Surface Plasmon Resonance Resonance Angle Research Articles

Controlling photonic spin Hall effect based on tunable surface plasmon resonance with an N−type coherent medium

We propose a scheme to control the spin Hall effect (SHE) of light reflected from a Kretschmann configuration containing an N-type coherent atomic medium. Owing to the excitation of surface plasmon resonance (SPR), enhanced spin splitting occurs in the reflection dip for TM-polarized incident light. The magnitude and sign of the transverse shifts of spin components depend on the system internal damping which is closely related to the absorption coefficient of atoms. There is an optimal absorption around which the spin components undergo large transverse displacements. We also show that the direction of the photonic spin accumulations can be switched between positive and negative values by adjusting the system parameters. In addition, the resonance angle of SPR varies linearly with the refractivity of the medium. We can therefore coherently control the peak position of the transverse shift. Compared to the conventional SPR-based systems, the proposed scheme provides a more flexible pathway for manipulating and enhancing the SHE of light without changing the structure. This tunable SHE may find applications in spin photonic devices.

Novel high sensitivity SPR sensor based on surface plasmon resonance technology and IMI waveguide structure

Surface plasmon resonance (SPR) technology features convenient and rapid detection and high sensitivity; it does not need to mark samples and can maintain molecular activity. In this study, we investigate the symmetrical IMI waveguide structure of glass–silver film–ethanol and realize the high sensitivity of the SPR sensor in a low-temperature environment. We determined the relationship between the change in ethanol temperature and SPR resonance angle via the relationship between the refractive index of the liquid sensing material and the ambient temperature. Results show that the SPR sensor transmittance is as high as 95%. As the temperature increases, the resonance angle of the new Kretschmann configuration decreases, which is suitable for low-thermal sensing. Changing the proportion of the ethanol solution structure has no effect on the resonance phenomenon. The sensitivity of the sensor reaches −0.408°/°C. The device can effectively improve the accuracy and anti-interference ability of the angle scanning SPR sensor and has good application and promotion value.

Table top surface plasmon resonance measurement system for efficient urea biosensing using ZnO thin film matrix.

The present report addresses the application of surface plasmon resonance (SPR) phenomenon for urea sensing. The former promises a high sensitivity, label-free detection, and real-time information by monitoring the refractive index change at the metal–dielectric interface. In the present report, a highly sensitive urea biosensor has been developed by integrating a ZnO thin film matrix with the SPR technique. Kretschmann configuration has been used to excite the surface plasmon (SP) modes at the ZnO–metal (gold) interface using an indigeneously developed table top SPR measurement setup. Urease (Urs), the urea-specific enzyme, has been immobilized on the surface of ZnO thin film by physical adsorption technique. The SPR reflectance curves were recorded for the prism/Au/ZnO/Urs system in angular interrogation mode with phosphate-buffered saline (PBS) solution as the liquid media. The SPR resonance angle is found to be shifted toward a lower angle from 49.1 to 42.0 deg with an increase in the urea concentration (0 to 300 mg/dl) in the PBS solution. The developed sensor (prism/Au/ZnO/Urs) is found to be highly sensitive [sensitivity=0.039 deg/(mg/dl) or 203 deg/RIU] with detection accuracy of 0.045(deg)(−1).

Sensitive optical biosensor based on surface plasmon resonance using ZnO/Au bilayered structure

The present article represents the preparation of highly sensitive optical biosensor using an indigenously assembled table top Surface plasmon resonance (SPR) technique. Surface plasmon modes have been excited at the ZnO-gold interface exploiting Kretschmann configuration. RF-magnetron sputtering has been utilised to deposit ZnO thin films further used for the immobilization of specific enzyme GOx by physical adsorption technique. The SPR reflectance curves were recorded for the GOx/ZnO/Au/prism system in angular interrogation mode in Phosphate buffer saline (PBS) solution by varying analyte (glucose) concentration from 0mg/dl to 300mg/dl. The transient variation in the intensity of reflectance (i.e. response) at fixed SPR resonance angle for increasing concentration of glucose is also reported. The prepared sensor exhibits enhanced response (0.75 for 25mg/dl) with high specificity and good linearity beyond the physiological range indicating the realization of an efficient optical biosensor.

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.

An improved dispersion law of thin metal film and application to the study of surface plasmon resonance phenomenon

The dispersion law of metal film based on the Drude׳s free-electron theory is improved by employing the Fuchs–Sondheimer theory. In the new law, the thickness and surface roughness are taken into account to describe theoretically the dispersion of thin metal films. Then the improved model is used to analyze the surface plasmon resonance (SPR) of gold films. The results indicate that the thickness and surface roughness of gold film affect the resonance properties significantly. Specifically, when the film thickness is getting close to the electron mean-free-path (MFP), there is no obvious SPR phenomenon. In addition, the surface roughness of metal film can change the resonance angle of SPR. When the surface becomes smooth, resonance angle of SPR will decrease. It means that, for a certain metal the effects of film thickness and surface roughness should be considered in SPR technique.

Ultraslow relaxation of the structure at the ionic liquid|gold electrode interface to a potential step probed by electrochemical surface plasmon resonance measurements: asymmetry of the relaxation time to the potential-step direction

The relaxation of the structure in the electrical double layer at the ionic liquid|gold interface to the steps of the electrode potential has been studied using surface plasmon resonance (SPR) measurements. The relaxation of the SPR resonance angle occurs on the order of 100 s, which is distinctively slower than the RC time constant of the cell, about 0.1 s. A relaxation model considering the distribution of the time constants well reproduces the SPR curves. The potential steps to the positive direction lead to two orders of magnitude slower relaxation of the SPR resonance angle than those to the negative direction. The ultraslow relaxation and its asymmetry to the potential-step directions are likely to be caused by slow inter-layer dynamics of ions in the ionic multilayers and interaction of ions with gold, respectively.

Real-Time Visualization Method of Surface Plasmon Resonance with Spectroscopic Attenuated Total Reflection

AbstractWe report the real-time visualization method of surface plasmon resonance with the spectroscopic attenuated total reflection. Recently, surface plasmon resonance (SPR) had been studied for plasmonics devices to construct faster processor in the electronic microprocessors. SPR is strong interaction between light and free electron near metal surface, which cause absorption of light due to its resonance. The behavior can be explained with Fresnel’s equation. As the wave number of light with a certain frequency is not matched with that of surface plasmon, a prism or a grating is used in order to compensate this mismatching. In the prism case, the wave number is changed by changing the incident angle to the metal surface inside the prism as ksp=n*k0sinθ, where ksp and k0 is the wave numbers of surface plasmon and incident light, respectively, n is the refractive index of the prism and θ is the incident angle to the metal surface inside the prism. Therefore, the SPR can be observed by absorption of light as functions of the wavelength and the incident angle. This resonance behavior as functions of the wavelength and the incident angle can be observed directly with a two-dimensional detector such as a CCD camera. As the two-dimensional SPR images for 50nm-thick silver films on the prism surface have been observed experimentally, they have good agreement with calculated ones. Kretchmann configuration using a glass prism and an approximately 50-nm-thick silver or gold film was often used in order to evaluate the optical constants of the film. Most of SPR signals had been measured with either angular or spectral dependence with this geometry. In the case of angular dependence, the monochromatic laser, e.g. He-Ne laser at 632.8nm, is often used for the incident light. One can measure reflection loss as a function of an incident angle in the total reflection region. Increase in the resonance angle of SPR is well known when the thin oxide film on the metal film. The two-dimensional image of SPR is called “surface plasmon spectral fingerprint”, because it can inform conditions of metal films whether they are reacted or oxidized. Many fingerprints are expected by changing the thickness of the coating layer on the silver surface. In our method, thin metal film on a prism was excited by focusing beam of white light. SPR was clearly visualized with a spectrometer equipped with a two-dimensional CCD detector in the coordination of the incident angle and the wavelength. Various metal films could be distinguished even in partially oxidized condition. This real-time SPR visualization method would be useful not only for monitoring of surface reaction but for fabricating plasmonic devices.

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.

Effects of solute–matrix interaction on monitoring the conformational changes of immobilized proteins by surface plasmon resonance sensor

A real-time and labeling-free surface plasmon resonance (SPR) sensor was used to monitor the conformational changes of immobilized globule proteins (RNase A and lysozyme) in chemical unfolding and refolding. The effects of chemical denaturants on the protein structures were investigated. The methodology in protein conformational study on the solid surface is refined through the theoretic calculations and the conformational information of native/denatured proteins in solution. Additionally, our observation illustrates that the ambient buffer solution is merit to influence the refractive index of immobilized protein films and directly be observed from the SPR resonance angle shifts.

Application of an absorption-based surface plasmon resonance principle to the development of SPR ammonium ion and enzyme sensors.

Two new types of surface plasmon resonance (SPR) sensors that can determine the concentration of ammonium cations and urea were realized based on the previously reported theory of the absorption-based SPR measurement method. The change of the dielectric constant caused by the change of the light absorption characteristics of dyes incorporated in a sensing membrane phase is utilized in these SPR sensors. The determination of ions using the SPR sensor was realized by detecting the SPR signals of the minimum reflectance related to the change of absorption spectra of the dye in the ion optode membrane consisting of an ammonium-selective ionophore (TD19C6) and a lipophilic cationic dye (KD-M11) that shows absorption spectral changes due to protonation and deprotonation. A SPR enzyme sensor that can determine the concentration of urea was prepared by the combination of this ion optode membrane and an enzyme membrane based on urease. With the newly developed SPR sensors, the intensity changes of the reflectance at the fixed SPR resonance angle are monitored, which is different from conventional SPR sensors where usually the change of the SPR resonance angles is detected. In a continuous-flow experiment using the SPR ion sensor for NH4+ ion determination, a dynamic measurement range from 10(-5) to 10(-2) M was achieved. In the case of the enzyme-based SPR urea sensor, a dynamic range from 10(-4) to 10(-1) M was observed in a stopped-flow batch arrangement. It is expected that this sensing technique can be applied for the SPR-based detection of a wide range of low molecular weight analytes.

Molecular Motion of Electrically Stimulated Self-Assembled Monolayers on Gold Surface

The molecular motion of self-assembled monolayers (SAMs) on gold was examined using surface plasmon resonance (SPR) under an electric field. Electrically stimulated SAMs are generated from asymmetric disulfides containing a cyano−fluoro−terphenyl moiety that has a large anisotropic factor of the dipole moment. SPR was combined with a liquid crystal (LC) cell, which only detects a strong influence of the electric field on SAMs. A slight change in the SPR angle was observed upon the application of an electric field in the cell. The response time to saturation of the change of the SPR resonance angle is approximately 150 ms, which is not as fast as those of conventional liquid crystal materials. Furthermore, the relaxation time is much slower than in the case of a conventional liquid crystal cell. This is the first demonstration of an electrically induced motional behavior of a SAM that is chemically attached to a gold surface.

Nanometer indicating system based on surface plasmon resonance and its application in an interferometer

A novel method for nanometer indicating based on surface plasmon resonance (SPR) is introduced. A fiber probe with a semispherical end approaching a coated Kretschmann (1971) prism is equivalent to a four-layer prism-metal-air-fiber structure. Theoretical analysis shows that the transmitted intensity coupling into the fiber probe changes as the thickness of the air gap varies. Owing to this property, a noncontact nanometer indicating system can be built. The SpR nanometer indicator can be integrated into a heterodyne interferometer to reduce drift. Askew retroreflector is designed so that the incident angle of its first reflection surface is equal to the resonance angle of SPR to implement the integration SPR indicating experiments show that a maximum deviation of 12 nm and a resolution of 0.1 nm/nV can be achieved. Moreover, the uncertainty of an integrated interferometer whose optical path difference is 300 mm is reduced from 60 to 10 nm when air-conditioning is 0.5 °C/h.

Surface plasmon resonance enhanced optical absorption spectroscopy for studying molecular adsorbates

We present an automated setup to measure the surface plasmon resonance (SPR)-enhanced optical absorption spectra of molecular adsorbates. The setup detects the reflectivity at the SPR resonance angle as a function of the incident light wavelength. Because the resonance angle is wavelength dependent, a feedback mechanism adjusts the photodetector position to follow the resonance angle when the wavelength varies. Both theoretical calculations and experimental measurements show a signal enhancement of up to ∼40 times over the conventional absorption spectroscopy. The SPR-based absorption spectroscopy is surface specific because the optical field is localized near the surface at resonance. In addition, the SPR angular shift is simultaneously measured, which provides adsorbate coverage and adsorption kinetic information. We anticipate that with our automated system, the method could be used in the study of adsorbed molecules and in chemical and biosensor applications.

Characterization of surface plasmon resonance biosensor

In the present work we present a simple method for analyzing the surface plasmon resonance (SPR) spectra numerically. According to our calculation, we found that the shift of the resonance angle is proportional to the surface density of the adsorbed molecular layer and the value difference between the refractive index of the protein layer and that of the buffer. The variation of the thickness of the gold film may change the resonance angle but does not affect the linear correlation of the shift of the resonance angle with the surface density of the adsorbed protein. In addition, we found that the variation of the thickness of the cover slide, which is stuck to the base of the prism and which is covered by a thin gold film, is approximately not influenced by the resonance angle of SPR.