Surface plasmon resonance sensor based on diffraction grating with high sensitivity and high resolution

A surface plasmon resonance (SPR) sensor based on diffraction grating with high sensitivity and high resolution is proposed. The sensitivity of grating coupled SPR sensor based on angular interrogation is enhanced by replacing +1st diffraction order of metallic grating with −1st diffraction order to excite the surface plasmon. To improve the resolution of grating-based SPR sensor, aluminum is used as an SPR-active metal. The reflectivity dip of the Al-based sensor is sharper than an Au-based one, which is the mostly widely used as SPR-active metal. And 3-nm-thick gold film is deposited on the grating surface in order to protect the Al layer from getting oxidized. Numerical simulations show that the sensor not only has high sensitivity and high resolution, but also exhibits good linearity.     

Numerical simulation of wavelength-modulated surface plasmon resonance-based fiber optic sensor

A systematically theoretical analysis of a surface plasmon resonance (SPR)-based optical fiber sensor is carried out. A three-layer mode (fiber core/gold/sample) is used to simulate the SPR-based optical fiber sensor. Several parameters including the thickness of gold layer, numerical aperture (NA) of fiber, sensing region length and fiber core diameter have been investigated to evaluate the sensitivity and measurement accuracy of sensor. A detailed explanation for the effect of these parameters on the sensor is presented to give a guideline to optimally design the SPR-based optical fiber sensor.     

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.     

Performances of different metals in optical fibre-based surface plasmon resonance sensor

The capability of various metals used in optical fibre-based surface plasmon resonance (SPR) sensing is studied theoretically. Four metals, gold (Au), silver (Ag), copper (Cu) and aluminium (Al) are considered for the present study. The performance of the optical fibre-based SPR sensor with four different metals is obtained numerically and compared in detail. The performance of optical fibre-based SPR sensor has been analysed in terms of sensitivity, signal-to-noise (SNR) ratio and quality parameter. It is found that the performance of optical fibre-based SPR sensor with Au metal is better than that of the other three metals. The sensitivity of the optical fibre-based SPR sensor with 50 nm thick and 10 mm long Au metal film of exposed sensing region is 2.373 μm/RIU with good linearity, SNR is 0.724 and quality parameter is 48.281 RIU^− 1. The thickness of the metal film and the length of the exposed sensing region of the optical fibre-based SPR sensor for each metal are also optimized.     

Improvement of plasmonic field-matter interaction by subwavelength dielectric gratings

We experimentally and theoretically investigate that detection sensitivity in surface plasmon resonance (SPR) biosensors can be significantly enhanced by employing subwavelength dielectric gratings deposited on a gold film. The enhancement originates from an improvement of field-matter interaction: enhanced evanescent field intensity at the binding region and increased surface reaction area. Using a large-area SiO₂ grating array fabricated by nanoimprint lithography, experimental sensor performance measured by parylene film coating shows that the SPR substrates combined with a dielectric grating provide a notable sensitivity improvement compared to a conventional bare gold film. We also demonstrate that plasmon field can be more confined and enhanced at the dielectric gratings with a larger width. The proposed SPR structure could potentially be useful in a variety of plasmonic applications including high-sensitivity biosensors.     

Bimetallic Silver–Gold Film Waveguide Surface Plasmon Resonance Sensor

Abstract

It is desirable that a surface plasmon resonance (SPR) sensor is highly sensitive to binding interactions within the sensing region, generate evanescent fields with long penetration depths, and utilize a metal film that is very stable even in extreme environmental conditions. In this study, we present the first example of a wavelength-modulated waveguide SPR sensor with a bimetallic silver–gold film for surface plasmon excitation. The underlying silver yields better evanescent field enhancement of the sensing surface, while the overlying gold ensures that the stability of the metallic film is not compromised. It is shown experimentally that in terms of dλ/dn, the bimetallic film waveguide SPR configuration has a sensitivity of 1232 nm/RIU, greater than two times improvement from the 594 nm/RIU achievable with single gold film waveguide SPR sensor. The higher sensitivity, compact nature, and better evanescent field enhancement of this configuration provides the potential to biosensing applications.     

Bimetallic Silver-Gold Film Waveguide Surface Plasmon Resonance Sensor

It is desirable that a surface plasmon resonance (SPR) sensor is highly sensitive to binding interactions within the sensing region, generate evanescent fields with long penetration depths, and utilize a metal film that is very stable even in extreme environmental conditions. In this study, we present the first example of a wavelength-modulated waveguide SPR sensor with a bimetallic silver-gold film for surface plasmon excitation. The underlying silver yields better evanescent field enhancement of the sensing surface, while the overlying gold ensures that the stability of the metallic film is not compromised. It is shown experimentally that in terms of dλ/dn, the bimetallic film waveguide SPR configuration has a sensitivity of 1232 nm/RIU, greater than two times improvement from the 594 nm/RIU achievable with single gold film waveguide SPR sensor. The higher sensitivity, compact nature, and better evanescent field enhancement of this configuration provides the potential to biosensing applications.     

Fiber optic sensor based on surface plasmon resonance with nanoparticle films

This paper reports on a novel design of a fiber optic surface plasmon resonance (SPR) sensor based on nanoparticle metal film. The performance of the proposed sensor in terms of its signal-to-noise ratio (SNR) and sensitivity under different conditions related to the film with spherical gold nanoparticles embedded in a host material is theoretically analyzed. In particular, the effect of the parameters such as gold particle size, film thickness, and refractive index of host material is studied and the possible explanation, whenever required, is given. The numerical results presented in this paper leads to fulfill the requirement of significant optimization of the important design parameters to achieve a high SNR and sensitivity of a fiber optic SPR sensor with nanoparticle films.     

Investigation of the performance of an SPR-based optical fiber sensor using finite-difference time domain

Finite-difference time domain (FDTD) method was used to investigate the performance of surface plasmon resonance (SPR)-based optical fiber sensors. The results show that the performance of the fiber sensor can be optimized by choosing a proper combination of metal layer thickness of 40–60 nm and residual cladding thickness of 400–500 nm. Furthermore, the roughness effect of the gold surface layering the fiber sensor is significant in rough surfaces when sigma rms is greater than 5 nm or correlation length is lower than 100 nm.     

Phase-shift interferometry combined with surface plasmon resonance effect for two-dimensional bio-surface analysis

The phase-shift interferometry combined with surface plasmon resonance (SPR) effect has been studied as a novel technique used to analyze the bio-surface, which measures the spatial phase variation of SPR reflected light. The spatial sensitivity of the SPR imaging sensor is improved over the conventional SPR imaging systems based on optical intensity.     

纳米金表面修饰与表面等离子体共振传感器的相互作用研究

为了分析纳米金表面修饰对表面等离子体共振(SPR)的放大作用,以及其对传感器本身的影响,首先,基于色散介质的吸收理论,通过建立波长型SPR生物传感器四层膜结构的数学模型,理论分析了传感器表面所吸附纳米金对传感器的影响:纳米金的表面修饰,改变了表面等离子体传感器中棱镜表面各介质层内电磁场的能量分布,削弱了金属膜在共振吸收中的作用,从而使SPR曲线的半波宽度增加,最小反射系数增大,金膜的最优膜厚度也随之改变.其次,通过不同厚度的金膜外吸附纳米金的对比试验,验证了此理论.金膜厚45nm、表面修饰10nm纳米金颗 关键词： 表面等离子体共振 生物传感器 纳米金 金属膜     

High-Sensitivity Sensor Based on Surface Plasmon Resonance Enhanced Lateral Optical Beam Displacements

We present a new optical sensor based on surface plasmon resonance （SPIt） enhanced lateral optical beam displacements. Compared with the traditional SPIt methods, the new method provides higher sensitivity to the sensor system. Theoretical simulations show that the refractive index （RI） detection sensitivity of the SPR sensor based on the displacement measurement has a strong dependence on the thickness of the metal film. When the optimal thickness of the metal film is selected, the RI resolutlon of the SPIt sensor is predicted to be 2.2 × 10^-7 refractive index units （RIU）. Furthermore, it is found that the incidence angle can be used as a parameter to adjust the operating range of the sensor to different refractive index ranges.     

偏振控制光强调制型点阵SPR传感器研究

介绍了一种偏振控制光强调制型点阵表面等离子体共振(SPR)传感器,分析了入射角度、金膜厚度、起偏器设置、光源波长及数据处理方式对传感器灵敏度和线性范围的影响,并对632.8 nm与740 nm两种光源传感器系统进行了实验测试与分析.结果表明,偏振控制光强调制型点阵SPR传感器可将光经过表面等离子体共振所产生的偏振态变化...     

用扫描近场光学显微镜技术研究金膜表面等离体子共振

表面等离体子波(SPW)可与入射光横磁波极化能量耦合并被共振激发,这种现象被称为表面等离体子共振现象(SPR)。主要利用扫描近场光学显微镜(SNOM)技术和表面等离体子共振现象技术相结合,来研究金膜表面等离体子共振。设计并建立了结构独特的新型Kretschmann型表面等离体子共振现象耦合装置,同时又设计了具有厚度梯度的表面等离体子的制备方法。在此基础上,测量了改变入射角条件下的表面等离体子共振曲线,测得该装置的等离体子共振角灵敏度为1°。并且对金膜表面进行表面等离体子共振条件下的扫描近场光学显微成像。实验结果表明,在共振时金膜表面的扫描成像比不共振时清晰,而且增加了很多细节。应用表面等离体子共振现象技术将可以明显提高扫描近场光学显微镜的信噪比、分辨力等性能。     

Refractive index sensor based on high-order surface plasmon resonance in gold nanofilm coated photonic crystal fiber

We propose a novel kind of wide-range refractive index optical sensor based on photonic crystal fiber(PCF) covered with nano-ring gold film.The refractive index sensing performance of the PCF sensor is analyzed and simulated by the finite element method(FEM).The refractive index liquid is infiltrated into the cladding air hole of the PCF.By comparing the sensing performance of two kinds of photonic crystal fiber structures, a wide range and high sensitivity structure is optimized.The surface plasmon resonance(SPR) excitation material is chose as gold, and large gold nanorings are embedded around the first cladding air hole of the PCF.The higher order surface plasmon modes are generated in this designed optical fiber structure.The resonance coupling between the fundamental mode and the 5 th order surface plasmon polariton(SPP)modes is excited when the phase matching condition is matched.Therefore, the 3 rd loss peaks appear obvious red-shift with the increase of the analyte refractive index, which shows a remarkable polynomial fitting law.The fitnesses of two structures are 0.99 and 0.98, respectively.When the range of refractive indices is from 1.40 to 1.43, the two kinds of sensors have high linear sensitivities of 1604 nm/RIU and 3978 nm/RIU, respectively.     

Magnetized SPR sensor for enhanced functionality

It is known that a magnetic field changes the RI and the SPR angle of specific analytes. We have applied an external magnetic field to a surface plasmon resonance (SPR) sensor to exploit this phenomenon. A gold film is used for excitation of SPR in the sensor with a Kretschmann configuration. According to the concentration of 4-type analyte, we observed unique changes of the SPR angle due to the magnetic field, providing better classification of material type than a conventional SPR sensor.     

基于空气孔微结构光纤的表面等离子体共振折射率传感器北大核心CSCD

提出了一种基于表面等离子体共振(SPR)效应增强的光子晶体光纤折射率传感器。该传感器结构通过光纤熔接机拼接光子晶体光纤(PCF),在光子晶体光纤中间引入一个空气孔形成PCF-空气孔-PCF的光纤传感结构,随后使用磁控溅射镀膜工艺在其表面沉积一层薄金膜制备而成。实验探究了折射率及温度对传感器的响应。结果表明,在1.333~1.389的折射率范围内,所提出的传感器的平均折射率灵敏度为2 142.52 nm,且测量线性度为0.981,品质因子约13.10。实验结果表明该传感器对温度不敏感。相比于无空气孔的PCF传感结构,引入的空气孔增强了SPR效应,使得传感器拥有良好的共振峰深度。得益于上述优势,该类型传感器有望在生物医学、环境监测等领域得到应用。     

Highly sensitive differential phase-sensitive surface plasmon resonance biosensor based on the Mach-Zehnder configuration

A high-sensitivity surface plasmon resonance (SPR) biosensor based on the Mach-Zehnder interferometer design is presented. The novel feature of the new design is the use of a Wollaston prism through which the phase quantities of the p and s polarizations are interrogated simultaneously. Since SPR affects only the p polarization, the signal due to the s polarization can be used as the reference. Consequently, the differential phase between the two polarizations allows us to eliminate all common-path phase noise while keeping the phase change caused by the SPR effect. Experimental results obtained from glycerin-water mixtures indicate that the sensitivity limit of our scheme is 5.5 x 10(-8) refractive-index units per 0.01 degrees phase change. To our knowledge, this is a significant improvement over previously obtained results when gold was used as the sensor surface. Such an improvement in the sensitivity limit should allow SPR biosensors to become a possible replacement for conventional biosensing techniques based on fluorescence. Monitoring of the bovine serum albumin (BSA) binding reaction with BSA antibodies is also demonstrated.     

契形结构光纤表面等离子体共振传感器研究

提出了一种契形端面结构的光纤表面等离子体共振(SPR)传感器激励模型. 采用时域有限差分法对契形SPR波导的共振模型进行数值模拟, 通过在光纤出射端抛磨契形角度并进行敏感膜修饰, 制出具有契形端面结构的类Kretschmann微棱镜式光纤SPR传感器, 实现激发SPR的光波调制.结果表明, 在1.3330–1.4215折射率范围内, 制备的契形光纤SPR传感器相对于常规光纤SPR传感器, 其平均灵敏度提高了近1–6倍, 1倍和6倍分别出现在小角度结构(15° 契形) 传感器和大角度结构(60°契形) 传感器, 且仍保持 10^-5 等级的分辨率. 该类型结构的传感器具有契形端面激励模式, 设计灵活性高、制备工艺简单、可微量检测样本等优点, 能够很好地适应于不同环境和测量条件的实际生化检测、环境监测需求. 关键词： 光纤传感器 表面等离子体共振 契形端面结构 折射率灵敏度     

Investigation of dual-channel fiber-optic surface plasmon resonance sensing for biological applications

A dual-channel fiber-optic sensor based on surface plasmon resonance (SPR) for self-referencing refractive-index measurements has been proposed. Most applications of fiber-optic SPR sensors are designed to measure the refractive index of a liquid or gas sample by measuring the signal from a single surface, the sensitivity and stability of which is easily affected by the fluctuation of external environmental conditions. We have designed a dual-channel fiber-optic surface sensor with two independent SPR signals from two areas of the same probe. A prototype sensor was fabricated and characterized. The preliminary experimental results demonstrate the characteristic responses of both SPR signals from two channels that independently correspond to the refractive index changes in the liquid samples with which they are in contact. The design could be extended to a multichannel sensor with further developments. The experimental results confirmed that one channel can be used as a reference sensor that could compensate for unexpected changes in bulk refraction or temperature and develop this sensor as a practicable high-sensitivity biosensing device.