表面等离激元共振生物传感分析及应用

基于物理中发生在金属表面的表面等离激元现象 ,阐述表面等离激元共振生物传感分析原理 ;进而建立表面等离激元共振生物传感成像。给出应用表面等离激元共振研究生物单元相互作用的实例。     

基于LabVIEW的表面等离激元共振测量液体折射率

利用LabVIEW编写硬件控制软件,搭建了基于表面等离激元共振原理的光强探测型液体折射率测量实验平台.实验测量纯水和纯酒精的表面等离激元共振的共振角分别与理论计算数据相吻合,证明该系统测量的共振角数值能正确地反映液体折射率的变化.利用该系统测量了不同浓度的酒精-水混合液的折射率.     

金纳米球壳表面等离激元共振波长调谐特性研究

理论研究了金纳米球壳的几何结构参数, 及物理参量对局 域表面等离激元共振波长调谐特性的影响. 结果表明, 随着壳层厚度的增大, 球壳消光共振峰先蓝移后红移, 高阶峰转向时对应的壳层厚度比低阶峰大, 且该厚度与球壳内径的比值随内径尺寸的增大而减小, 随内核材料或外界环境介电常数的增大而增大, 散射共振峰也有类似的移动规律. 利用电子杂化效应和相位延迟效应对该现象进行了理论解释.     

金纳米球壳对的局域表面等离激元共振特性分析

应用有限元方法, 研究金纳米球壳对的几何结构参数及物理参量对其表面等离激元共振的散射及消光光谱的影响, 并根据等离激元杂化理论进行了理论分析. 结果表明, 随着金壳厚度的增加, 金纳米球壳对的散射及消光共振峰先发生蓝移而后红移, 而随着金纳米球壳间隙的减小, 或者随着金纳米球壳的内核尺寸或内核介质折射率的增大, 散射及消光共振峰均发生红移; 随着金壳厚度或内核尺寸减小, 或者随着内核介质折射率增大, 金纳米球壳对的散射与消光共振强度减弱, 而随着金壳间隙的减小, 金纳米球壳对的散射共振强度先增强后减弱, 而消光共振强度逐渐增强, 数值模拟与理论分析一致.     

局域表面等离激元

局域表面等离激元使得贵金属纳米颗粒具有丰富的光学性质,其应用涵盖能源、生物医学、安全、信息、超材料等诸多领域。文章简要介绍局域表面等离激元的基本性质、贵金属纳米结构中的局域表面等离激元共振耦合以及具有局域表面等离激元特性的贵金属纳米结构的一些重要应用。     

石墨烯覆盖铝纳米光栅表面等离激元共振光谱及传感特性

表面等离激元共振技术具有无需标记、灵敏度高、实时检测等优点,已广泛应用于生物医疗、环境监测及食品安全等领域。相对于传统贵金属材料表面等离激元共振传感器而言,铝表面等离激元共振传感器具有价格低廉、共振光谱带宽小等优点,已逐渐成为了该领域的研究热点。针对铝材料存在与生物分子兼容性差、易氧化等缺点,利用石墨烯化学稳定性好、比表面积大、抗氧化能力强、生物兼容性好等独特优势,将其作为与被测分子直接接触的传感层,提出了一种石墨烯覆盖铝纳米光栅的表面等离激元共振传感器。首先,基于多物理场有限元仿真软件建立了该传感器的物理模型,分别分析了石墨烯层数和铝光栅结构参数(占空比、高度、周期)对传感器共振光谱的影响。结果表明,石墨烯与铝光栅的复合有效增强了入射光波与传感器的相互作用,采用单层石墨烯与铝光栅复合时,共振峰具有最窄的光谱带宽。当铝纳米光栅结构Λ=600 nm,H=40 nm,η=70%时,光谱反射率为零。进一步分析了结构优化后的传感器的传感特性。结果表明,单层石墨烯覆盖铝纳米光栅传感器具有最高的品质因数24.5 RIU-1,其灵敏度高达626 nm·RIU-1。该传感器具有探测精度高、分子兼容性好等优点,能为生化分析、环境监测和食品安全等领域提供一个新的绿色传感平台。     

局域表面等离激元

局域表面等离激元使得贵金属纳米颗粒具有丰富的光学性质,其应用涵盖能源、生物医学、安全、信息、超材料等诸多领域。文章简要介绍局域表面等离激元的基本性质、贵金属纳米结构中的局域表面等离激元共振耦合以及具有局域表面等离激元特性的贵金属纳米结构的一些重要应用。     

表面等离激元共振

表面等离激元共振是一种探测金属表面变化的敏感探针，它可以对转移到金（Ａｕ）膜表面的有机单分子层膜进行测量，测量的装置是以衰减全反射为实验基础的。     

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研究了在三开口劈裂金属纳米环中,当入射场偏振方向不同时出现的多极局域表面等离激元共振现象及折射率传感特性。研究表明,当入射场偏振方向分别沿x 轴和y 轴时,在可见光-近红外区域分别激发起两个和三个明显的共振峰。通过改变缺口的张角,能够实现对共振峰位和强度的可控调整。共振峰位处劈裂纳米环的近场分布表明,LHA(左半弧)和DRHA(双右半弧)之间等离激元的杂化耦合是形成上述共振的原因。劈裂纳米环的多极共振非常适合折射率传感应用。当改变周围环境折射率,入射场沿x 轴偏振时,折射率敏感度的最大值可达到1365nm/RIU;入射场沿y 轴偏振时,折射率敏感度最大值可达2229nm/RIU。     

表面等离激元——机理、应用与展望

等离激元光子学(plasmonics)的研究内容是金属纳米结构独特的光学性质及其应用.随着纳米科技的进步,等离激元光子学已经迅速发展成为一门新兴学科,在生物、化学、能源、信息等领域具有重要的应用前景.文章主要介绍表面等离激元(surface plasmons,SPs)的一些基本物理性质,包括局域的表面等离激元(localized surface plas-mon,LSP)和传导的表面等离激元(propagating surface plasmon polariton,SPP),文章还介绍了表面等离激元的几个重要的应用方向,例如生物/化学传感器、表面等离激元激光、光开关器件以及表面等离激元光逻辑运算,等等.     

混合溶液折射率对局域表面等离子体共振的影响

对水-二甲基亚砜二元混合溶液质量分数和温度与折射率的关系进行了理论和实验研究,对几种经典模型的拟合结果进行了比较,给出了适合水-二甲基亚砜混合溶液的经验公式。对水性金溶胶-二甲基亚砜混合溶液质量分数和温度对局域表面等离子体共振峰值波长的影响进行了理论和实验研究,结果表明：水性金溶胶-二甲基亚砜混合溶液质量分数对共振峰值波长的调节有较好的线性关系和较大的调节范围,当温度从20 ℃增大到60 ℃,混合溶液金溶胶的共振峰值波长增加了1367 pm,温度敏感度为34 pm/K,在0%~100%的质量分数范围内,混合溶液金溶胶的共振峰值波长平均产生8.5103 pm的增长。     

混合溶液折射率对局域表面等离子体共振的影响

对水-二甲基亚砜二元混合溶液质量分数和温度与折射率的关系进行了理论和实验研究,对几种经典模型的拟合结果进行了比较,给出了适合水-二甲基亚砜混合溶液的经验公式。对水性金溶胶-二甲基亚砜混合溶液质量分数和温度对局域表面等离子体共振峰值波长的影响进行了理论和实验研究,结果表明:水性金溶胶-二甲基亚砜混合溶液质量分数对共振峰值波长的调节有较好的线性关系和较大的调节范围,当温度从20 ℃增大到60 ℃,混合溶液金溶胶的共振峰值波长增加了1367 pm,温度敏感度为34 pm/K,在0%~100%的质量分数范围内,混合溶液金溶胶的共振峰值波长平均产生8.5103 pm的增长。     

Measurement of refractive index variation of liquids by surface plasmon resonance and wavelength-modulated heterodyne interferometry

In this study an alternative method based on surface plasmon resonance is proposed for in-situ monitoring of variation in the refractive index of a test sample. A wavelength-modulated light source and an unequal-path-length optical configuration heterodyne interferometer are used to detect the phase difference change, which can then be used to estimate the change in the refractive index of a test sample. The experimental results demonstrate a phase stability of 0.02°. The resolution power of the refractive index is 1.5 × 10^− 6 RIU. This method has several advantages over previously used methods such as simple optical setup, easier operation in real time, and low cost.     

Numerical analysis of surface plasmon nanocavities formed inthickness-modulated metal－insulator－metal waveguides

The enhancement characteristics of the local field in the surface plasmon nanocavities are investigated numerically. The cavity is constructed by placing a defect structure in the thickness-modulated metal--insulator--metal waveguide Bragg gratings. The characteristic impedance based transfer matrix method is used to calculate the transmission spectra and the resonant wavelength of the cavities with various geometric parameters. The finite-difference time-domain method is used to obtain the field pattern of the resonant mode and validate the results of the transfer matrix method. The calculation and simulation results reveal the existence of resonant wavelength shift and intensity variation with structural parameters, such as the modulation period of the gratings, the length and the width of the defect structure. Both numerical analysis and theoretical interpretation on these phenomena are given in details.     

Influence of amount of CTAB and ascorbic acid concentration on localized surface plasmon resonance property of gold nanorod

Gold nanorods (AuNRs) are prepared through seeded growth approach. Synthesis parameters of the amount of cetyltrimethylammonium bromide (CTAB), and concentration of ascorbic acid (AA) were studied. We were aiming for an aspect ratio of 3 which could be achieved by a nanorod feature in the range of 45 nm length and 15 nm width. The absorption spectra are observed with an UV–visible NIR spectrophotometer and analysed theoretically. It is known that there are two plasmon resonance peaks for gold nanorod corresponding to transverse surface plasmon resonance (TSPR) and longitudinal surface plasmon resonance (LSPR), respectively. It is found that as the concentration of CTAB increases, the yield of NRs increases. As the concentration of AA increased from 0.05 to 0.2 M, LSP shifts to longer wavelength but upon further increasing the concentration, LSP shifts back to shorter wavelength. A linear relationship between LSPR wavelength and surrounding medium dielectric constant is obtained, which is in good agreement with the theoretical results.     

Study of electrical field distribution of gold-capped nanoparticle for excitation of localized surface plasmon resonance

The specific optical characteristics which can be observed from noble metal nanostructured materials such as nanoparticles and nanoislands have wide variety of applications such as biosensors, solar cells, and optical circuit. Because, these noble metal nanostructures induce the increment of light absorption efficiency by the enhancing effect of electrical field from localized surface plasmon resonance (LSPR) excitation. However, the enhancing effects of electrical field from LSPR using simple structured noble metal nanostructures for several applications are not satisfactory. To realize the more effective light absorption efficiency by the enhancing effect of electrical field, quite different noble metal nanostructures have been desired for applying to several applications using LSPR. In this study, to obtain the more effective enhancing effect of electrical field, conditions for LSPR excitation using a gold-capped nanoparticle layer substrate are computationally analyzed using finite-difference time-domain (FDTD) method. From the previous research, LSPR excitation using such gold-capped nanoparticle layer substrates has a great potential for application to high-sensitive label-free monitoring of biomolecular interactions. For understanding of detailed LSPR excitation mechanism, LSPR excitation conditions were investigated by analyzing the electrical field distribution using simulation software and comparing the results obtained with experimental results. As a result of computational analysis, LSPR excitation was found to depend on the particle alignment, interparticle distance, and excitation wavelength. Furthermore, the LSPR optical characteristics obtained from the simulation analysis were consistent with experimentally approximated LSPR optical characteristics. Using this gold-capped nanoparticle layer substrate, LSPR can be excited easily more than conventional noble metal nanoparticle-based LSPR excitation without noble metal nanoparticle synthesis. Hence, this structure is detectable a small change of refractive index such as biomolecular interactions for biosensing applications.     

Enhanced photon emission by field emission resonances and local surface plasmon in tunneling junction

We investigated the photon emission spectra on Ag (111) surface excited by tunneling electrons using a low temperature scanning tunneling microscope in ultrahigh vacuum. Characteristic plasmon modes were illustrated as a function of the bias voltage. The one electron excitation process was revealed by the linear relationship between the luminescence intensity and the tunneling current. Luminescence enhancement is observed in the tunneling regime for the relatively high bias voltages, as well as at the field emission resonance with bias voltage increased up to 9 V. Presence of a silver (Ag) nanoparticle in the tunneling junction results in an abnormally strong photon emission at the high field emission resonances, which is explained by the further enhancement due to coupling between the localized surface plasmon and the vacuum. The results are of potential value for applications where ultimate enhancement of photon emission is desired.     

Numerical analysis of plasmon polarition refractive index fiber sensors with hollow core and a long period grating

The main principle of this design is based on the efficient energy transfer between the waveguide mode (WM) and the co-directional SPP provided by a properly designed fiber long period grating (LPG). This LPG is imprinted into a waveguide fiber layer of a specially designed hollow core optical fiber. The simulations are based on the finite element method (FEM) algorithm in electromagnetics and coupled mode theory for gratings. Compared to the previous proposed structure using a fiber Bragg grating (FBG), this novel kind of sensor can greatly enhance the refractive index sensitivity, e.g., from 5.93 nm/RIU (with FBG) to 817 nm/RIU (with LPG) at the sensing refractive index of 1.40. The other advantage is that the working conditions can be performed for the well-developed telecom wavelength windows 1500-1600 nm.     

Nanoplasmonic sensing and QCM-D as ultrasensitive complementary techniques for kinetic corrosion studies of aluminum nanoparticles

Corrosion (oxidation) kinetics of Al nanodisks, 262 nm in diameter and 20 nm in height, was measured in degassed Milli-Q water at 23 °C and neutral pH by quartz crystal microbalance with dissipation monitoring (QCM-D) and nanoplasmonic sensing. The former detects the changes of the resonance frequency and the damping of the oscillation of a piezoelectric quartz crystal resonator. The latter detects the changes of the localized surface plasmon resonance (LSPR) in the metallic part of the Al nanoparticle, caused both by the shrinking metallic core and the changes in the dielectric environment as the oxide grows. Highly resolved kinetic data were obtained which show different corrosion stages. The two techniques yield complementary information not obtainable with one technique alone. Two main corrosion mechanisms, namely homogeneous oxide growth and nanoparticle fragmentation and roughening, are distinguished. The time dependence of the corrosion kinetics, determined using QCM-D, is in agreement with weight gain studies of bulk Al found in literature. The nanoplasmonic sensing measurements are compared to analytical model calculations of LSPR shifts which yield an estimate for the increase of oxide thickness during homogeneous oxide growth.