Fiberoptic Evanescent Wave Spectroscopy Research Articles

Non-destructive and in-situ detection of shrimp freshness using mid-infrared fiber-optic evanescent wave spectroscopy.

There is strong interest in non-destructive and rapid determination of food freshness in food research. In this study, mid-infrared (MIR) fiber-optic evanescent wave (FOEW) spectroscopy was applied to monitor shrimp freshness through the evaluation of protein, chitin, and calcite contents in conjunction with a Partial Least Squares Discriminant Analysis (PLS-DA) model. Shrimp shells were wiped with a micro fiber-optic probe to obtain a FOEW spectrum which quickly and nondestructively allowed evaluation of the shrimp freshness. Peaks for proteins, chitin, and calcite, which are closely related to shrimp freshness, were detected and quantified. Compared with the standard indicator for evaluating shrimp freshness (total volatile basic nitrogen), the PLS-DA model gave recognition rates for shrimp freshness using calibration and validation sets of the FOEW data of 87.27%, 90.28%, respectively. Our results show that FOEW spectroscopy is a feasible method for non-destructive and in-site detection of shrimp freshness.

Recent Achievements in Development of Chalcogenide Optical Fibers for Mid-IR Sensing

Recent results of research of passive and active optical waveguides made of high-purity chalcogenide glasses for middle infrared fiberoptic evanescent wave spectroscopy of liquid and gaseous substances are presented. On the basis of selenide and telluride glass fibers, novel types of highly sensitive fiber probes are developed. On the basis of Pr(3+)- and Tb(3+)-doped Ga(In)-Ge-As-Se and Ga-Ge-Sb-Se glass fibers, the 4.2–6 μm wavelength radiation sources are created for all-fiber sensor systems. Successful testing of chalcogenide glass fiber sensors for the analysis of some liquid and gaseous mixtures was carried out.

In situ detection of fruit spoilage based on volatile compounds using the mid-infrared fiber-optic evanescent wave spectroscopy.

Volatile compounds such as ethanol released from fruit can be rapidly detected using Fourier Transform Infrared spectroscopy based on a long-path gas cell. However, this method relies on a long optical path length and requires pumping fruit volatiles into the gas cell. This can lead to the volatile compounds being contaminated and not detectable in situ. Fiber optic evanescent wave spectroscopy (FOEW) is not influenced by the path length so can detect materials (solid, liquid and gas phase) rapidly in situ, using only a few millimeters of optical fiber. In the present study, a spiral silver halide FOEW sensor with a length of approximately 21 mm was used to replace a long-path gas cell to explore the feasibility of identifying volatile compounds released from grapes in situ. The absorption peaks of ethanol in the volatile compounds were clearly found in the FOEW spectra and their intensity gradually increased as the storage time of the grapes increased. PCA analysis of these spectra showed clear clustering at different storage times (1-3, 4-5 and 6-7 d), revealing that the concentration of the ethanol released from the grapes changed significantly with time. The qualitative model established by PLS-DA algorithm could accurately classify grape samples as “Fresh,” “Slight spoilage,” or “Severe spoilage”. The accuracy of the calibration and validation sets both were 100.00%. These changes can therefore be used for rapidly identifying fruit deterioration. Compared with the method used in a previous study by the authors, this method avoids using a pumping process and can thus identify volatile compounds and hence monitor deterioration in situ and on-line by placing a very short optical fiber near the fruit.

Technical Note: Noninvasive mid-IR fiber-optic evanescent wave spectroscopy (FEWS) for early detection of skin cancers.

Melanoma is the most lethal of the three primary skin cancers, including also basal cell carcinoma (BCC) and squamous cell carcinoma (SCC), which are less lethal. The accepted diagnosis process involves manually observing a suspicious lesion through a Dermascope (i.e., a magnifying glass), followed by a biopsy. This process relies on the skill and the experience of a dermatologist. However, to the best of our knowledge, there is no accepted automatic, noninvasive, and rapid method for the early detection of the three types of skin cancer, distinguishing between them and noncancerous lesions, and identifying each of them. It is our aim to develop such a system. We developed a fiber-optic evanescent wave spectroscopy (FEWS) system based on middle infrared (mid-IR) transmitting AgClBr fibers and a Fourier-transform infrared spectrometer (FTIR). We used the system to perform mid-IR spectral measurements on suspicious lesions in 90 patients, before biopsy, in situ, and in real time. The lesions were then biopsied and sent for pathology. The spectra were analyzed and the differences between pathological and healthy tissues were found and correlated. Five of the lesions measured were identified as melanomas, seven as BCC, and three as SCC. Using mathematical analyses of the spectra of these lesions we were able to tell that all were skin cancers and we found specific and easily identifiable differences between them. This FEWS method lends itself to rapid, automatic and noninvasive early detection and characterization of skin cancers. It will be easily implemented in community clinics and has the potential to greatly simplify the diagnosis process.

Monitoring Corrosion Processes via Visible Fiber-Optic Evanescent Wave Sensor

Ferrous objects, especially those that are additionally exposed to harsh environments, e.g., high humidity, have the common problem of suffering aggressive corrosion processes. Without a precaution, this leads in many cases to a limited functionality followed by treatment steps, and expensive repairing costs, as well as to defects/uselessness and even to safety problems, e.g., bridge-collapsing, escaping gas and liquids from pipelines, or leaking oil tankers destroying the ecological system. Conventionally applied methods are confined to laboratory use due to bulky instruments, and are, therefore, time-intensive and may cause erroneous results. Therefore, a sensor based on fiber-optic evanescent wave spectroscopy (FEWS) working in the visible spectral range was developed. The sensor system is comprised of an uncoated single crystal sapphire fiber as a waveguide operating in the visible spectral range in combination with a laser diode as a light source at a specific wavelength and a photodiode for signal detection. Within this study, the potential of the developed sensor was investigated. The corrosion process was simulated by implementing a corroded iron bar inside the measuring cell. When corrosion starts, iron ions are released leading to a complexation reaction with the dye. The results showed the potential use of the developed sensor system enabling implementation for online and on-site detection and monitoring of components susceptible to corrosion.

Toward the Required Detection Limits for Volatile Organic Constituents in Marine Environments with Infrared Evanescent Field Chemical Sensors.

A portable sensor system for the simultaneous detection of multiple environmentally relevant volatile organic compounds (VOCs) in real seawater based on Fourier transform infrared fiber-optic evanescent wave spectroscopy (FT-IR-FEWS) was developed. A cylindrical silver halide (AgX) fiber with an ethylene/propylene copolymer (E/P-co) coated flattened segment was used as an active optical transducer. The polymer membrane enriches the hydrophobic analytes, while water is effectively excluded from the penetration depth of the evanescent field. Determination of multicomponent mixtures (i.e., 10 VOCs in real-world seawater samples) collected in Arcachon Bay, France revealed a high accuracy and reproducibility with detection limits down to 560 ppb. The measurement showed no significant influence from changing water conditions (e.g., salinity, turbidity, and temperature or other interfering substances). The time constants for 90% saturation of the polymer ranged from 20 to 60 min. The sensor system is capable of being transported for on-site monitoring of environmental pollutants in aqueous matrices with efficient long-term stability, thus showing great potential to be utilized as an early warning system.

Optical fibers based on special pure Ge20Se80 and Ge26As17Se25Te32 glasses for FEWS

For middle infrared fiber-optic evanescent wave spectroscopy, the single-index Ge20Se80 and Ge26As17Se25Te32 glass fibers are fabricated by a crucible method. The background optical loss in the Ge20Se80 fiber is 1.5 dB/m in the 5–7.8 μm spectral range (minimum is 0.9 dB/m at 7.1 μm), and that in the Ge26As17Se25Te32 fiber is 1 dB/m in the range of 5.5–8.5 μm (minimum is 0.65 dB/m at 6.6 μm). On the basis of these chalcogenide glass fibers, the middle infrared sensors with the different geometry of sensitive zone (straight, U-shaped form, one loop, two loops) are manufactured. By the example of diesel fuel, it is shown that when passing from the straight section of the sensitive zone to the double loop, the integrated intensity of the absorption bands increases by an order of magnitude. The method of regression analysis was applied to plot a calibration dependence for the additive concentration in diesel fuel in the range of 0.1–1 vol% using a U-shaped fiber sensor. The possibility of using the luminescent Pr(3+)-doped chalcogenide fiber as the source of mid-IR radiation for recording the absorption spectra of substances absorbing in the spectral range 4–5 μm is demonstrated.

Fiber-optic evanescent wave spectroscopy (FEWS) of crystals from a urine sample as a tool for evaluating the chemical composition of kidney stones

One in every 20 people develops kidney stones at some point in their life.

Optical Characterization of Commercial Lithiated Graphite Battery Electrodes and in Situ Fiber Optic Evanescent Wave Spectroscopy.

Optical characterization of graphite anodes in lithium ion batteries (LIB) is presented here for potential use in estimating their state of charge (SOC). The characterization is based on reflectance spectroscopy of the anode of commercial LIB cells and in situ optical measurements using an embedded optical fiber sensor. The optical characterization of the anode using wavelengths ranging from 500 to 900 nm supports the dominance of graphite over the solid electrolyte interface in governing the anode's reflectance properties. It is demonstrated that lithiated graphite's reflectance has a significant change in the near-infrared band, 750-900 nm, compared with the visible spectrum as a function of SOC. An embedded optical sensor is used to measure the transmittance of graphite anode in the near-infrared band, and the results suggest that a unique inexpensive method may be developed to estimate the SOC of a LIB.

Flattened infrared fiber-optic sensors for the analysis of micrograms of insoluble solid particles in solution or in a dry state

Highly sensitive absorption measurements on various samples may be carried out by Fiber-optic Evanescent Wave Spectroscopy (FEWS) in the mid-IR. Such measurements have already been done on solids, liquids and gases, using chalcogenide glass fibers or crystalline fibers. Segments of crystalline AgClBr fibers may be used as sensors of much higher sensitivity if their middle sections are pressed to form flat waveguides. We carried out measurements on micrograms of insoluble or slightly soluble particles in water, when they sedimented on the flattened parts of such sensors. Measurements were also carried out on few micrograms of dry particles that had been pressed onto the flattened parts. Flattened fiber sensors may therefore be used for measurements on micrograms of particles and they can be used for identifying the chemical nature of particles of organic, inorganic or biological materials and for studying their properties. The FEWS method, based on flattened mid-IR fiber sensors, is simple, inexpensive and does not require sample processing. It would be useful for measurements on very small quantities of particles for biomedical applications, for environmental protection, for drug enforcement agencies and for homeland security.

Fiber-optic probes enable cancer detection with FTIR spectroscopy

Fourier transform infrared spectroscopy (FTIR) reveals biochemical 'fingerprints' and has found disease patterns in excised human tissues. Fiber-optic probes have been developed for FTIR in living systems, allowing for cancer detection. There are challenges to making in vivo FTIR a reality, which are being addressed through hardware advances, determining key wavelengths and tissue preparation. Fiber-optic evanescent wave spectroscopy (FEWS)-FTIR with endoscope-compatible fiber-optic silver halide probes is feasible, and could prove useful for distinguishing premalignant and malignant tissues from biopsies or within patients. Developments of smaller silver halide probes as well as in vivo tissue drying methods will move this approach closer to the clinic where it can be used for early cancer detection, disease characterization and guided biopsies.

The Investigation of Water Diffusion into Teflon Copolymer Revealed by Fiber-optic Evanescent Wave Spectroscopy

Fiber-optic evanescent wave infrared spectroscopy was used for the study of water diffusion in Teflon and has provided valuable information about the structure of water in amorphous hydrophobic polymers. Time-dependent absorption measurements were carried out in two spectral ranges: 3000-3800 cm(-1), associated with the O-H stretching mode, and 1620-1670 cm(-1), associated with the H-O-H bending mode of water. The results indicate that the IR spectra could be expressed as a superposition of spectra due to two species of water molecules: strongly and weakly hydrogen-bonded. We suggest that water molecules form clusters with strongly hydrogen-bonded molecules at the cores and with weakly hydrogen-bonded molecules at the external parts of the clusters. A mathematical model, based on a linear diffusion equation with a moving boundary, gave a ratio of 3.5 between the total number of molecules in a cluster and the number of water molecules at the core of the cluster.

Mid-Infrared Fiber-Optic Attenuated Total Reflection Spectroscopy of the Solid—Liquid Phase Transition of Water

Measurements of mid-infrared (MIR) absorption spectra of water and heavy water were carried out by fiber-optic evanescent wave spectroscopy, using silver halide (AgClBr) infrared fibers. Such measurements were performed for the first time on one sample, during the solid-liquid phase transition. From the variation of the spectra with temperature we found a new isosbestic point (at 3280 cm(-1) for H(2)O or at 2475 cm(-1) for D(2)O) and we identified five components of the O-H (O-D) stretch band. These phenomena have provided new information about the molecular structure of water.

Investigations of the Structure of Water Using Mid-IR Fiberoptic Evanescent Wave Spectroscopy

Liquid water is one of the most studied but still one of the least understood substances. The absorption spectra of water in the mid-IR were measured from -10 and up to 90 degrees C using fiberoptic evanescent wave spectroscopy. The changes in the spectrum and the existence of an isosbestic point during the ice-liquid phase transition were studied. Based on the spectroscopic data we propose a multispecies model for the structure of liquid water. The new model provides an explanation for the results of the measurements reported in this work. It also provides an explanation for some of the unique thermodynamic and kinetic properties of liquid water and for many of the anomalies of water.

Evanescent-wave infrared spectroscopy with flattened fibers as sensing elements.

Fiber-optic evanescent-wave spectroscopy (FEWS) is a novel method for measuring the absorption spectra of samples in contact with a segment of an optical fiber that serves as a sensing element. We used a cylindrical IR-transmitting AgClBr fiber whose central section, of length L, was flattened to a thickness d. This section was used as the FEWS sensing element. Our theoretical work predicted that the signals obtained in FEWS measurements should be linearly dependent on L and inversely proportional to d. Decreasing the thickness can significantly increase its sensitivity of the sensor. These theoretical results were verified experimentally by measurements of methanol and water.

Direct monitoring of soil and water nitrate by FTIR based FEWS or membrane systems.

The development of silver halide fibers that transmit with minimal loss into the mid-IR (MIR) paved the way to their successful utilization as effective ATR (Attenuated Total Reflectance) elements, promoting the implementation of Fiberoptic Evanescent Wave Spectroscopy (FEWS) for direct monitoring of nitrate in environmental systems. Samples containing nitrate in water, soil extracts, and pastes were used for the determination of nitrate concentration with a common ATR ZnSe crystal and with silver halide fibers (FEWS). Spectra of soil pastes and suspensions and those of phosphate, carbonate, sulfate, ammonium, and soil organic constituents were collected to study possible interference with nitrate determination. The standard error of estimate (SEE) and R2 values obtained with flat fibers, using the simple single-point correlation method, were superior to those obtained for cylindrical FEWS and ZnSe ATR crystals in pure water. A significant improvement in the SEE and R2 was achieved in most soil pastes by applying the simple mode of the Cross Correlation method. Direct transmission of MIR radiation through ion-exchange membranes, partially loaded with nitrate or carbonate, was found an effective alternative for MIR-FTIR determination of these ions. Further development and modification of the FEWS devices should allow in-situ and online determination of nitrate in soil and environmental systems.

A fiber optic biosensor (FOBS) to monitor mutans streptococci in human saliva

A fiber optic biosensor (FOBS) to monitor mutans streptococci activity in human saliva is developed. The biosensor utilizes e fiber optic evanescent wave spectroscopy to monitor a bacterial mediated biochemical reaction. To achieve this, a short length of the cladding is removed; the fiber core surface is treated and coated with a thin film of porous glass medium using sol–gel technique. The mutans streptococci mediated reaction with sucrose is monitored using a photosensitive indicator, which is immobilized within the porous glass coating. Spectroscopic analysis shows that the transmitted intensity at 597 nm increases conspicuously when monitored for 120 min. Two distinct phases are observed, one from 0 to 60 min and the other from 60 to 120 min. A negative correlation coefficient between the rate of increase in absorption peak intensity recorded by the FOBS and the decrease in pH measured using the pH meter, was calculated to be ρ=−0.994. This investigation highlights the potential benefits of this sensor to monitor mutans streptococci activity in saliva.

Determination of bacterial activity by use of an evanescent-wave fiber-optic sensor.

A novel technique based on fiber-optic evanescent-wave spectroscopy is proposed for the detection of bacterial activity in human saliva. The sensor determines th e specific concentration of Streptococcus mutans in saliva, which is a major causative factor in dental caries. In this design, one prepares the fiber-optic bacterial sensor by replacing a portion of the cladding region of a multimode fiber with a dye-encapsulated xerogel, using the solgel technique. The exponential decay of the evanescent wave at the core-cladding interface of a multimode fiber is utilized for the determination of bacterial activity in saliva. The acidogenic profile of Streptococcus mutans is estimated by use of evanescent-waveabsorption spectra at various levels of bacterial activity.

Study of water diffusion in polyacrylonitrile using IR fiber optic evanescent wave spectroscopy

AbstractThis work presents a new approach to the investigation of mass transport processes in polymers. The coefficient of water diffusion in polyacrilonitrile was measured using fiber optic evanescent wave spectroscopy (FEWS). Unclad AgClBr fibers of 0.9 mm diameter were dip‐coated by PAN layers of 1–10 µm thickness. The transmission of the fibers in the mid‐IR was measured using a Fourier transform infrared (FTIR) spectrometer. The penetration of water into these layers gave rise to significant changes in the measured spectrum. These changes were used for diffusion studies in situ. The novel statistical approach to the analysis of spectra was developed for the purpose of calculating the diffusion coefficient, D, using spectral data. This analysis reveals the specific wavelengths which have been taken into account for the calculation of D. The FEWS procedure, combined with statistical treatment of the spectral data, offers a high accuracy in the calculation of parameters of diffusion. It must be emphasized that the cylindrical symmetry of our fibers renders them especially suitable for the diffusion study and allows us to obviate the difficulties caused by end effects. Copyright © 2003 John Wiley & Sons, Ltd.

Blood diagnostics using fiberoptic evanescent wave spectroscopy and neural networks analysis

A spectral analysis of human blood serum was undertaken by fiberoptic evanescent wave spectroscopy (FEWS) using a Fourier transform infrared (FTIR) spectrometer. The blood serum samples were introduced into a special cell designed for FEWS of liquids, with an IR transmitting silver halide fiber as the sensing element. The spectra were analyzed by models of neural networks (NN), and the concentrations of protein, cholesterol and uric acid in human blood serum were obtained. Our results are in agreement with those obtained by ordinary chemical enzymatic methods and multivariate calibration methods. The estimated prediction errors obtained (in percent of the average value) were 4.7% for total protein, 22% for cholesterol and 35% for uric acid. This method can be used for in-situ real-time blood analysis.