Fiber Evanescent Wave Spectroscopy Research Articles

From Selenium- to Tellurium-Based Glass Optical Fibers for Infrared Spectroscopies

Chalcogenide glasses are based on sulfur, selenium and tellurium elements, and have been studied for several decades regarding different applications. Among them, selenide glasses exhibit excellent infrared transmission in the 1 to 15 µm region. Due to their good thermo-mechanical properties, these glasses could be easily shaped into optical devices such as lenses and optical fibers. During the past decade of research, selenide glass fibers have been proved to be suitable for infrared sensing in an original spectroscopic method named Fiber Evanescent Wave Spectroscopy (FEWS). FEWS has provided very nice and promising results, for example for medical diagnosis. Then, some sophisticated fibers, also based on selenide glasses, were developed: rare-earth doped fibers and microstructured fibers. In parallel, the study of telluride glasses, which can have transmission up to 28 µm due to its atom heaviness, has been intensified thanks to the DARWIN mission led by the European Space Agency (ESA). The development of telluride glass fiber enables a successful observation of CO2 absorption band located around 15 µm. In this paper we review recent results obtained in the Glass and Ceramics Laboratory at Rennes on the development of selenide to telluride glass optical fibers, and their use for spectroscopy from the mid to the far infrared ranges.

Identification of foodborne pathogens within food matrices by IR spectroscopy

Fiber evanescent wave spectroscopy (FEWS) was used to classify various foodborne pathogens ( Listeria monocytogenes, Staphylococcus aureus and Salmonella enteritidis) using chemometric methods such as principal component analysis (PCA) and logistic-partial least squares (logistic-PLS). Spectra were recorded thanks to an IR optical fiber made of chalcogenide glasses. A limited segregation between the healthy and non healthy food has been observed using the PCA method, whereas a clear differentiation between bacteria strains was obtained using the PLS regression. FEWS coupled to chemometric methods is a promising technique for the identification of foodborne pathogens as it could provide a rapid identification and classification of the bacteria.

Selenium modified GeTe 4 based glasses optical fibers for far-infrared sensing

This study reports on the synthesis of telluride glasses that have transmission far beyond the second atmospheric window and are stable enough toward crystallisation to be drawn into optical fiber. These glasses are based on the GeTe 4 initial composition which has been stabilized by the introduction of few percents of Se and a modified the Te/Ge ratio. In that domain, Ge 21Se 3Te 76 constitute the optimum composition and some mono index optical fibers have been successfully drawn. It is shown that their optical transparencies extend from 5 to almost 16 μm in the mid-infrared, establishing a record for chalcogenide glass fibers. These fibers have been used to implement Fiber Evanescent Wave Spectroscopy experiments, permitting to detect infrared molecule signatures beyond 12 μm, infrared domain that was unreachable by now. These innovative fibers are also used to detect the broad absorption band of gaseous CO 2 lying from 13 to 16 μm and therefore hold promises in the framework of the Darwin mission of the European Space Agency. Both of these results suggest that these new optical fibers will become essential in the field of infrared remote sensing.

CO2 Detection Using Microstructured Chalcogenide Fibers

In this work, detection in the mid-infrared (mid-IR) of carbon dioxide, so called greenhouse gas, using Fiber Evanescent Wave Spectroscopy (FEWS) technique is investigated. Since each pollutant gas shows a characteristic optical absorption spectrum in the mid-infrared, it is possible to detect selectively and quantitatively the presence of gases in a given environment by analysing mid-IR spectra. The main infrared signature of carbon dioxide gas consist in a double absorption peak located at 4.26 μm. Chalcogenide optical fibres, transmitting light in the 1-6 μm range, are well-adapted for CO2 analysis. Thus, tapered and microstructured chalcogenide fibers have especially been designed for CO2 detection. They present low optical losses in the spectral region of the CO2 absorption band. The fabrication of tapered and microstructured fibers is reported. Then, using a tapered fiber the detection limit of CO2 is around 20 vol.%. On the other hand, for the first time to our knowledge, the detection of gas in the mid-infrared is demonstrated with a chalcogenide microstructured fiber.

Polymerisation of an industrial resin monitored by infrared fiber evanescent wave spectroscopy

In order to monitor the polymerisation process of an industrial resin, a study by infrared fiber evanescent wave spectroscopy has been carried out. To design the optical fiber, a special glass composition has been optimized in the Se–Sb–Ge–Ga vitreous quaternary system. This glass exhibits a large transparency in the mid-infrared range, and shows a temperature–viscosity behaviour that enables the preparation of optical fibers. Most important is the glass transition temperature, which is high enough to allow fiber measurement at about 200 °C. Infrared spectra have been recorded every 5 min during the curing process of the resin. A direct measurement of the integrated intensities of the relevant absorption band enabled to determine the times when the curing process started and when it finished. This direct analysis has been confirmed by principle component analysis, which is an unsupervised and very efficient method for applications at the industrial scale. Moreover, it has been shown that an autocatalytic kinetic model should be used to give a good account for the absorbency evolution versus time. From a practical point of view, the optical fiber can be integrated directly into the mould and be considered as a consumable. The use of chalcogenide glass fiber to record remotely infrared signals, coupled with modern spectral analysis techniques constitute a very powerful route for monitoring the curing of thermo-hardening resins.

Fiber evanescent wave spectroscopy using the mid-infrared provides useful fingerprints for metabolic profiling in humans

Fiber evanescent wave spectroscopy (FEWS) explores the mid-infrared domain, providing information on functional chemical groups represented in the sample. Our goal is to evaluate whether spectral fingerprints obtained by FEWS might orientate clinical diagnosis. Serum samples from normal volunteers and from four groups of patients with metabolic abnormalities are analyzed by FEWS. These groups consist of iron overloaded genetic hemochromatosis (GH), iron depleted GH, cirrhosis, and dysmetabolic hepatosiderosis (DYSH). A partial least squares (PLS) logistic method is used in a training group to create a classification algorithm, thereafter applied to a test group. Patients with cirrhosis or DYSH, two groups exhibiting important metabolic disturbances, are clearly discriminated from control groups with AUROC values of 0.94+/-0.05 and 0.90+/-0.06, and sensibility/specificity of 8684% and 8787%, respectively. When pooling all groups, the PLS method contributes to discriminate controls, cirrhotic, and dysmetabolic patients. Our data demonstrate that metabolic profiling using infrared FEWS is a possible way to investigate metabolic alterations in patients.

Potential of ‘flat’ fibre evanescent wave spectroscopy to discriminate between normal and malignant cells in vitro

The present study focuses on evaluating the potential of flattened AgClBr fibre-optic evanescent wave spectroscopy (FTIR-FEWS) technique for detection and identification of cancer cells in vitro using cell culture as a model system. The FTIR-FEWS results are compared to those from FTIR-microspectroscopy (FTIR-MSP) method extensively used to identify spectral properties of intact cells. Ten different samples of control and malignant cells were measured in parallel by the above two methods. Our results show a significant similarity between the results obtained by the two methodologies. The absorbance level of Amide I/Amide II, phosphates and carbohydrates were significantly altered in malignant compared to the normal cells using both systems. Thus, common biomarkers such as Amide I/Amide II, phosphate and carbohydrate levels can be derived to discern between normal and cancer cells. However, marked differences are also noted between the two methodologies in the protein bands due to CH3 bending vibration (1480-1350 cm(-1)). The spectral differences may be attributed to the variation in the penetration depth of the two methodologies. The use of flattened fibre rather than the standard cylindrical fibre has several practical advantages and is considered as an important step towards in vivo measurements in real time, such as that of skin nevi and melanoma using special designs of fibre-optic-based sensors.

Infrared biosensors using hydrophobic chalcogenide fibers sensitized with live cells

Chalcogenide glass fibers are used to perform remote infrared analysis in a fiber evanescent wave spectroscopy system (FEWS). Spectral analysis of a series of organic species demonstrates that the detection signal of non-polar species is enhanced by up to 60% relative to that of water. Contact angle measurements of the organic liquid/glass interaction strength shows that the spectral enhancement is the result of glass surface hydrophobicity. The greater interaction of non-polar species with the chalcogenide surface leads to a concentration gradient of the organic species at the glass surface where the evanescent wave is most intense. This results in selective detection of non-polar organic species in aqueous solution using FEWS. This behavior is beneficial for the detection of microorganism by FEWS and is used to design bio-optic sensors based on monitoring the response of live cells to toxins by detecting change in their infrared spectrum. This technique permits observation of disruption induced in living mammalian cells by at least two different types of toxicants. It is shown that it is possible to distinguish between the effect of a genotoxic agent (which damage nucleic acids) and a cytotoxic agent (which damages other cellular components) based on the cell's IR response.

Evaluation of Toxic Agent Effects on Lung Cells by Fiber Evanescent Wave Spectroscopy

Biochemical changes in living cells are detected using a fiber probe system composed of a single chalcogenide fiber acting as both the sensor and transmission line for infrared optical signals. The signal is collected via evanescent wave absorption along the tapered sensing zone of the fiber. We spectroscopically monitored the effects of the surfactant Triton X-100, which serves as a toxic agent simulant on a transformed human lung carcinoma type II epithelial cell line (A549). We observe spectral changes between 2800-3000 cm(-1) in four absorptions bands, which are assigned to hydrocarbon vibrations of methylene and methyl groups in membrane lipids. Comparison of fiber and transmission spectra shows that the present technique allows one to locally probe the cell plasma membrane in the lipid spectral region. These optical responses are correlated with cellular metabolic activity measurements and LDH (lactate dehydrogenase) release assays that indicate a loss of cellular function and membrane integrity as would be expected in response to the membrane solubilizing Triton. The spectroscopic technique shows a significantly greater detection resolution in time and concentration.

Monitoring of pollutant in waste water by infrared spectroscopy using chalcogenide glass optical fibers

Infrared optical fibers based on chalcogenide glass are used as sensor for the determination of volatile organic pollutants in groundwater. The system work following the fiber evanescent wave spectroscopy principle, so-called fiber evanescent wave spectroscopy (FEWS). It was tested in situ, in real time, under real-world conditions. The measurement set-up consisted of a FTIR spectrometer (BRUKER V22), coupled with the fiber (about 2 m), and a cooled mercury–cadmium–telluride detector. A special kit provided by Bruker was connected on the spectrometer to focus the infrared beam from the black body at the entry of the fiber. Some preliminary pilot scale tests, led in an artificial aquifer, show that the fiber permits access to the absorption line positions in a wide range from 4000 to 800 cm −1 . Moreover, it is shown that the original design of the fiber enables detection of weak concentrations of pollutants down to 1 ppm of C 2 Cl 4 . Then the experiments in “real-world” conditions are carried out after having applied a proper protection on the fibers. A comparison with the chemical analysis data shows that the optical fibers enable to follow the evolution of pollutant rates in water versus time. Finally, this work is promising in view of installing some permanent checking devices into wells to control the rate of pollutants in groundwater of landfill.

Monitoring of pollutant in waste water by infrared spectroscopy using chalcogenide glass optical fibers

Infrared optical fibers based on chalcogenide glass are used as sensor for the determination of volatile organic pollutants in groundwater. The system work following the fiber evanescent wave spectroscopy principle, so-called fiber evanescent wave spectroscopy (FEWS). It was tested in situ, in real time, under real-world conditions. The measurement set-up consisted of a FTIR spectrometer (BRUKER V22), coupled with the fiber (about 2m), and a cooled mercury–cadmium–telluride detector. A special kit provided by Bruker was connected on the spectrometer to focus the infrared beam from the black body at the entry of the fiber. Some preliminary pilot scale tests, led in an artificial aquifer, show that the fiber permits access to the absorption line positions in a wide range from 4000 to 800cm−1. Moreover, it is shown that the original design of the fiber enables detection of weak concentrations of pollutants down to 1ppm of C2Cl4. Then the experiments in “real-world” conditions are carried out after having applied a proper protection on the fibers. A comparison with the chemical analysis data shows that the optical fibers enable to follow the evolution of pollutant rates in water versus time. Finally, this work is promising in view of installing some permanent checking devices into wells to control the rate of pollutants in groundwater of landfill.

Optical analysis of infrared spectra recorded with tapered chalcogenide glass fibers

Abstract Infrared fiber evanescent wave spectroscopy (FEWS) spectra of water–ethanol mixtures are recorded and reconstructed thanks to a causal dispersion analysis technique. The complete expression of the complex reflection coefficients was used to determine the transmitted signal. The problems of shifting peaks or overlapping absorption bands from different chemical are well addressed. The effect of several parameters on the absorbance, such as the length of immersion and the diameter of the fiber probe have been calculated and fit well with experimental data. More generally, the agreement between experimental and calculated spectra suggest the presented analysis technique is more accurate than other current analysis techniques.

Chalcogenide double index fibers: fabrication, design, and application as a chemical sensor

Double index chalcogenide fibers, based on tellurium, arsenic, and selenium, have been made by an original technique. This technique, based on the build-in-casting method, is achieved in a sealed silica ampoule. In view of the low attenuation obtained in the mid-infrared (IR), these fibers are used to implement Fiber Evanescent Wave Spectroscopy (FEWS). As the IR light is only propagated through the core of the waveguide, a chemical etching is applied in order to remove the glassy cladding of the sensing zone. IR spectra of ethanol and chloroform, recorded with such sensor, are presented showing the high sensitivity of the method.

In situ infrared fibre evanescent wave spectroscopy as adiagnostic tool for plasma polymerization in a gas discharge

A novel diagnostic technique is proposed for the in situsensing of thin organic film deposition in gas discharge plasmas. The methodis based on the evanescent wave spectroscopy using an infrared fibre, andallows one to analyse the molecular structure of a growing plasma polymer filmin the process reactor. The styrene plasma polymerization on a fibre in theplasma bulk of a capacitively coupled rf discharge was studied. The infraredfibre sensor provides higher sensitivity than the crystals of comparablegeometry usually employed in attenuated total reflection spectroscopy.Accumulated evanescent wave infrared absorption spectra give information notonly on the molecular structure of the deposited films, but also on its timeevolution during the deposition. It was also possible to make conclusions onthe molecular orientation of plasma polymerized styrene films deposited underthe various process conditions. The fibre was regenerated in an oxygenplasma. The etching process results in the destruction of phenyl rings andthe ablation of the plasma polymer film from the surface of the fibre core.

Towards a remote IR fiber-optic sensor system for the determination of chlorinated hydrocarbons in water

A laboratory prototype of a mid-infrared (MIR) fiber-optic sensor system capable of remote on-site and real-time determination of chlorinated hydrocarbons (CHCs) in water has been developed. The system is based upon fiber evanescent-wave spectroscopy (FEWS) and consists of silver halide fibers that are coupled to a portable Fourier transform infrared (FTIR) spectrometer. These fibers serve both as signal transfer lines and as sensing elements. In the latter case they are coated with thin films of ethylene/propylene copolymer for the purposes of enrichment of the analytes and exclusion of water. A detection limit for tetrachloroethylene of 300 ppb has been achieved with a total contact time between sample and sensor of 10 min.

Development of protective polymer coatings for silver halide fibers and their application as threshold level sensors for chlorinated hydrocarbons in sea water

The stability of silver halide fibers in artificial sea water (ASW) with and without a protective polymer coating and the influence of high salt concentrations on the sensor response was investigated. In contrast to bare silver halide fibers, the polymer coated fibers remain stable in contact with chloride solutions. This enables the application of a recently presented mid-IR fiber evanescent wave spectroscopy (FEWS) sensor system for the quantitative detection of chlorinated hydrocarbons (CHC) also in sea water.

New IR Fiber-Optic Chemical Sensor for in Situ Measurements of Chlorinated Hydrocarbons in Water

In this work the development and validation of a new MIR fiber-optic physicochemical sensor system for the continuous in situ analysis of chlorinated hydrocarbons (CHCs) in water is described. This study took advantage of the selectivity and sensitivity of fiber evanescent wave spectroscopy (FEWS) and the recent development of polycrystalline silver halide fibers. Since these fibers are transparent up to 20 μm, it was possible for the first time to develop a fiber-optic sensing system for CHCs, which have their strongest absorption bands > 10 μm. The silver halide fibers were coated with low-density polyethylene (LDPE) to enrich the CHC within the evanescent wave and to exclude the IR absorbing water from the measurement. For the quantitative in situ FEWS measurements, the coated silver halide fibers were coupled to a Fourier transform infrared (FT-IR) spectrometer using an off-axis parabolic mirror and a fiber-detector coupling system. This setup enabled the simultaneous in situ detection of the most common chlorinated hydrocarbons in concentrations between 1 to 50 mg/L in water by employing a fiber sensing part only 10 cm in length. A comparative analysis of waste water samples under participation of two experienced head space-gas chromatography (HSGC) laboratories showed good agreement of this continuous sensor system with the established standard techniques. The resulting working curve for tetrachloroethylene showed a correlation coefficient of r2 = 0.968 and a relative standard deviation of 17% in the range from 1 to 10 ppm.

Simultaneous in-situ trace-analysis of several chlorinated hydrocarbons in water with an IR fiber optical system

The principles of coating silver halide fibers with polymers was used to analyze different chlorinated hydrocarbons in water simultaneousely. The sensing system, based on Fiber Evanescent Wave Spectroscopy (FEWS), was composed of a mid infrared (MIR) transparent silver halide fiber coupled to a Fourier Transform Infrared (FTIR) spectrometer and enabled the detection of the most widespread organochlorides in the lower ppm-range due to their specific absorptions in the MIR-range.