Optimisation of an integrated optical evanescent wave absorbance sensor for the determination of chlorinated hydrocarbons in water

The suitability of an integrated optical chemical sensor for the determination of highly volatile chlorinated hydrocarbons in aqueous solutions has been proven. The analytes are detected by NIR absorption spectrometry in the evanescent field of an integrated optical strip waveguide generated in a BGG31 (Schott, Germany) glass substrate, which is coated with a hydrophobic polymer superstrate as sensing layer. It has been shown that the sensitivity increases when the refractive index of the superstrate is increased from 1.333 up to 1.46. Different UV-cured polysiloxanes with low cross sensitivity to water have been prepared. Due to the good light transmission properties of the IO-sensors prepared by this method, quantitative measurements have been performed with the model system trichloroethene (TCE) in water. A detection limit of 22 ppm has been found and the sensor response times (t₉₀-value) are between five and fourteen minutes for a coating thickness of around 30 m. The sensor response is totally reversible. The analyte desorbes in air within 2 min. The enrichment of trichloroethene in the polysiloxane coating can be described by film diffusion through the aqueous boundary layer as rate determining step.     

Integrated optical NIR-evanescent wave absorbance sensorfor chemical analysis

A new, long-path integrated optical (IO) sensor for the detection of non-polar organic substances is described. The sensing layer deposited on a planar multimode IO structure is built by a suitable silicone polymer with lower refractive index (RI). It acts as a hydrophobic matrix for the reversible enrichment of non-polar organic contaminants from water or air. Light from the near-infrared (NIR) range is coupled into the planar structure and the evanescent wave part of the light field penetrating into the silicone layer interacts with the enriched organic species. As a result, light is absorbed at the characteristic frequencies of the corresponding C-H, N-H or O-H overtone and combination band vibrations of the analytes. To perform evanescent field absorbance (EFA) measurements, the arc-shaped strip waveguide structure of 172 mm interaction length was adapted to a tungsten-halogen lamp and an InGaAs diode array spectrograph over gradient index fibers. Dimethyl-co-methly(phenyl)polysiloxanes with varying degrees of phenylation were prepared and used as sensitive coating materials for the IO structure. Light attenuation in the arc-shaped waveguides is high and typical insertion losses in the range of 14-18 dB were obtained. When the coated sensors were brought in contact with aqueous samples, the light transmission decreases, which is due to the formation of H(2)O micro-emulsions in the silicone superstrates. Nevertheless, after reaching constant light transmissions, absorbance spectra of aqueous trichloroethene samples were successfully collected. For gas measurements, where water cross sensitivity problems are absent, the sensitivity of the IO device for trichloroethene was tested as a function of the RI of the silicone superstrate. The slope of the TCE calibration function increases by a factor of 10 by using a poly(methylphenylsiloxane) layer with a RI of 1.449 instead of poly(dimethylsiloxane) (RI: 1.41). A comparison of the IO-EFA and an earlier developed fiber-optic EFA sensor for trichloroethene measurements in the gas phase showed an increase in sensitivity per unit length of the waveguide by a factor of up to 120.     

Integrated optical NIR-evanescent wave absorbance sensorfor chemical analysis

A new, long-path integrated optical (IO) sensor for the detection of non-polar organic substances is described. The sensing layer deposited on a planar multimode IO structure is built by a suitable silicone polymer with lower refractive index (RI). It acts as a hydrophobic matrix for the reversible enrichment of non-polar organic contaminants from water or air. Light from the near-infrared (NIR) range is coupled into the planar structure and the evanescent wave part of the light field penetrating into the silicone layer interacts with the enriched organic species. As a result, light is absorbed at the characteristic frequencies of the corresponding C-H, N-H or O-H overtone and combination band vibrations of the analytes. To perform evanescent field absorbance (EFA) measurements, the arc-shaped strip waveguide structure of 172 mm interaction length was adapted to a tungsten-halogen lamp and an InGaAs diode array spectrograph over gradient index fibers. Dimethyl-co-methly(phenyl)polysiloxanes with varying degrees of phenylation were prepared and used as sensitive coating materials for the IO structure. Light attenuation in the arc-shaped waveguides is high and typical insertion losses in the range of 14–18 dB were obtained. When the coated sensors were brought in contact with aqueous samples, the light transmission decreases, which is due to the formation of H₂O micro-emulsions in the silicone superstrates. Nevertheless, after reaching constant light transmissions, absorbance spectra of aqueous trichloroethene samples were successfully collected. For gas measurements, where water cross sensitivity problems are absent, the sensitivity of the IO device for trichloroethene was tested as a function of the RI of the silicone superstrate. The slope of the TCE calibration function increases by a factor of 10 by using a poly(methylphenylsiloxane) layer with a RI of 1.449 instead of poly(dimethylsiloxane) (RI: 1.41). A comparison of the IO-EFA and an earlier developed fiber-optic EFA sensor for trichloroethene measurements in the gas phase showed an increase in sensitivity per unit length of the waveguide by a factor of up to 120.     

Planar Integrated Optical Waveguide Sensor for Isopropyl Alcohol in Aqueous Media

An attenuated total reflection (ATR) sensor for water-miscible organic solvents was constructed using a combination of sol-gel processing and integrated optical waveguide (IOW) technologies. The sensor consisted of single-mode, sol-gel based planar waveguide coated with a 40 nm thick, porous sol-gel indicator layer prepared from methyltriethoxysilane and doped with methyl red. The response of the senor to aqueous isopropyl alcohol (IPA) was investigated. Solvation of the indicator dye by IPA causes the absorbance spectrum to undergo a blue shift coupled with an increase in molar absorptivity. IPA was detected by measuring changes in ATR of the guided mode at 488 nm. A response curve extending from 1 to 100% (v/v) IPA in water was constructed for the sensor, from which a detection limit of 0.7% (v/v) IPA/water was estimated. Response and reversal times were typically less than one minute, making this sensor potentially attractive for on-line monitoring applications. The rapid response characteristics are attributable to relatively weak, reversible interactions between the indicator and analyte.     

光波导二氧化氮气敏传感元件的研究

本文用离子交换法制备K+交换玻璃光波导元件,并在其表面固定纳米级敏感层酞菁铜(CuPc)薄膜,利用光波导气体检测系统对NO2气体进行测试.结果表明,该传感元件常温下对NO2等气体有快速、可逆的响应,并具有重现性好,灵敏度高等特点.     

Silica-stabilized gold island films for transmission localized surface plasmon sensing

Ultrathin gold films prepared by evaporation of sub-percolation layers (typically up to 10 nm nominal thickness) onto transparent substrates form arrays of well-defined metal islands. Such films display a characteristic surface plasmon (SP) absorption band, conveniently measured by transmission spectroscopy. The SP band intensity and position are sensitive to the film morphology (island shape and inter-island separation) and the effective dielectric constant of the surrounding medium. The latter has been exploited for chemical and biological sensing in the transmission localized surface plasmon resonance (T-LSPR) mode. A major concern in the development of T-LSPR sensors based on Au island films is instability, manifested as change in the SP absorbance following immersion in organic solvents and aqueous solutions. The latter may present a problem in the use of Au island-based transducers for biological sensing, usually carried out in aqueous media. Here, we describe a facile method for stabilizing Au island films while maintaining a high sensitivity of the SP absorbance to analyte binding. Stabilization is achieved by coating the Au islands with an ultrathin silica layer, ca. 1.5 nm thick, deposited by a sol-gel procedure on an intermediate mercaptosilane monolayer. The silica coating is prepared using a modified literature procedure, where a change in the reaction conditions from room temperature to 90 degrees C shortened the deposition time from days to hours. The system was characterized by UV-vis spectroscopy, ellipsometry, XPS, HRSEM, AFM, and cyclic voltammetry. The ultrathin silica coating stabilizes the optical properties of the Au island films toward immersion in water, phosphate buffer saline (PBS), and various organic solvents, thus providing proper conditions where the optical response is sensitive only to changes in the effective dielectric constant of the immediate environment. The silica layer is thin enough to afford high T-LSPR sensitivity, while the hydroxyl groups on its surface enable chemical modification for binding of receptor molecules. The use of silica-encapsulated Au island films as a stable and effective platform for T-LSPR sensing is demonstrated.     

Design of new integrated optical substrates for immuno-analytical applications

Integrated optical Mach-Zehnder interferometers supply information on changes in refractive index and/or thickness of a film placed as a superstrate on top of one of its surface wave-guides. The internal propagation of light is influenced by the evanescent field reaching into the superstrate. This propagating light interferes with an uninfluenced wave in the second arm after recombination. The result is an intensity modulation depending on the refractive index parameters of the substrate, the waveguide itself and the properties of the superstrate. Taking an antigen layer as the superstrate, its interaction with antibodies changes its thickness by several nanometers. This can be observed by recording the change in intensity of the signal of the interferometer. The sensitivity of such a device depends on particular values of the optical parameters of substrate and waveguide with respect to the given superstrate properties. Computer calculations help to select optimum glass and waveguide fabrication conditions. The numerical results of a variety of assumed conditions have been tested experimentally. The application to the improved detection of triazines is discussed.     

Fabrication of an optical sensor based on the immobilization of Qsal on the plasticized PVC membrane for the determination of copper(II)

A novel optical sensor has been proposed for sensitive determination of Cu(II) ion in aqueous solutions. The copper sensing membrane was prepared by incorporating Qsal (2-(2-hydroxyphenyl)-3H-anthra[2,1-d]imidazole-6,11-dione) as ionophore in the plasticized PVC membrane containing tributyl phosphate (TBP) as plasticizer. The membrane responds to Cu(II) ion by changing color reversibly from yellow to dark red in acetate buffer solution at pH 4.0. The proposed sensor displays a linear range of 6.3 × 10^?7?1.00 × 10^?4 M with a limit of detection of 3.3 × 10^?7 M. The response time of the optical sensor was about 3?C5 min, depending on the concentration of Cu(II) ions. The selectivity of the optical sensor to Cu(II) ions in acetate buffer is good. The sensor can readily be regenerated by hydrochloric acid (0.1 M). The optical sensor is fully reversible. The proposed optical sensor was applied to the determination of Cu(II) in environmental water samples.     

Characterization of Optical Fiber Dissolved Oxygen Sensor for Aquaculture Sensing and Monitoring

Optical fiber sensor using sol gel membrane incorporated RTV silicon rubber was fabricated and developed for the characterization of dissolved oxygen in aqueous solution. The sol gel materials used consists of Tetraethylorthosilicate (TEOS) and Triethoxyoctylsilane (Octyl-triEOS) as the precursor compound for the preparation of the sol gel structures, while tris-BP Ruthenium (II) chloride as the fluorescent lifetime of the oxygen indicator. Dip coating techniques is utilized to position the sol gel technology at the distal end of the optical fiber. Dissolved oxygen gas sensor characterizations include a study on the sensitivity, temperature effects and drift rate of the sensor performance when measured in 40ppt salt water. Potential applications of the optical fiber sensor are including aquaculture, river monitoring and environment sector.     

A fiber-optic evanescent wave sensor for dissolved oxygen detection based on novel hybrid fluorinated xerogels immobilized with [Ru(bpy)3]2+

We have prepared a novel fiber-optic evanescent wave sensor (FEWS) for dissolved oxygen (DO) detection. The sensor fabrication was based on coating a decladded portion of an optical fiber with a microporous coating, which was prepared from 3,3,3-trifluoropropyltrimethoxysilane and n-propyltrimethoxysilane. The fluorophores were immobilized in the porous coating and excited by the evanescent wave field produced on the core surface of the optical fiber. The sensitivity of the sensor was quantified by the ratio of the fluorescence intensities in pure deoxygenated (I ₀) and in pure oxygenated environments (I). Results show that the quenching response of DO is increased with the enhancement of the coating surface hydrophobicity using the presented hybrid fluorinated ORMOSILs. The calibration curve of I ₀/I to [O₂] is linear from 0 to 40 ppm and the detection limit is 0.05 ppm (3σ) with a short response time of 15 s for DO detection. Figure       

A selective optical chemical sensor for o-nitrophenol based on fluorescence quenching of curcumin

An optical chemical sensor has been prepared for the selective determination of o-nitrophenol in aqueous solutions based on the fluorescence quenching of curcumin in PVC membrane. The sensing mechanism of the proposed sensor for o-nitrophenol has been discussed in detail. The fluorescence changes of sensing membrane resulted from an associated complex formation between curcumin and o-nitrophenol. In pH 4.8 buffer solution, the sensor responds linearly in the measuring range from 1.0 x 10(-2) mol 1(-1) to 1.5 x 10(-4) mol 1(-1), and the experimental detection limit is evaluated to be 8.0 x 10(-5) mol 1(-1). A stable signal was obtained within less than 1.5 min. Under the optimum conditions, the sequence of selective response to the sensing membrane is o-nitrophenol > 2,4-dinitrophenol > m-nitrophenol > p-nitrophenol > 2,4,6-trinitrophenol. Phenol, aniline as well as other ions have less effect on the fluorescence of the sensor. The reproducibility for the determination of o-nitrophenol is better than 1%, and the response is reversible. The sensor can be used for the determination of o-nitrophenol in water samples.     

刚果红交联聚乙烯醇薄膜／K^＋交换玻璃光波导检测氯化氢气体

用环氧氯丙烷为交联剂合成了刚果红(CR)交联聚乙烯醇(PVA)CR-PVA敏感试剂.用匀胶机将其做成薄膜固定在钾离子交换玻璃光波导表面,研制出一种光波导氯化氢气体传感器.CR-PVA薄膜碱式结构的最大吸收波长在600 nm以下,对波长为632.8 nm的激光吸收很弱;薄膜与酸性气体发生反应后强烈吸收波长在632.8 nm附近的导波或消失波;检测输出光强度的变化,即能够测出酸性气体浓度.测试结果表明,本传感器对低浓度HCl气体有快速响应,且对1.6～192 mg/m3范围内有良好的线性响应;SO2、NO2气体的浓度大于18000 mg/m3时才有响应,而对于高、低浓度H2S气体均无响应.     

以Sephadex为基质的光纤铜传感器的研究

本文发展了一种新的光纤铜传感器, 用DEAE Sephadex为基质, 通过电价键固定亚硝基红盐作为指示剂, 该传感层在520nm波长下, 反射光强度的变化与铜离子的浓度呈函数关系。用流动法和平衡法对传感器特性进行了研究, 响应时间为5秒,且可逆性好, 已成功应用于自来水和废水中痕量铜离子的直接测定。     

Integrated-optic ammonia sensor

Fibre coupled optical sensors for chemical and biologial species are important for process control, environmental control and pollution detection. An integrated optic ammonia sensor is described here; this is based on evanescent field absorption. The sensitive element of this sensor is a strip waveguide, fabricated by field assisted ion exchange, coated with a immobilized indicator dye. The sensor has a short response time and a long lifetime. An experimental arrangement is shown which has been built up for the characterization of different integrated optic sensor elements. Spectral response characteristics, response times and the generation of reference signals are reported in detail. The simple temperature dependence, the humidity independence and the very low cross sensitivity of this ammonia sensor is illustrated.     

Starch-iodine films respond to water vapor

Starch-iodine indicator films were found to have useful spectroscopic properties for the detection of water vapor. The large colorimetric response of these easily prepared films was easily detected by the absorption of 632.8 nm HeNe laser light, using a planar integrated optical waveguide (IOW) platform. The detection limit of a prototype sensor was found to be below 5% relative humidity (RH), with response times of the order of seconds.     

Zeolite-fiber integrated optical chemical sensors for detection of dissolved organics in water

MFI zeolite coated optical fiber sensors have been developed for in situ detection of dissolved organics in water. The sensors operate by monitoring the optical reflectivity changes caused by the selective adsorption of organic molecules, i.e., 2-propanol or pentanoic acid in this study, from aqueous solutions in the zeolitic pores. Reversible and monotonic sensor signals were observed in response to the variation of 2-propanol concentration in water with fast response. However, the sensor exhibited a much slower response to pentanoic acid than to 2-propanol. It was also found that substitution of Si by Al in the MFI framework increased the adsorption of pentanoic acid that resulted in enhanced sensor responses.     

Development of a modified grating coupler in application to geosciences

A grating coupler system has been developed to measure refractive index gradients with high spatial (6.7 μm) and temporal (milliseconds) resolution. The system was applied to two-phase model systems consisting of water and non-aqueous pollution liquids. Refractive index gradients at the interfaces between the aqueous and organic phase of 1-butanol, hexane, and 1-heptanol were monitored under steady-state conditions. The temporal resolution was utilized in diffusion experiments with glycerol and sodium chloride in water, where the formation of a concentration gradient was studied. In a further application, the grating coupler system was modified to monitor low-level concentrations of aqueous pollution profiles as are caused by bacterial degradation in the aqueous phase. Toluene was selected as contaminant. The sensor sensitivity was improved by coating the sensor with the pre-concentrating polymers polydimethylsiloxane and Teflon® AF-2400. With the grating coupler setup, a multi-purpose instrument was created to measure high-resolution refractive index gradients with high temporal and spatial resolution in different fields of application. The new sensor system can be used to measure absolute refractive indices by covering parts of the sensing area with cover media of known refractive index. Coatings can be used for sensitivity improvement by pre-concentrating the sample, for selectivity by utilizing filtering properties of the coating, and as calibration standard for absolute refractive index measurements.     

Synthesis of ZrO2-carbon nanotube composites and their application as chemiluminescent sensor material for ethanol

ZrO2-carbon nanotube (CNT) composites have been successfully synthesized via decomposition of Zr(NO3)4.5H2O in supercritical carbon dioxide-ethanol solution with dispersed CNTs at relatively low temperatures. The samples were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction spectroscopy (XRD), transmission electron microscopy (TEM), and energy-dispersive X-ray (EDX) analyses. It was demonstrated that CNTs were fully coated with an amorphous ZrO2 layer, and the coating layer was nominally complete and uniform. In addition, the thickness of the coating sheath could be readily controlled by tuning the Zr(NO3)4.5H2O/CNTs ratio used. Furthermore, the chemiluminescent sensor prepared from ZrO2-carbon nanotube composites exhibited dramatic sensitivity as well as high stability and selectivity to ethanol.     

Special susceptive aqueous ammonia chemi-sensor: extended applications of novel UV-curable polyurethane-clay nanohybrid

In this contribution, chemical sensor for the detection of aqueous ammonia has been fabricated using UV-curable polyurethane acrylate (PU) and nanohybrids (NH-1, NH-3 and NH-5). PU has been prepared by reacting polycaprolactone triol (PCLT) and isophorone diisocyanate (IPDI) while the nanohybrids, NH-1, NH-3, and NH-5 have been synthesized by solution blending method using PU with 1, 3, and 5 wt% loading levels of C-20B. PU and their nanohybrids showed higher sensitivity investigated by I-V technique using aqueous ammonia as a target chemical. All the nanohybrids showed higher sensitivity as compared to neat PU. The sensitivity increased with increase in clay content and the nanohybrid containing 5 wt% of clay showed the highest sensitivity (8.5254 μA cm⁻² mM⁻¹) with the limit of detection (LOD) of 0.0175 ± 0.001 μM, being 7.8 times higher than pure PU. The calibration plot for all the sensors was linear over the large range of 0.05 μM to 0.05 M. The response time of the fabricated sensor was <10.0 s. Therefore, one can fabricate efficient aqueous ammonia sensor by utilization of nanohybrid as an efficient electron mediator.     

High swelling gels for sensing applications

Crosslinked hydrophilic polymers of different chemical structures can be used as sensor coatings for the detection of gaseous analytes. If their crosslink density is low, these materials behave in aqueous media as soft hydrogels with high swelling capacity. From a physico-mechanical standpoint, they are amorphous rubber-like materials, with high flexibility of their macromolecular chains. This property is particularly significant in view of applications in the sensors field, because it favours diffusion of the analyte molecules through the coating layer. This paper deals with the application of poly(ethylene glycols) (PEG)- and poly(N-vinylpyrrolidinone) (PVP)-based crosslinked resins as relative humidity (RH) sorbing materials, and of a poly(amidoamine)(PAA)-based resin as SO₂-sorbing material. The electronic devices used for evaluating the sorption capability of these polymeric coatings were gravimetric resonant sensors. Resins of various crosslink density, and therefore of various swelling ratios in water, were purposely prepared and characterized. Thin coating, layers, prepared by casting from dilute aqueous suspensions of the resins, previously micronized in water, were used for sorption experiments. All experiments were performed in controlled RH and temperature environments.