Simplification and evaluation of a gold-deposited SPR optical fiber sensor.

The structure of the sensing element of a gold-deposited optical fiber sensor was simplified and quantitative analyses of various alcohols with the sensor showed improvement of the performance. The sensor uses surface plasmon resonance (SPR) at the interface of a sample solution and a thin (10 - 70 nm) gold film deposited on half of the exposed core of the optical fiber. The sensor with a film thickness of 45 nm can detect a small change of 5.6 x 10(-5) refractive index (RI) units in the refractivity. The response time is less than 0.5 min and the relative standard deviation for measurements is less than or equal to 1%. A straight line with a correlation coefficient of 0.9995 was obtained below 10%, v/v in the calibration curve for methanol solutions of benzyl alcohol. The minimum of the response curve due to the maximum excitation of SPR in the refractivity range from 1.33 to 1.44 RI units shifts to a lower refractivity as the film becomes thicker. The response curves of the sensors were calculated from SPR theoretical equations while considering of the distribution in the thickness of the deposited gold films. The improvement in the performance of the sensor is discussed.     

Stability of the gold/silica thin film interface: electrochemical and surface plasmon resonance studies

This article reports chemical stability studies of a gold film electrode coated with thin silicon oxide (SiOx) layers using electrochemical, surface plasmon resonance (SPR) and atomic force microscopy (AFM) techniques. Silica films with different thicknesses (d = 6.4, 9.7, 14.5, and 18.5 nm) were deposited using a plasma-enhanced chemical vapor deposition technique (PECVD). For SiOx films with d >/= 18.5 nm, the electrochemical behavior is characteristic of a highly efficient barrier for a redox probe. SiOx films with thicknesses between 9.5 and 14.5 nm were found to be less efficient barriers for electron transfer. The Au/SiOx interface with 6.4 nm of SiOx, however, showed an enhanced steady-state current compared to that of the other films. The stability of this interface in solutions of different pH was investigated. Whereas a strongly basic solution led to a continuous dissolution of the SiOx interface, acidic treatment produced a more reticulated SiOx film and improved electrochemical behavior. The electrochemical results were corroborated by SPR measurements in real time and AFM studies.     

Preparation and characterization of thin films of SiO(x) on gold substrates for surface plasmon resonance studies

We report here on the fabrication and characterization of stable thin films of amorphous silica (SiO(x)) deposited on glass slides coated with a 5 nm adhesion layer of titanium and 50 nm of gold, using the plasma-enhanced chemical vapor deposition (PECVD) technique. The resulting surfaces were characterized using atomic force microscopy (AFM), ellipsometry, contact angle measurements, and surface plasmon resonance (SPR). AFM analysis indicates that homogeneous films of silica with low roughness were formed on the gold surface. The deposited silica films showed excellent stability in different solvents and in piranha solution. There was no significant variation in the thickness or in the SPR signal after these harsh treatments. The Au/SiO(x) interfaces were investigated for their potential applications as new surface plasmon resonance sensor chips. Silica films with thicknesses up to 40 nm allowed visualization of the surface plasmon effect, while thicker films resulted in the loss of the SPR characteristics. SPR allowed further the determination of the silica thickness and was compared to ellipsometric results. Chemical treatment of the SiO(x) film with piranha solution led to the generation of silanol surface groups that have been coupled with a trichlorosilane.     

Thin chitosan films as a platform for SPR sensing of ferric ions

Homogeneous chitosan films of various thicknesses (10-65 nm) were deposited on thin gold films through spin coating. The resulting interfaces were characterized using surface plasmon resonance (SPR), AFM, profilometry and cyclic voltammetry. The strong chelating properties of chitosan films to Fe(3+) were investigated using cyclic voltammetry. Through SPR measurements, an affinity constant between chitosan and Fe(3+) of 9.49 x 10(5) M(-1) was determined with a detection limit as low as 250 ppb.     

基于金银合金薄膜的高灵敏度宽光谱表面等离子体共振成像传感器

报道了一种基于金银合金薄膜的宽光谱表面等离子体共振成像(SPRI)传感器,该传感器能够对吸附在薄膜局部或整个表面上的生化分子进行原位定量检测,而且与常规的金膜SPRI传感器相比,检测成本更低,检测灵敏度更高。利用质量比1:1的金银合金溅射靶在玻璃基板上淀积了厚约50 nm的均匀的金银合金薄膜。利用实验室自制的Krestchmann结构多功能平台在不同入射角下测试了金银合金薄膜被纯水覆盖后的SPR光谱和SPR彩色图像。基于色相算法计算获得了每个SPR彩像的二维色相分布及其平均色相,从而使得宽光谱SPRI传感器能够利用平均色相作为灵敏度参数进行定量检测。实验确定了平均色相对溶液折射率(RI)变化和分子吸附最为敏感的光谱区间是595–610 nm之间。在这个窄光谱范围内,平均色相与共振波长呈线性关系,其斜率为?hue/?λR=7.52 nm~(-1),这意味着基于色相的RI灵敏度是基于共振波长的RI灵敏度的7.52倍,这一结论已被实验证明。将SPRI传感器的起始共振波长设定在色相敏感光谱区间内之后,实验测得基于色相的RI灵敏度为S=29879 RIU~(-1),比在相同条件下测得的金膜SPRI的灵敏度高8倍。利用时间分辨宽光谱SPRI方法实时监测了牛血清白蛋白(BSA)分子在金银合金薄膜表面的非特异性吸附,从实验测得的平均色相随时间的变化曲线可知BSA吸附达到平衡所需时间约15 min。研究结果表明,基于金银合金薄膜的SPRI传感器具有动态定量检测蛋白质分子吸附过程的功能。     

New Optical Chemical Sensors Based on Surface Piasmon Resonance

A kind of new optical chemical sensors based on surface plasmon resonance (SPR) have been developed recently in this laboratory. Traditionally, the sensors based on SPR are making use of a coupling prism coated with a thin gold film and performed by varying the incidence angle with a goniometer.     

Fiber-optic surface plasmon resonance for vapor phase analyses

Fiber-optic sensors based on surface plasmon resonance (SPR) for direct refractive index (RI) measurements of samples with the RI between 1.00 and 1.30 are described. Most applications of SPR sensors are designed to function near the refractive index of water (1.3330 RI). The RI changes of aqueous solution (RI, ca. 1.34) can easily be monitored by silica-fiber (RI, 1.4601 at 550 nm) based SPR sensor. With regard to gas species detection, the fiber-optic SPR sensor must be modified for sensitivity to changes in refractive index near 1.0008 (i.e., RI of air). However, the silica waveguide has a prohibitively high RI for unmodified monitoring of the RI changes of gas. The silica-fiber based SPR probe design presented here is based upon the modification of the probe geometry to the ability to tune the SPR coupling wavelength/angle pair. In this study, the tapered silica-based fiber SPR sensors are shown to directly determine the RI changes of gas species and the density change of dry air.     

Gold films deposited over regular arrays of polystyrene nanospheres as highly effective SERS substrates from visible to NIR

Gold nanostructured films of various thicknesses (15, 30, and 60 nm) are deposited over regular arrays of polystyrene nanospheres in an attempt to evaluate their potential as SERS-active substrates. Atomic force microscopy is used to topographically characterize the substrates as well as to ensure the thickness of the deposited gold films. The optical response of the prepared substrates recommends their use in SERS experiments with multiple laser lines from visible and NIR spectral domains. The assessment of the substrates' SERS activity is performed by using the 532, 633, and 830 nm excitation lines and different average enhancement factor (EF) values are obtained depending on the film thickness and employed laser line. The 60 nm gold nanostructured film generates the greatest local electromagnetic field confinement under NIR excitation and consequently gives rise to maximum SERS enhancement. The large tunability of surface plasmon excitation combined with the advantage of relatively high exhibited average EF values obtained under NIR excitation recommends these substrates as outstanding candidates for upcoming investigations of biological relevant molecules.     

纳米多孔金薄膜的表面等离子体共振传感特性

对淀积在玻璃衬底上厚度约60 nm的金银合金溅射薄膜进行硝酸腐蚀脱银处理, 得到纳米多孔金薄膜. 利用自建的波长检测型表面等离子体共振(SPR)传感装置研究了腐蚀时间对纳米多孔金薄膜SPR特性的影响, 结果发现纳米多孔金薄膜与水溶液接触后在400-900 nm光谱范围内不具有SPR效应, 而当薄膜置于空气中时会产生明显的传播等离子体共振吸收峰, 其共振波长随腐蚀时间增加逐渐红移. 纳米多孔金薄膜在空气气氛中的SPR效应使其能够用于原位监测气相分子在孔内的吸附, 还可对在液相中吸附的生化分子进行离位测试. 本文对L-谷胱甘肽、L-半胱氨酸、2-氨基乙硫醇三种含巯基的生化小分子在纳米多孔金薄膜内的吸附进行了离位分析, 结果表明与传统的致密金薄膜SPR芯片比较, 纳米多孔金薄膜对这些分子显示出更高的灵敏度和更低的检测下限, 这归功于多孔金的大比表面积使其能够吸附大量的生化小分子. 实验还对乙醇蒸气在纳米多孔金薄膜内的吸附进行了原位监测, 发现吸附平衡所用时间较长, 约为160 min.     

Analytical characterization of thin carbon films

CH(x) films on silicon substrates deposited by a Mesh Hollow Cathode Process (MHC) were analyzed by various techniques. The films were produced with varying deposition times, resulting in thicknesses ranging from ~2-20 nm. X-Ray Reflectivity (XRR) was used to determine the film thicknesses and the deposition rate. A good correlation of measured XRR thicknesses with SIMS sputter depths down to the film-substrate transition was found.An AFM-based nanoscratching technique was applied to test the wear resistance of the thin overcoats. The MHC films reveal slightly decreasing scratch resistance for reduced film thicknesses, which can be explained by a higher fraction of soft interface zones for thinner films.This is in accordance with Raman spectroscopic measurements in the visible spectral range which were carried out to examine the carbon bonding properties. Combined analysis of G peak position and D/G peak intensity ratio indicates a more graphitic structure for film thicknesses less than 10 nm.     

Single-crystal sapphire-fiber optic sensors based on surface plasmon resonance spectroscopy for in situ monitoring

Single-crystal sapphire-fiber optic sensors based on surface plasmon resonance (SPR) for refractive index (RI) measurements of aqueous and hydrothermal water solutions are described. Accurate measurement of RIs is essential to efficient operation and control of broad range of engineering processes. Some of these processes are carried out with harsh environments, such as high-temperature, high pressure, and chemical corrosion. These extreme physical conditions are proving a limiting factor in application of the conventional silica-based optical sensors. Single-crystal sapphire is an ideal material for sensor applications, where reliable performance is required in the extreme environment conditions. With regard to the liquid species detection, most applications of SPR sensors are designed to function near the refractive index of water (1.3330 RI). The RI changes of aqueous solution can be easily monitored by silica-fiber (RI, 1.4601 at 550 nm) based SPR sensor. However, the sapphire waveguide has a prohibitively high RI (1.7708 at 546 nm) for unmodified monitoring of the RI changes of aqueous solutions. For that purpose, a practical SPR probe geometry has been applied to the ability to tune the SPR coupling wavelength/angle pair with sapphire-fiber based SPR probe.     

热诱导金属/聚合物膜系图案化控制的研究

近年来 ,在简单体系上形成复杂规则的图案已引起诸多学者的注意 ,其中以聚合物为母体的体系发展了模板、局部紫外照射和激光诱导等一系列技术 ,从而得到可控的表面图案[1～ 6] .本文用激光刻蚀法对溅射在聚合物膜上的金属薄膜进行处理 ,在热诱导情况下使金属 /聚合物膜系表面产生了规则的图案 .薄膜热应力的可控释放作用和激光刻蚀造成的区域局限作用被认为是诱导这种可控图案产生的两种基本要素 .通过控制激光刻蚀区域 ,可控制薄膜表面形貌变化 ,从而实现可控的图案化设计 .1　实验部分1.1　原料及仪器　聚苯乙烯 (PS) :北京燕山石油化工…     

Spun films of perylene diimide derivative for the detection of organic vapors with host–guest principle

The optical characterization and chemical vapor sensing properties of 1,7-dibromo-N,N′-(bicyclohexyl)-3,4:9,10-perylene diimide thin film against to organic vapors were discussed in this study by using spin coating, UV–Vis spectroscopy, atomic force microscopy, surface plasmon resonance (SPR) and Quartz Crystal Microbalance (QCM) techniques. The perylene diimide thin films were fabricated with a refractive index values from 1.55 to 1.60 and thicknesses in the range between 15.80 and 26.32 nm using different spin speeds from 1000 to 5000 rpm. In this study, perylene diimide thin film sensor was exposed to dichloromethane, chloroform, carbon tetrachloride, tetrahydrofuran and ethyl acetate vapors by using both SPR and QCM techniques. Also, the swelling behaviors of the perylene diimide thin films prepared at different spin speeds were investigated with respect to dichloromethane vapor at the room temperature by using SPR data. Diffusion coefficients were found to be 11.34?×?10^?17 (1000 rpm), 2.56?×?10^?17 (3000 rpm) and 0.38?×?10^?17 cm² s^?1 (5000 rpm) for dichloromethane vapor by using the Fick’s law of diffusion. It might be proposed that perylene diimide thin film optical chemical sensor element has a good sensitivity and selectivity for the dichloromethane vapor at room temperature.     

Structural and optical characterization of thermally evaporated cadmium sulfide thin films

The article reports the structural and optical properties of vacuum‐evaporated cadmium sulfide (CdS) films with different thicknesses at room temperature. The structural investigations performed by means of X‐ray diffraction (XRD) technique have showed that all the films have the zinc‐blende structure, a face‐centered cubic form with lattice constants a = b = c = 5.82 Å and point group F4 3m. Crystallite sizes calculated from Scherrer relation are in the range of 173–345 Å. So far, because the optical parameters of the metastable cubic CdS have not been so well known, we apply spectroscopic ellipsometry to determine the thickness, optical constants and energy band gap of CdS thin film deposited by thermal evaporation onto opaque gold substrate, a perfect reflectivity and inert metal. As shown the measured spectral behavior of the optical constants and the band gap value of CdS thin film are in agreement with those obtained by the reflectance and transmittance methods. The energy band gap of CdS thin film determined from the spectral behavior of the absorption coefficient is about 2.46 eV. Copyright © 2008 John Wiley & Sons, Ltd.     

Surface plasmon resonance as a time-resolved probe of structural changes in molecular films: considerations for correlating resonance shifts with adsorbate layer parameters

Surface plasmon resonance (SPR) spectroscopy is an efficient probe of transient structural changes in molecular films. To analyze kinetic SPR data for such systems, generally it is necessary to adapt an adequate theoretical framework that would allow one to express the measured optical quantities (time-dependent shifts of the resonance angle or wavelength) in terms of the structural parameters (layer thickness, mass density, or surface coverage) of the sample molecules. We present here theoretical calculations and illustrative experimental results to address certain essential elements of this type of data analysis for transient SPR systems. The phenomenological framework we consider here is based on multilayer reflectivity calculations, and can be applied to a broad class of systems involving ordered molecular layers on supporting gold films. A typical application of these calculations is demonstrated through the analysis of specific SPR experiments designed to probe the kinetics of pH-induced structural changes in a molecular film of 11-mercaptoundecanoic acid (MUA) on a thin gold film.     

Au nanoparticles prepared by physical method on Si and sapphire substrates for biosensor applications

Gold nanoparticles heavily functionalized with oligonucleotides have been used in a variety of DNA detection methods. The optical properties of three-dimensional aggregates of Au nanoparticles in solution or deposited onto suitable surfaces have been analyzed to detect hybridization processes of specific DNA sequences as possible alternatives to fluorescent labeling methods. This paper reports on the preparation of gold nanoparticles directly deposited onto the surface of silicon (Si) and sapphire (Al2O3) substrates by a physical methodology, consisting in the thermal evaporation of a thin Au film and its successive annealing. The method guarantees the preparation of monodispersed single-crystal Au nanoparticles with a strong surface plasmon resonance (SPR) peak centered at about 540 nm. We show that the changes of SPR excitation before and after DNA functionalization and subsequent hybridization of Au nanoparticles immobilized onto Si and Al2O3 substrates can be exploited to fabricate specific biosensors devices in solid phase.     

Nano ZnO thin films synthesis by sol–gel spin coating method as a transparent layer for solar cell applications

Zinc oxide nano-structured thin films have been synthesized by low-temperature and cost-effective sol–gel spin coating method. Zinc oxide films with good adherence have been deposited on soda lime glass substrates with two thicknesses 250.15 and 311.32?nm. High transmission (>95%) zinc oxide films with proper interference fringes in the visible and near infrared region have been obtained. Film thickness, optical constants and dispersion parameters have been calculated accurately by using Swanepoel method, which basely depends on the interference fringes of the transmission spectra. Zinc oxide films have direct optical band gap, its values slightly change with the annealing temperatures and film thickness. The X-ray diffraction studies indicated the hexagonal wurtzite structure for zinc oxide films with preferred orientation along (002) plane. Raman spectroscopy confirmed the hexagonal structure for the films. The average particle size is in the nano-scale and the crystallinity level increases with the annealing temperatures and film thickness.

     

Electrospray ionization from a droplet deposited on a surface-modified glass rod

This paper reports development of a non-mechanical electrospray ionization (ESI) method to generate electrospray from a droplet deposited on an optical fiber coated with a thin gold or Nafion film. Modification of the surface of the optical fiber in this manner increases its wettability, such that a droplet of the aqueous sample solution can adhere sufficiently strongly to the tip of the fiber. The aqueous sample solution was deposited near the tip of the fiber with a micropipette. When a high voltage (2,000 V) was applied to the fiber by electrical connection through the gold film, the sample solution moved and hung at the tip of the fiber. Simultaneously, ESI was generated from the sample droplet. Multiply charged peptide and protein ions were detected by connecting the ESI source to a quadrupole mass analyzer.     

The microstructure and properties of thin WO3 films modified by gold

Direct current magnetron sputtering of a metallic W + Au target or high-frequency magnetron sputtering of WO₃ + Au oxide targets was used to prepare thin (about 100 nm) nanocrystalline WO₃ films with the addition of gold (disperse layers of catalytic gold were additionally deposited on the surface of films). The composition and micromorphology of the surface of films and the electrical and gas sensitive characteristics of nitrogen dioxide sensors were studied to determine the mechanism of the influence of gold on the properties of WO₃ films. The films were shown to contain the β-WO₃ orthorhombic and γ-WO_2.72 monoclinic phases and gold particles. The presence of the nonstoichiometric γ-WO_2.72 phase was shown to increase the concentration of oxygen vacancies in films and decrease the resistance of sensors to 1–2 MΩ. Gold nanoparticles 9–15 nm in size segregated on the surface of semiconductor crystallites and increased the response of sensors to NO₂. The conclusion was drawn that deposited catalytic gold layers increased the response to traces of nitrogen dioxide.     

Electrochemical Surface Plasmon Resonance Spectroscopy at Bilayered Silver/Gold Films

Bilayered silver/gold films (gold deposited on top of the silver film) were used as substrates for electrochemical surface plasmon resonance spectroscopy (EC-SPR). EC-SPR responses of electrochemical deposition/stripping of copper and redox-induced conformation changes of cytochrome c immobilized onto self-assembled monolayers preformed at these substrates were measured. Influence of the Ag layer thickness and the double-layer capacitance on the EC-SPR behavior was investigated. The results demonstrated that the bilayered Ag/Au metal films produce a sharper SPR dip profile than pure Au films and retain the high chemical stability of Au films. Contrary to the result by the Fresnel calculation that predicts a greater fraction of Ag in the bilayered film should result in a greater signal-to-noise ratio, the EC-SPR sensitivity is dependent on both the Ag/Au thickness ratio and the chemical modification of the surface. Factors affecting the overall SPR sensitivity at the bilayered films, such as the film morphology, potential-induced excess surface charges, and the adsorbate layer were investigated. Forming a compact adsorbate layer at the bilayered film diminishes the effect of potential-induce excess surface charges on the SPR signal and improves the overall EC-SPR sensitivity. For the case of redox-induced conformation changes of cytochrome c, the SPR signal obtained at the bilayered silver/gold film is 2.7 times as high as that at a pure gold film.