhanced by Surface Plasmon Resonance and Its Application on Biological Detection

We investigated the magneto-optical Kerr signals enhanced by surface plasmon resonance (SPR) and its application of the biomolecular detection. We measure the SPR curve obtained in multilayered metallic structures (t nm Co/45 nm Au) with varying cobalt thickness t. The thicker cobalt layer causes the weaker SPR. The magneto-optical signals also receive different magnitude of amplification due to measuring the hysteresis loop on different segments of the SPR curve via magneto-optical Kerr effect (MOKE). It also worth noticing that the magneto-optical signals from the reflectance maximum or reflectance minimum of SPR would be enhanced significantly, if the thickness of Co is within the range of 3 to 28 nm. By measuring and analyzing the magneto-optical signals from samples with different thicknesses of Co, we determined an optimal thickness of 8 nm where the signal amplification is the largest. In biomedical applications, this combined system is able to lead as a sensitive biomolecule sensing. We have verified the feasibility via fetal bovine serum (FBS) attached.

Determination of the Optical Thickness of sub 10-nm Thin Metal Films by SPR Experiments

We discuss the experimental data of surface plasmon resonance (SPR) occurring at the interface between air and single and bimetallic thin layers of Au and Ag prepared on glass substrates. The bilayer configuration allowed for the measurements of the optical constants of metallic films that are ultra thin; e.g., below 10 nm of thickness since SPR modes on such thin films in a single-layer configuration are shallow. We also discuss the effect of film thickness on SPR coupling. Thickness and refractive index of the films were determined by matching experimental SPR curves to the theoretical ones. Thickness and roughness of the films were also measured by atomic force microscopy. The results obtained by experimental measurements are in good agreement with AFM analysis.

Label-Enhanced Surface Plasmon Resonance: A New Concept for Improved Performance in Optical Biosensor Analysis

Surface plasmon resonance (SPR) is a well-established optical biosensor technology with many proven applications in the study of molecular interactions as well as in surface and material science. SPR is usually applied in the label-free mode which may be advantageous in cases where the presence of a label may potentially interfere with the studied interactions per se. However, the fundamental challenges of label-free SPR in terms of limited sensitivity and specificity are well known. Here we present a new concept called label-enhanced SPR, which is based on utilizing strongly absorbing dye molecules in combination with the evaluation of the full shape of the SPR curve, whereby the sensitivity as well as the specificity of SPR is significantly improved. The performance of the new label-enhanced SPR method was demonstrated by two simple model assays: a small molecule assay and a DNA hybridization assay. The small molecule assay was used to demonstrate the sensitivity enhancement of the method, and how competitive assays can be used for relative affinity determination. The DNA assay was used to demonstrate the selectivity of the assay, and the capabilities in eliminating noise from bulk liquid composition variations.

N-doped ZnO thin film for development of magnetic field sensor based on surface plasmon resonance

Magnetic-field-dependent optical properties of nitrogen-doped ZnO (ZnO:N) thin films were investigated using surface plasmon resonance (SPR) and a highly sensitive (4.65/Tesla) magnetic field sensor has been realized. The refractive index (RI) of ZnO:N film increases from 1.949 to 2.025 with increase in N doping from 0% to 10% demonstrating tunable RI. In contrast to pure ZnO, SPR curves for ZnO:N films exhibit a shift toward lower angles with increasing applied magnetic field from 0 to 35mT due to change in reflectance of light upon reflection from ferromagnetic surface. Results indicate promising application of ferromagnetic ZnO:N film as a magnetic field sensor.

Optical determination of thick graphene layer number based on surface plasmon resonance

An optical method of measuring the number of layers in a graphene sample is formulated and compared with the conventional surface plasmon resonance (SPR) detection scheme, the latter being appropriate only for a very few graphene layers. Numerical results based on transfer-matrix method support that an alternative method, wherein the SPR substrate includes a dielectric overlayer, is feasible over a wide range of graphene layer numbers. While the multilayer graphene may lead to a broad and shallow SPR curve owing to the nonzero imaginary part in its relative permittivity, the dielectric overlayer makes the resonant surface plasmons less affected by graphene, resulting in a strong and deep absorption band at resonance. Linear regression analysis shows that the measurable graphene layer number can be as high as 50.

Analysis of cell surface antigens by Surface Plasmon Resonance imaging

Surface Plasmon Resonance (SPR) is most commonly used to measure bio-molecular interactions. SPR is used significantly less frequent for measuring whole cell interactions. Here we introduce a method to measure whole cells label free using the specific binding of cell surface antigens expressed on the surface of cancer cells and specific ligands deposited on sensor chips using an IBIS MX96 SPR imager (SPRi). As a model system, cells from the breast cancer cell line HS578T, SKBR3 and MCF7 were used. SPRi responses to Epithelial Cell Adhesion Molecule (EpCAM) antibody and other ligands coated on the sensor chips were measured. SPR curves show a response attributable to the sedimentation of the cells and a specific binding response on top of the initial response, the magnitude of which is dependent on the ligand density and the cell type used. Comparison of SPRi with flow cytometry showed similar EpCAM expression on MCF7, SKBR3 and HS578T cells.

Design of a plasmonic optical sensor probe for humidity-monitoring

High performance surface plasmon resonance (SPR) sensor is proposed for relative humidity (RH) monitoring. The structure is based on widely used 2S2G chalcogenide glass and gold as SPR active metal applied with silica-based porous film. The angular interrogation method has been used to study the performance of the sensor in terms of intrinsic sensitivity (SI) that includes the width and shifts of SPR curve for the entire RH-range between 0% and 100%. The effect of temperature is also studied on the proposed sensor's performance. Any possibility of oxidation problem to the proposed SPR sensor due to constantly being in contact with humid environment may be addressed by using a stable buffer layer. Intrinsic sensitivity of the proposed sensor is significantly high for almost entire range of RH values. The proposed sensor has a good resolution of the order of 10−2% RH.

Low-cost, high performance surface plasmon resonance-compatible films characterized by the surface plasmon resonance technique

A new analytical method based on the surface plasmon resonance (SPR) technique is presented, with which SPR curves for both wavelength and angular modulations can be obtained simultaneously via only a single scan of the incident angle. Using this method, the SPR responses of TiO2-coated Cu films are characterized in the wavelength range from 600 nm to 900 nm. For the first time, we determine the effective optical constants and the thicknesses of TiO2-coated Cu films using the SPR curves of wavelength modulation. The sensitivities of prism-based SPR refractive index sensors using TiO2-coated Cu films are investigated theoretically for both wavelength and angular modulations, the results show that in the case of sensitivity with wavelength modulation, TiO2-coated Cu films are not as good as the Au film, however, they are more suitable than the Au film for SPR refractive index sensors with angular modulation because a higher sensitivity can be achieved.

Electrical conductivity properties of boron containing Langmuir–Blodgett thin films

Electrical characterisations of Mesitylene-2-boronic acid (MBA), Phenylboronic acid (PBA) and 1-Naphthylboronic acid (NBA) are investigated using C-f and I–V measurements. All materials are used to fabricate Langmuir–Blodgett (LB) thin film by vertical dipping method. Metal/LB film/Metal sandwich structure is prepared to investigate electrical properties of boron containing LB films. For evaluation of electrical measurements, the theoretical thickness is determined using ChemDraw software and experimental thickness value is calculated from surface plasmon resonance (SPR) curves. Dielectric measurements are used to determine the dielectric constant (e) and to compare refractive index value which is determined from SPR results. The values of e are determined as 2.79, 2.70, 2.82 for MBA, PBA and NBA respectively. The refractive indexes of three materials are calculated to be around 1.6. I–V results are used to study the conduction mechanism of these LB films. The low voltage region shows an ohmic characteristic for each LB film and conductivity values are calculated as 0.55 × 10−11 S m−1, 0.42 × 10−11 S m−1 and 3.62 × 10−11 S m−1 for MBA, PBA and NBA respectively. In the high voltage region of I–V curves that show Schottky type conduction mechanisms with the barrier heights estimated for each LB film as 0.77, 0.79 and 0.76 eV respectively.

Effect of prism material on design of surface plasmon resonance sensor by admittance loci method

A theoretical study on the design of surface plasmon resonance (SPR) based sensor by admittance loci method has been reported in this paper with the main emphasis being given to the effect of the prism material in a conventional Kretschmann structure in attenuated total internal reflection (ATIR) mode. Several sensing media such as water, acetone, methanol etc have been investigated using different types of prism materials to study their effect on SPR sensing and validated by corresponding admittance loci plots as well as respective SPR curves. The performance of the sensor based on choice of the prism material has been discussed with the help of sensitivity plots giving due to the importance of dynamic range of the designed sensor. Simulations have been carried out in MATLAB 7.1 environment.

Experimental characterization of contaminants in engine lubricants using surface plasmon resonance sensing

Purpose – The purpose of this paper is to develop new knowledge in experimental characterization of contaminants in engine lubricants, using surface plasmon resonance (SPR) sensing that can be applicable for on‐line condition monitoring of lubricant quality and engine component performance.Design/methodology/approach – The effect of change in optical properties (e.g. transparency, absorption, and refractive index) of engine lubricants caused by the introduction of contaminants, such as gasoline, coolant, and water, on the surface plasmon resonance characteristics is analyzed experimentally. In SPR measurement, variations in both the refractive index and absorption cause changes in the SPR curve, which is the dependence of reflectivity vs incidence angle. The SPR characteristics (e.g. refractivity) of engine lubricant contaminated by gasoline, water and coolant at different concentration are measured as a function of resonance angle and analyzed with respect to different concentration (1%‐10%) of contamina...

聚合物波导型表面等离子体共振传感器的特性研究

A polymer waveguide sensor was designed based on the theory of surface plasmon resonance(SPR).The sensor with SU-8 polymer as the waveguide core material is fabricated on a silicon substrate with a under cladding layer of PMMA.Effect of refractive index of polymer,refractive index of analyte,the different metal,and the thickness of metal on SPR curve is analyzed.Theoretical analysis results show that the sensor sensitivity is improved with the refractive index of analyte increase.The resonance wavelengths of SPR sensor move to longwave direction when the refractive index of polymer is low,and its detection range trend to move to long refractive index.Otherwise the results are contrary.