Numerical investigation for SPR-based optical fiber sensor

In the present work, a theoretical analysis of a surface plasmon resonance (SPR)-based optical fiber sensor is carried out. For the SPR-based optical fiber sensor with four-layer mode (fiber core/metal/sensing layer/sample), the effect of the thickness of metal layer and sensing layer on the spectrum of the transmitted power and wavelength has been studied. Based on the propagation wavevector till the first order expansion of the dispersion function, a detailed explanation for the relationships between the resonance wavelength with the thickness of the metal layer and sensing layer is presented.     

Fiber-optic chemical and biochemical probes based on localized surface plasmon resonance

A novel reflection-based localized surface plasmon resonance fiber-optic probe for chemical and biochemical sensing is reported. The sensor is based on intensity measurement of the internal reflected light at a fixed wavelength from an optical fiber where the extinction cross-section of self-assembled gold nanoparticles on the unclad portion of the optical fiber changes with different refractive index of the environment near the gold surface. The reflection-based localized surface plasmon resonance fiber-optic probe has been shown to be capable of direct sensing of the “spectroscopically silent” Ni²⁺ ion and label-free detection of streptavidin and staphylococcal enterotoxin B at the picomolar level.     

Optical parameters of calix[4]arene films and their response to volatile organic vapors

The Langmuir-Blodgett (LB) technique was employed to produce thin LB films using an amphiphilic calix-4-resorcinarene onto different substrates such as quartz, gold coated glass and quartz crystals. The characteristics of the calix LB films are assessed by UV-visible, quartz crystal microbalance (QCM) and surface plasmon resonance (SPR) measurements. UV-vis and QCM measurements indicated that this material deposited very well onto the solid substrates with a transfer ratio of >0.95. Using SPR data, the thickness and refractive index of this LB film are determined to be 1.14 nm/deposited layer and 1.6 respectively. The sensing application of calixarene LB films towards volatile organic vapors such as chloroform, benzene, toluene and ethanol vapors is studied by the SPR technique. The response of this LB film to saturated chloroform vapor is much larger than for the other vapors. The response is fast and fully recoverable. It can be proposed that this sensing material deposited onto gold coated glass substrates has a good sensitivity and selectivity for chloroform vapor. This material may also find potential applications in the development of room temperature organic vapor sensing devices.     

Cholesteric liquid crystals for detection of organic vapours

Studies on the use of cholesteric liquid crystals (CLCs) as sensing phase for detection of organic vapours in air are described. Stock solutions of 1.0% (w/v) cholesteryl nonanoate (CN) and cholesteryl chloride (CC) were prepared in tetrahydrofuran. Binary mixtures, with compositions ranging from 0.18 to 0.25% of CC and 0.82–0.75% of CN, respectively, were prepared by appropriate mixing of the stock solutions. Films were cast by pipetting three 10 μl aliquots of the CLC solution mixture onto a glass disk, whose reverse side was made black to absorb unscattered light. The glass disk was adapted to the common end of a bifurcated optical fibre bundle and placed in a glass vial, which provided a headspace of organic vapours. Measurements were carried out at 27±1 °C, a temperature in which the CLC mixtures maintain their liquid crystalline properties. The responses of the CLC mixtures to vapours of ethanol, acetone, benzene, pyridine and hexane were investigated. The colour of the sensing phases depended on their compositions and exposure to organic vapours gives rise to a change in the optical characteristics of liquid crystals. It was found that the CLC layers containing 0.23–0.25% of CC had no significant change in optical properties when exposed to organic vapours and that ethanol did not cause any optical changes in the liquid crystal layers. Benzene as well as hexane always turned all the coloured liquid crystalline layers to colourless. The CLC layers exhibited different behaviours to vapours of acetone and pyridine. For example, the wavelengths of maximum scattering for the 0.19% CC layer were 530 nm in air, 545 nm in pyridine and 580 nm in acetone. The CLC layers showed reversibility. The lifetimes of these layers (interval of time in which the liquid crystalline phase exists, before crystallisation) were investigated by employing acetone and n-hexane vapours. Average lifetimes of 14–15 min were found for films in contact with these vapours, while a lifetime of 205 min was possible when the CLC film was exposed to air.     

Interaction of thin films of hydroxo-oxobis(8-quinolyloxo) vanadium (V) with ammonia vapour

Hydroxo-oxobis(8-quinolyloxo) vanadium (V) organometallic complex has been prepared as thin films from dichloromethane solution by spin coating and the kinetics of its interaction with ammonia vapour is investigated using surface plasmon resonance (SPR) technique. Thin film parameters are deduced from SPR measurements as well as spectroscopic ellipsometry and UV–vis spectral absorption measurements. Initial exposure to ammonia vapour has resulted in a permanent change to the baseline of the measured kinetic response, which is explained by the formation of the ammonium salt of the complex. Further exposures to ammonia vapour after 24 h and beyond, are shown to be highly reversible, which can be ascribed to formation of hydrogen bonding of second ammonia molecule with the highly negatively charged ammonium salt of the vanadium complex. Exposures to other organic vapours such as ethanol, chloroform and benzene are also studied in order to examine the selectivity of this material to ammonia vapour.     

光纤表面等离子体波传感器中共振波长的理论计算

光纤SPR传感器是一种新型传感器,可在多个领域实现远距离实时在线监测.根据表面等离子体波的共振条件计算了光纤SPR传感器的关键参数--共振波长,并且给出在一定条件下传感器的最大量程.为光纤SPR传感器的设计提供了有力的工具.     

Identification and quantification of different vapours using a single polymer chemoresistor and the novel dual transient temperature modulation technique

This paper presents a novel signal processing technique for a square wave temperature modulated carbon black/polymer composite sensor. The technique consists of only two mathematical operations: summing the off- and on-transients of the conductance signals, and subtracting the steady-state conductance signal. The technique has been verified through its application to a carbon black/polyvinylpyrrolidone composite chemoresistor. Identification of water, methanol and ethanol vapours was successfully demonstrated using the peak time of the resultant curves. Furthermore, quantification of those vapours was found to be possible using the height of the peak heights, which was linearly proportional to concentration. The technique does not require zero-gas calibration and thus is superior to previously reported techniques.     

An optical sensor for nitrogen dioxide based on a copper phthalocyanine Langmuir—Blodgett film

A copper phthalocyanine Langmuir—Blodgett film has been incorporated in an optical gas sensor which exploits the phenomenon of surface plasmon resonance. For the detection of nitrogen dioxide, a significant improvement over previous work is demonstrated. The use of an ultra-thin layer of nickel to protect the underlying silver layer is also reported.     

A method for determining the mutual diffusion coefficient of molecular solutes based on surface plasmon resonance sensing

An experimental method, combining surface plasmon resonance sensing and microfluidics, to determine the mutual diffusion coefficient of molecular solutes, as ethanol and bovine serum albumin, is presented. Representative refractive index variations of analyte samples over time, and associated dynamic solute concentration profiles, respectively, have been employed to access molecular transport parameters. From both, Fick’s diffusion length and Taylor’s pulse dispersion methods, solute and solvent mutual diffusion coefficients for diluted ethanol and concentrated protein aqueous solutions have been obtained. Additionally, the dynamic behavior and geometry effects of molecular transport have been exploited using finite element simulations for the 3-dimensional case and confirmed experimentally. The numerical simulation also addresses the influence of temperature effects.     

Vapour sensing with conductive polymer nanocomposites (CPC): Polycarbonate-carbon nanotubes transducers with hierarchical structure processed by spray layer by layer

The development of conductive polymer nanocomposite (CPC) sensors for volatile organic compounds (VOC) detection has been carried out using a spray layer by layer (LbL) process. This technique was successfully used to hierarchically structure polycarbonate-multiwall carbon nanotubes (PC-CNT) solutions into a double percolated architecture as attested by atomic force microscopy (AFM) and optical microscopy (OM). PC-CNT vapour sensing behaviour was investigated as a function of CNT content, films thickness, vapour flow and vapours solubility parameter. The response ranking A_r(toluene) > A_r(methanol) > A_r(water) of PC-CNT was found to be coherent with κ₁₂ Flory–Huggins interaction parameters provided that signals are normalised by analyte molecules number. Signals shape was interpreted to the light of Langmuir–Henry–Clustering (LHC) model and found to be proportional to vapour content.     

光纤表面等离子体共振传感检测系统的数据处理

给出了光纤SPR传感检测系统的输出信号处理模型,采用Shpiro-Wilk检验确认了测试噪声的高斯特性;在保证精度的前提下降低了数据采集量;用线性拟合方法处理数据、获得共振波长并测算出最小运算长度,从而把工作量降至原有的4%,使检测更为高效便捷.     

High-sensitive SPR sensing with Indium Nitride as a dielectric overlay of optical fibers

In this work, an Indium Nitride (InN) dielectric overlay has been used to develop a surface plasmon resonance optical fiber sensor. Although InN is a very promising material in electronics industry, this is the first time that this kind of material is used for optical sensing. The obtained results show an improvement of the reliability and long term stability with respect to previous devices made with the same technology. More remarkably, the sensitivity increases up to 11,800 nm/RIU in the range of outer refractive indices between 1.415 and 1.429, the highest sensitivity achieved with this kind of devices. Therefore, a novel application of the InN to optical fiber sensors is demonstrated. The use of this material would be of great interest to produce new SPR-based devices for chemical and biological sensing.     

Absorption-based fiber optic surface plasmon resonance sensor: a theoretical evaluation

In this paper, an optical absorption based fiber optic surface plasmon resonance (SPR) sensor has been studied theoretically. The theoretical treatment is based on Kretschmann’s SPR theory and the Lorentz model that expresses a damped harmonic oscillator is included in the treatment for optical absorption in the sensing layer. The optical source considered is an un-polarized collimated beam. The light is coupled to the fiber using a microscope objective that focuses the beam at the center of the input face of the fiber. The effects of the parameters related to the sensing region, the light source and the optical fiber on the sensitivity and the operating range of the SPR sensor have been studied with the help of numerical calculations and computer simulations. It has been found that the excitation frequency in absorption-based fiber optic SPR sensor is an important parameter. The sensitivity is better for the lower off-resonance excitation frequency. The sensitivity and the operating range of the sensor are better for large value of the core diameter. The optimization of numerical aperture of the fiber, film thickness and the length of the sensing region is required to achieve the maximum sensitivity. Further, the increase in the extinction coefficient of the sample increases the sensitivity of the sensor while the decrease in the width of its absorption spectrum increases the sensitivity. The sensitivity and the operating range of the sensor are better for small values of the refractive index of the absorbing sample.     

Binary monolayers of single-stranded oligonucleotides and blocking agent for hybridisation

The hybridisation of thiol-modified single-stranded DNA (SH-ssDNA) embedded in lipoate or hydrophilic polymer monolayers on gold have been studied through the technique of surface plasmon resonance (SPR). SH-ssDNA and the blocking agents were co-adsorbed on gold from the same solution or the surface was post-treated with the blocking agents. The assembling process is allowed to take place for only 10 min. Binding of non-complementary and complementary DNA is dependent both on the blocking agent and on the assembling method used. The lowest non-complementary binding and the highest complementary binding of DNA was obtained with a layer assembled from a binary solution of SH-ssDNA and the lipoate blocking agent.     

Novel e-nose for the discrimination of volatile organic biomarkers with an array of carbon nanotubes (CNT) conductive polymer nanocomposites (CPC) sensors

We report the original design of a new type of electronic nose (e-nose) consisting of only five sensors made of hierarchically structured conductive polymer nanocomposites (CPC). Each sensor benefits from both the exceptional electrical properties of carbon nanotubes (CNT) used to build the conductive architecture and the spray layer by layer (sLbL) assembly technique, which provides the transducers with a highly specific 3D surface structure. Excellent sensitivity and selectivity were obtained by optimizing the amount of CNT with five different polymer matrices: poly(caprolactone) (PCL), poly(lactic acid) (PLA), poly(carbonate) (PC), poly(methyl methacrylate) (PMMA) and a biobased polyester (BPR). The ability of the resulting e-nose to detect nine organic solvent vapours (isopropanol, tetrahydrofuran, dichloromethane, n-heptane, cyclohexane, methanol, ethanol, water and toluene), as well as biomarkers for lung cancer detection in breath analysis, has been demonstrated. Principal component analysis (PCA) proved to be an excellent pattern recognition tool to separate vapour clusters.     

Manufacture of robust surface plasmon resonance fiber optic based dip-probes

Surface plasmon resonance (SPR) spectroscopy has been conducted on both prism and fiber optic (FO) based sensors for several years. This technique measures the refractive index (RI) of a solution or layer adsorbed to a thin (50 nm) Au layer on the sensor substrate. To date a succinct set of protocols have not been published regarding the optimization of fiber-based SPR dip-probe sensors. Such sensors would allow application of SPR to a wider variety of applications. This paper focuses on consideration of the choice of fiber, isolation of the mirror from the sensing area, and orientation of the probes in the metal layer sputter deposition chamber in the manufacture of SPR dip-probes for reproducibility and robustness. Optimization of the process yields sensors with a batch to batch reproducibility as low as 0.5 nm in the location of the SPR spectral minima. Further study of RI measurements by the same probe over 2 months show these SPR dip-probes have a long shelf-life. A selection of probes was exposed to various solutions to monitor their drift. The data shows the probes’ response indicated a lowering of the RI measured over a period of 3 or 7 days depending on the probe type. Evidence of surface porosity and damage upon exposure to hydrothermal water seems to indicate these sensors are prone to chemical attack. Further research is needed to characterize this attack and allow creation of more robust sensors.     

Surface plasmon resonance based fiber optic sensor for the detection of low water content in ethanol

A fiber optic sensor utilizing surface plasmon resonance (SPR) has been fabricated for the detection of low content of water in ethanol. The sensor utilizes spectral interrogation technique for operation. The resonance wavelength has been found to vary linearly with water content in the range 0-10% with sensitivity of 1.149 nm per percentage of water. The results are in agreement with the refractive index variation of ethanol-water mixture. The sensor has a water resolution of 0.145% which is better than the evanescent wave absorption sensor reported for the similar study. The sensor will find application in determining the low water content in ethanol which is used as a bio-fuel and in the field of medicine and organic chemistry.     

Surface plasmon resonance in chalcogenide glass-based optical system

The surface plasmon resonance phenomenon has been studied in a chalcogenide glass-based optical system. IR transmission properties of these materials combined to their high refractive indices lead to advantageous properties for sensing. In this study, numerical simulations have been carried out to investigate the potentialities of sulfide glass from the GeGaSbS system as a coupling prism material. Then, an angular modulation SPR biosensor has been set up in the Kretschmann–Raether arrangement. Experimental data are consistent with numerical calculation and the detection limit of the sensor is 3 × 10⁻⁵ RIU. These preliminary results are promising. Further investigations have to be carried out to confirm the great potentialities of those materials for SPR-based biosensor.     

表面等离子共振传感器的研究进展

表面等离子体是在金属和电介质交界面上所形成的电荷层,在电磁波的激励下表面等离子体发生共振现象,影响电磁波的传播。根据这一原理制作的表面等离子共振传感器可对化学和生物等量进行探测。介绍了表面等离子共振传感器的工作原理和最新研究进展。由于具有体积小、准确度高、抗电磁干扰能力强和可用于遥测等优点,SPR传感器将有广泛的应用前景。     

Diffractive optical coupling element for surface plasmon resonance sensors

Design, technological features, and performance of polymeric diffractive optical coupling elements (DOCEs), developed for surface plasmon resonance (SPR) sensors are reported. The concept is based on input and output coupling of collimated and perpendicularly incident light beams to exchangeable SPR sensor chips. In the SPR sensor chips, one DOCE couples the input light beam to a (bio-)chemical sensor surface and another DOCE images the output light beam onto a detector array. The manufacturing technique is based on an injection moulding process similarly to the manufacturing process of compact discs allowing precision manufacturing and reproduction of the grating topography of the DOCEs. The DOCE-based SPR sensor chip is specifically suitable for miniaturisation and large scale production, while maintaining high optical quality and performance.