Micron and submicron fiber-optic chemical and biochemical sensors have been developed recently in our laboratory. Here we give a theoretical discussion, based on pragmatic modes of operation, of the advantages and disadvantages of optode miniaturization. In most instances we present explicit functional dependences of specific optode characteristics on the optode radius (r). For instance, the absolute detection limit decreases with r³ (good the response time reduces with r² (good noise ratio decreases with r (bad our standard working conditions. Other features that improve with down-sizing include sample volume, sensitivity, invasiveness, spatial resolution, enzyme activity, heating of sensor and/or sample, toxicity and materials cost. Features that may worsen include fluorophore leaching and photodamage to sensor and/or sample. Methods for overcoming these disadvantages make use of the shorter response times of small optodes and forward optical signal collection with small samples (utilizing standard lab microscopes). We refer to the ultimate goal of non-destructive single molecule detection and imaging.

We have developed scanning near-field optical/atomic force microscopy (SNOM/AFM). The SNOM/AFM uses a bent optical fiber simultaneously as a dynamic force AFM cantilever and a SNOM probe. Resonant frequency of the optical fiber cantilever is 15 - 40 kHz. Optical resolution of the SNOM/AFM images shows less than 50 nm. The SNOM/AFM system contains photon counting system and polychrometer/ICCD system to observe fluorescence image and spectrograph of micro areas, respectively. A SNOM-AFM system was newly applied to analyses of biological samples. In this system a feedback signal from AFM in the noncontact mode was used to scan the probe tip along the surface contour of the sample. An optical fiber with a sharp tip on one end was bent for use as cantilever, and ac amplitude of the cantilever deflection was held constant during scanning by moving the stage. Green fluorescent protein (GFP) absorbs blue light and emits green light. GFP should be a convenient indicator of transformation and one that could allow cells to be separated with fluorescence-activated cell sorting. The gene coding to GFP was cloned in recombinant E.coli and plant cells. Spatial distribution of GFP gene expression was clarified using a SNOM-AFM system. Fluorescent spectroscopic analyses supported GFP was surely produced in E.coli and plant cells. Applications to gene identification in human genomes were also discussed.

Previous work has discovered that the silanization of material onto a tapered single mode fiber can form a new effective waveguide that is optimized for capture of fluorescent energy. Such a system actually generates fluorescent energy captured into a fluorescent mode. The adiabatic nature of the taper allows this energy to be efficiently coupled into the fiber fundamental mode, and propagated to the detector end of the sensor. Approaches to determine the optimal design of the tapered fiber loop are considered, both from a fabrication standpoint and theoretical analyses.

Infrared TeX fibers operating in a wide wavelength region have various potential uses in the short distance area such as laser power delivery, remote temperature monitoring and chemical analysis. TeX glass fibers with a minimum attenuation of 0.5 dB/m in the 7 - 10 micrometer range have been obtained. A plastic coating protects these fibers from external environment and improves their mechanical properties. Remote spectroscopy using mono-index fiber is one of the most promising applications. This new technology allows the identification and in situ analysis of many substances such as oils and fertilizers, which have their fingerprint in the 2 - 13 micrometer domain. The detection efficiency using evanescent wave absorption has been studied as a function of the fiber's diameter. It is found that the sensitivity increases very rapidly when the fibers' diameter decreases. The possibility of detecting very low concentrations has been tested by using TeX tapered fibers.

We report the development of a tubular infrared waveguide sensor incorporating a functionalized self-assembled monolayer (SAM) on its metallized interior surface. The SAM used in this application was 11-mercaptoundecanoic acid (MUA) assembled from a 5-mM solution in ethanol onto the inner surfaces of silvered Pyrex_R glass tubing (4-mm inside diameter by 21-cm length). The sensor was adapted with minor modifications to fit standard fiber-launching and detection optics, which incorporate a remote cryogenic detector and mate to a Fourier transform infrared (FTIR) spectrophotometer. The f1.5 optics allow a sufficient number of multiple reflections inside the sensor to achieve spectroscopic sensitivity to the SAM within a 15 minute measurement time at 2 cm^-1 resolution. The overall optical configuration is similar to that of the waveguides used for gas chromatography (GC)-FTIR spectroscopy, except that the inner surface of the sensor, rather than the gas contained in the GC-FTIR waveguide, is sampled. After the FTIR spectrum of a freshly prepared sensor is recorded, the inner surface (functionalized with carboxylic acid) is exposed to an ambient or flowing atmosphere. The terminal acid groups exposed at the surface of the MUA SAM react with basic pollutants, such as amines, which can be indoor air pollutants. The spectrum of the exposed sensor is then recorded and ratioed to the original sensor spectrum to produce an absorbance spectrum characteristic of the reacted, surface-bound pollutant. Our sensor exhibited sensitivity to 15 ppm of octylamine in an ambient atmosphere after 2 hours of exposure at 36 degrees Celsius.

Most intrinsic fiberoptic sensors are based on the evanescent-wave scheme, where the evanescent field of modes guided in a fiber reaches out into a chemically sensitive coating. In the commonly used multimode waveguides, the evanescent field contains only a small part of the total energy, however, thus making evanescent-wave sensors rather insensitive. Combining a transparent substrate and a transparent sensing layer of rather similar refractive index into a common waveguiding structure produces an inhomogeneous waveguide, where a large portion of the total energy transverses the sensing layer. This yields much superior sensor performance. The transmission through a waveguide is subject to various disturbing influences. Thus it is advantageous to combine the inhomogeneous waveguiding approach with a measuring scheme that is not prone to those disturbances. Such a scheme is available with fluorescence lifetime-based sensors. The fluorescence lifetime of an indicator incorporated into the sensing layer is changed by the presence of the respective analyte. This lifetime is independent of the transmission through the waveguide. Thus inhomogeneous waveguiding together with fluorescence lifetime measurement paves the way for optical chemical sensors with high analyte sensitivity and immunity to external disturbances.

Fiber Bragg grating sensors can be used to measure the refractive index of fluids by etching the surface of a D- shaped fiber to expose the evanescent field to the superstrate layer. The cladding is modified and the modal propagation constants are changed thereby shifting the Bragg wavelength of a grating in the etched region. Experiments are reported with etched e-core D-fiber that demonstrate the effect. The Bragg lines of both the fast and slow eigenmodes are blue-shifted when the silica cladding layer is removed and replaced with water or methanol films. Changes in the fiber birefringence are also observed because the perpendicular and parallel modes decay into the cladding at different rates. By using a tunable laser, such as an ECL, with a narrow band Bragg grating filter or three-grating Fabry-Perot interferometer, it may be possible to resolve refractive index variations of 5 by 10^-6. Temperature compensation methods are also discussed including the use of an isolated reference grating and the simultaneous combination of birefringence and Bragg line wavelength shift measurements.

We have demonstrated an evanescent field refractive index fiber sensor comprising a 42 mm Bragg grating in an etched fiber together with a tunable DBR laser. Characterization of different aqueous sucrose solutions resulted in a resolution of roughly 10 mM sucrose. The sensor in the presented form has a theoretical sensitivity of higher than 10^-5 refractive index units (riu) in a refractive index region close to the cladding index of the fiber. However, the technique allows for an even higher sensitivity than 10^-6 riu with a proper signal processing scheme.

Initial results of experimental studies of light propagation by optical fibers with liquid crystalline cores under hydrostatic pressure conditions are reported. Specially drawn hollow-core fibers (capillary tubes of radii 15 microns) were filled with a liquid crystal mixture. The whole system composed of the fiber and the liquid crystal has been placed in a high pressure chamber designed to sustain pressures up to 100 MPa. The liquid crystalline-core optical fiber acts as an optically anisotropic medium characterized by an index ellipsoid, and can serve as a fiber with easily controlled birefringence. Since hydrostatic pressure generate stress effects occurring in the system, a new class of fiber-optic pressure sensors can be introduced. The paper presents preliminary characteristics of the pressure sensor utilizing liquid crystalline-core fibers. Envisaged areas of applications include pipe-lines, mining instrumentation, process control, and environmental protection.

The use of integrated optic chemical sensors in environmental monitoring and remediation applications offers many advantages, the most prominent being that they can easily accommodate multiple sensing-elements, are miniaturized, lightweight, and immune to electromagnetic interference. We are developing versatile, multi-analyte, micro-miniaturized integrated optic chemical sensor (IOCS) technologies for use in closed-loop control and process monitoring for industrial and environmental applications. We have demonstrated a complete integrated optic sensor system and tested it by simultaneously identifying and quantifying samples containing traces of metal ions in a water stream. Conversion of the optical information into control signals is accomplished by a wavelength-division multiplexed optoelectronic unit, which can be remotely located, connected via optical fibers. The simplicity of this process makes this a very promising approach for the fabrication of commercially viable integrated optic devices.

Fluorescence decay of the well-known fluorophore, ruthenium (II) 4,7-diphenyl-1,10-phenanthroline perchlorate, has been studied in a series of sol-gel matrices, including non-polar methyltrimethoxysilane (MTMS) and highly polar tetraethylorthosilicate (TEOS)-based gels. Systematic changes in composition and processing techniques have been fabricated to examine the structural properties of sol-gel silicates for possible oxygen sensor supports. Measurements were performed using both brush-coated and spin-coated sol- gel thin films as well as sol-gel monoliths. Gel compositions consisted of either 100% MTMS, 100% TEOS, or a 1:1 molar ratio of MTMS to TEOS. Quenching behavior was analyzed as a function of varying sol-gel composition, processing technique (spin-coated, brush-coated, etc.), and fluorophore concentration. The use of modeling techniques were employed to enable determination of possible singe or multi-exponential decay behavior in different sol-gel samples. Causes for the variations in quenching properties as a function of gel composition and processing technique were explained by a two-domain model. In addition, phase fluorimetric analysis was conducted on all doped sol-gel samples to determine the change in phase between the quenched and unquenched states of the films. Direct experimental phase data was compared to phase results calculated from the experimental lifetime data in order to examine the accuracy of the luminescence decay times. Possible design of sol-gel supports for oxygen sensors was also discussed.

This paper details the absorption and fluorescence spectra of sodium fluorescein in aqueous solution and sol-gel thin films as a function of pH. Our results show that the fluorescence spectrum is dependent not only on the microenvironment surrounding the fluorophore but also the concentration the probe in the sol-gel matrix. The pH sensitive range is also shown to be a function of the emission wavelength.

Two fiber optic oxygen sensor designs were demonstrated by sol-gel coatings doped with an organo-metallic complex, ruthenium (II) tris-4,7-diphenyl-1,10-phenanthroline. The first design implemented a porous optical fiber coated with sol-gel that showed high sensitivity (less than 1 ppm) towards oxygen gas and a dynamic range up to 1% oxygen. The second optical sensor was based on a collimator device which involved a sol-gel film that was spin coated onto a silica glass disk. Compared to the porous fiber approach, a faster response time and lower oxygen gas sensitivity were determined for this sensor configuration. According the lifetime decay behavior of a sol-gel spin coating, the luminescence decay of the ruthenium complex followed a single exponential decay in nitrogen and air. Also, the spin coated sample showed a greater degree of quenching according to the Stern-Volmer ratio, at greater oxygen concentrations than the ratio calculated for the monolithic film. Analysis of the lifetime decay behavior of the different forming methods revealed that the micro-structure of the gel was dependent upon the type of sol-gel deposition. In this case, spin coated gels resulted in a denser coating than the monolithic film. As a result, these differences in the sol- gel micro-structure were used to discuss the different behavior of the collimator sensor with respect to the porous fiber oxygen sensor.

Difficulties facing optical chemical sensors commercialization and possibilities of overcoming them are discussed.

In the past decade a broad range of sensing applications have been reported utilizing optical-fiber-based sensors. These applications range from the measurement of a variety of physical parameters to the quantitative determination of chemical and biochemical species. The acceptance of many of these sensors by the process monitoring and control industry has not met manufacturer's expectations. This paper describes the special requirements and concerns which must be addressed in implementing fiber-optic sensors in process environments. Topics include sensor specificity and interferences, environmental constraints, long term stability, sensor calibration methods, sensing mechanisms, sensor system design for self-calibration, and performance characterization in process environments. Special requirements for single point and distributed fiber-optic sensing applications including temperature, pressure, strain, humidity, and chemical concentration are described. Methods are discussed for designing robust fiber-optic sensors which remain calibrated for extended periods of time. Also included is a discussion of self calibration methods for use in reflective mode intensity, analyte and distributed based fiber-optic sensors.

A fiber optic based optical low coherence reflectometer has been investigated for process monitoring applications that include its use with both transparent and highly scattering materials. This paper addresses instrumental issues and several applications including measurement of multiple layer polymer films, paint clear coat thickness and refractive index, highly scattering paint layer thickness, and particle size analysis in liquid suspensions.

Federal regulations require companies to monitor leaks from valves, flanges, and pipes (fugitive emissions) in industrial plants on a regular basis. Honeywell has been conducting research into the use of fiber optic sensors for this purpose. The result ia a low-cost chemical dosimeter that is able to detect a variety of fugitive emissions, including various volatile organic compounds (VOCs) down to a few hundred parts per million (ppm). This sensor uses a fluorescent dye that exhibits spectral shifts when its chemical environment is changed. Greater stability is achieved because a spectral change is monitored and the sensor is not dependent on a single relative intensity measurement. Dyes are integrated into an optically clear polymer and immobilized on the tip of an optical fiber. When an analyte permeates into the polymer, a chemical interaction takes place that changes the dye's environment and therefore its spectral fluorescence. With most chemicals of interest, this is a reversible effect. Using a 'smart signal processor' (SSP), a real-time analysis can be made at a distant location. This paper discusses the details and results of a fiber optic sensor incorporating these concepts.

The curing of epoxy adjacent an embedded silica fiber has been monitored in situ by evanescent wave spectroscopy. The epoxy studied is partially fluorinated and has a lower refractive index than the silica optical fiber. This lower refractive index allows the silica optical fiber to be used as a waveguide for the internal reflection of near-infrared light. The curing agent was polyoxypropylenediamine. The epoxy curing was monitored as a function of time by analysis of the near-infrared spectra of the epoxy/curing agent adjacent the fiber. The results obtained from the examination of the near-infrared spectra, particularly the disappearance of the primary N-H stretching/bending combination band at approximately 4935 cm^-1 and the accompanying increase of the C-N overtone band at approximately 4650 cm^-1, showed that the epoxy curing reaction could be followed in real time using an 85 micron diameter silica optical fiber bundle. It was found that the primary amine groups are essentially completely reacted after 60 minutes.

We report on the development of a compact, portable fluorescence lifetime instrument based on phase resolved fluorescence spectroscopy (PRFS). The PRFS biosensor has been designed for detection and discrimination of individual pathogenic bacteria in a biological mixture. The light source can be modulated from 10 - 200 MHz and fluorescence emission is measured by a miniature photomultiplier tube after passing through a compact spectrometer. We have successfully extracted and measured the existence of a mixture of three far-red fluorescent dyes which have similar or overlapping spectral signatures. Data are presented demonstrating the instrument's ability to separate individual fluorophores from a complex mixture using a specially designed chemometric extraction algorithm. This instrument was designed for the possible direct detection and discrimination of the intrinsic fluorescence of biological warfare agents.

A pH sensor based upon spectrophotometric techniques has been developed for in-situ analysis of surface seawater. This sensor utilizes a spectrophotometric pH indicator (Thymol Blue) which has been calibrated for use in seawater as a function of temperature and salinity. Shipboard spectrophotometric pH analyses routinely demonstrate a precision on the order of plus or minus 0.0004 pH units. In- situ analysis of seawater pH has demonstrated a precision on the order of plus or minus 0.001 and an accuracy, using shipboard measurements as a standard, on the order of plus or minus 0.01. The sensor is a self-contained system which pumps seawater, meters in indicator, spectrophotometrically determines indicator absorbance and stores data with a 1 Hz acquisition frequency. The sensor employs two absorbance cells, each with three wavelength channels, to obtain the spectrophotometric absorbance. The sensor system, rated for depths up to 500 m, provides pH, conductivity, temperature and can be operated via computer or in a standalone mode with internal data storage. The sensor utilizes less than 12 watts of power and is packaged in a 29' long by 4.5' diameter aluminum housing.

The theory and design of a new planar surface plasmon resonance probe are presented. The new sensor is based on a folded light pipe combined with a telecentric lens. The inexpensive sensing elements are constructed from pieces of microscope slide and are easy to manufacture. A prototype probe design capable of measuring 2 samples simultaneously was constructed. This is the first SPR probe capable of multiplexing and first order sensing. Initial experimental refractive index testing for 0% to 41% by weight glucose solutions exhibited a sensitivity of 3 by 10^-5 index of refraction units.

In the past, spectroscopic applications with fiber optics have been restricted to the wavelength range above 230 nm, because standard silica fibers with an undoped core and fluorine doped cladding are frequently damaged by exposure to UV-light, especially below 230 nm so quickly that stable UV-light transmission is impossible. Work on a fiber-optic sensor for water monitoring is presented here using an absorption cell and first solarization-reduced fiber samples for light-transportation: the main UV-band around 210 nm shows an induced loss of less than 0.3 dB/m. In this case it was possible to have the full output spectrum of a deuterium lamp at fiber endface, stable over time. Therefore, an optimized UV-lamp-fiber system, including commercially available components, has been developed and is reviewed in terms of performance in the wavelength region around 200 nm, in respect of an effective sensor approach for water a monitoring. In the following step, modification of the deuterium-lamp optics for optimized light coupling becomes more important, in order to maximize the optical power budget for this wavelength-region.

Laser induced breakdown spectroscopy (LIBS) is being used to detect heavy metal concentrations in soils. The overall goal of this effort is to develop a field deployable system that will conduct heavy metal subsurface mapping of the vadose zone using a cone penetrometer deployed fiber optic sensor. This paper presents results on the LIBS analysis of different spiked soil samples with the same chemical matrix, NIST soil samples with variable matrices, a comparison of the performance of the LIBS system with free space delivery of the laser beam versus the performance using an optical fiber probe, and the effect of several system parameters on performance.

The aim of the described research is to develop a general system for characterizing and developing signal transduction systems for microbiosensors. The approach that we are using is applicable to signal transduction systems based on surface plasmon resonance, chemiluminescence, fluorescence, mass as well as other phenomena. The specific goal of our approach is to develop a general system that will allow for the systematic characterization of the effects of the affinity of the sensor specificity element for the target analyte, the effect of analyte mass on signal size and the general performance of the sensor system with respect to sensitivity and selectivity. At the same, time this system should allow for the characterization of the distribution of biospecificity elements on the sensor surface. We chose the anti-fluorescein monoclonal antibody approach for this development system, since the antigen fluorescein can be attached to many different molecules and organisms through free amine groups via reaction with fluorescein isothiocyanate. Also, well characterized monoclonal antibodies with a broad range of Kd values are available. We also describe rapid procedures for generating proteins for use in biosensor applications.

The production of a variable array of optical point sources from a single point source can be achieved through the self- imaging properties inherent in a rectangular waveguide. Two prototype devices, based upon this concept, were designed and constructed. The resulting output patterns are discussed along with future design considerations and applications.

Specific detection of extremely low amounts of antigens or disease markers allowing the diagnosis of diseases and infections at a very early stage has become a major driving force for the development of new generations of biochemical sensors. To match this goal, we propose the substitution of the widely used fiber-shaped evanescent field sensors by planar single-mode metal oxide waveguides. In combination with bioaffinity assays, this transducer geometry offers benefits such as enhanced sensitivity, ease of sensor handling and preparation, sample volume reduction, versatility, and low cost per test. Recently, planar waveguides have been used in sensor schemes exploiting the changes of the so-called effective refractive index (caused by changes in mass of surface-bound biomolecules): grating couplers, surface plasmon resonance, and interferometers. However, compared to luminescence-based sensor schemes, the sensitivities of these label-free methods are inferior. In this paper we report on a new generation of luminescence- based bioaffinity sensors for human diagnostics including optimization of the planar evanescent field transducers, the design of a compact sensor system, and a first study of the binding of fluorophore-labeled IgG to protein A immobilized on the transducer.

The five year survival rate after stereotactic removal of deep-seated malignant brain tumors is virtually 100% mortality. Specific problems in treatment include: (1) Lesions often present late and are of large size. (2) Position -- lesion overlies vital structures. So surgical/radiotherapy lesion destruction can damage vital brainstem functions. (3) Difficulty in differentiating normal brain from malignant lesions due to poor deep visibility and similarity of brain tissues. This study aimed to use the unique properties of the laser: (1) to minimize damage during surgical removal of deep-seated brain lesions by operating via fine optic fibers; and (2) to employ the propensity of certain lasers for absorption of (nontoxic) dyes and induction of fluorescence in particular brain substances for more complete tumor removal. The results of the technique, developed here, were found to minimize thermal damage and to accurately differentiate tumor from surrounding normal brain.

The authors are developing a family of distributed fiber optic sensors (DIFOS) for use in prevention and monitoring of corrosion in advanced structural components of aging aircraft. These sensors, based on optical fibers that are intrinsically sensitive to either water or changes in pH, will alert maintenance personnel to the presence of water in aircraft lap joint structures and other inaccessible critical areas. We have demonstrated that the distributed fiber optic moisture and pH sensors can detect and localize water and/or changes in the pH environment surrounding the fiber sensor with 10-cm spatial resolution. A dual- wavelength (850 nm and 1300 nm) optical time domain reflectometer (OTDR) was used to characterize the spatial sensitivity and resolution of 20-meter lengths of both the moisture-sensitive and pH-sensitive optical fibers. The results of the characterization efforts demonstrated conclusively the ability of these distributed sensors to detect and localize their respective target measurands within 10 cm, with built-in 'self-referencing' to distinguish between moisture (or pH changes) and spurious effect (e.g., fiber bending).

A truly distributed sensing system for nonpolar organic chemicals has been built up by adapting a chemically sensitive polymer-clad silica fiber to an optical time domain reflectometry (OTDR) set-up. This arrangement allows to measure the time delay between a short light pulse entering the fiber and the discrete signals of backscattered light caused by chemical effects in the fiber cladding. The backscatter signals originate from changes in the light guiding properties of the fiber, which are affected by the enrichment of chemicals in the cladding through the evanescent wave. The shape and magnitude of signals caused by penetrating chemicals either due to changes in refractive index, or absorption and fluorescence properties of the fiber cladding, have been examined. Changes in the optical properties of the cladding were produced either by contacting the fiber with solvents (e.g. tetrachloroethane) or organic dyes such as methylene blue and rhodamine 800. Typical parameters, that influence the intensity of the OTDR response signal are the refractive index, concentration and molar absorptivity of the analyte, as well as the power of the light source.

The concept of fully- or quasi-distributed chemical sensing using OTDR techniques has attracted much research interest. Much of the work to date in this area has employed large core non-telecom grade optical fiber. Typically, this has been PCS fiber from which the cladding has been removed and replaced with sections of doped polymers. Evanescent wave interactions between the guided light and the coatings provided the sensor modulation. In this paper we report the use of telecom-grade optical fibers to which analyte- sensitive reagents are attached via a novel configuration at the fiber tip. This approach enables the use of low attenuation fibers, good quality directional couplers and direct, as opposed to evanescent wave, interactions. In order to exploit fully the low attenuation and commercially available OTDR units, it is necessary to operate at one of the telecom windows, usually 850 nm. This requires the use of appropriate NIR dyes. We report some initial results for pH sensing using this approach. We also present results for O₂ single point sensing using blue-excited fluorescence and comment on factors concerning the use of fluorescence quenching in distributed systems.

Surface contamination of insulators in high voltage transmission and distribution systems may lead to troublesome flashovers which interrupt service. Insulator contamination may be monitored using direct measurement of equivalent salt deposit density (ESDD), which directly relates to the flashover voltage. A fiber-optic evanescent- coupling fiber-optic ESDD monitor is presented. The use of a piece of D-shape E-core fiber as sensor head can provide a sensitive and large area ESDD monitoring system. We have demonstrated the use of D-shape fiber in monitoring ESDD on insulator surfaces. A simple process has been developed to precisely etch the D-fiber. The polarimetric and evanescent loss sensors have been investigated. The evanescent loss sensor is particularly suitable for in-situ ESDD monitoring in power transmission lines and substations.

A novel separations-based fiberoptic sensor (SBFOS) is described for remote analysis that incorporates capillary electrophoresis (CE). High sensitivity is possible with laser induced fluorescence detection and a unique and powerful element of selectivity is afforded by the exceptional separation power of CE. Speed of analysis and the possibility of remote control are further attributes which render the system useful for sensing applications. Details are given in this report for a SBFOS that employs a single-fiber optical configuration and a single buffer reservoir CE arrangement. The fiberoptic probes the outlet of a short separation capillary in a simple frontal mode of operation. Design considerations and the results of preliminary evaluations of the separation and detection characteristics of the SBFOS are presented.

The properties and performances of the thermal lens detector, based on a double beam absorption scheme, were studied in a capillary electrophoresis system with different types of pollutants, e.g. pesticides. The setup of the detector system is miniaturized using smallest deflection pathlengths between the cell and the pinhole (5 mm). The probe laser beam (HeNe laser, 633 nm) and the excitation beam (Ar⁺ ion laser, 364 nm, 457 nm, 488 nm, 514 nm) with a crossed setup are directed by mirrors into two microscope objectives, which focused the beam to a 15 micrometer waist inside the capillary. The detection volume is in the range of 75 n1 using a 75 micrometer capillary. The change of the intensity of the probe beam is detected behind a pinhole with a photodiode, which is protected with different band pass interference filters. The excitation laser can be used in the multiline order. Different types of hydrodynamic and electrokinetic probe injections are compared to optimize the probe volume. Micellar electrokinetic methods are used for separation of pesticides. The performance of the detector in capillary electrophoresis was assessed by different types of capillaries and compared with a conventional absorption detector. The limit of detection is at least one order of magnitude better than the absorption detector.

The operation of an efficient cw thulium-doped fiber laser emitting at wavelength, lambda equals 2.31 micrometer is reported. The operation of the fiber laser is optimized with a view to producing a small and efficient laser source for optical absorption based gas sensing. A 2 mW output power combined with a high slope efficiency make this fiber laser a useful source for sensing spectroscopic based hydrocarbon gases which absorb at lambda equals 2.3 micrometer. A lower limit of detection of 1000 ppm meters for methane is routinely demonstrated using an unoptimized laser system. The tunability of the fiber laser has also been investigated in order to target specific hydrocarbon absorption features.

The response of state of the art anion optodes often cannot be described in a thermodynamically exact manner because the ionic strength within the membrane phase of such optodes changes during the course of a titration. Incorporating lipophilic charge sites in the anion optode membranes provides a constant ionic strength in the membrane phase, the ability to measure anion activities, and a more thermodynamically describable system. This configuration has been used to create a micrometer-sized nitrite-selective optode. Recent elucidation of the many biological roles of nitric oxide (NO) has spurred interest in sensitive and selective detection of this molecule. In biological systems NO is converted to NO₂^- within 30 sec and the biological concentration of NO₂^- is normally on the micromolar level. The optode we have prepared contains a selective vitamin B₁₂ derivative ionophore, a fluorescent chromoionophore (ETH 2439 or ETH 5350), and lipophilic charge sites. These components are entrapped in a highly plasticized PVC matrix which is placed on the distal end of the fiber. Sensor characteristics such as limit of detection and reversibility are presented.

The amount of dissolved hydrogen sulfide is an important parameter in many environmental applications. Conventional methods for H₂S detection depend on iodometric titration or spectroscopic measurements. Unfortunately these methods are not applicable for direct measurements in natural systems. A recently described method for the on-line detection of H₂S is based on quenching of fluorescence of thioneine. The reaction between H₂S and thioneine was described as reversible photo-reduction. This reaction was tested in order to design an optical microsensor for the measurement of H₂S in sediments and other biological systems. We immobilized thioneine in several matrices and investigated these materials with respect to response time, mechanical stability, the influence of the excitation light and the reversibility. The sensing materials were deposited on the tip of optical fibers. The measuring system for the excitation and detection of the fluorescence consisted of a yellow light emitting diode, a fiber-optic coupler and a photomultiplier. The excitation light was intensity modulated to enable measurements in ambient light. Our results indicate that the thioneine based reaction scheme for H₂S detection is not very suitable for use in a H₂S optode due to lack of reversibility, long response times, and the need for regeneration of the sensor chemistry.

The development of a novel Teflon-coated optical fiber sensor for chlorinated organic determination and a PVC- coated sensor for pesticide determination is described. Current analytical techniques for these compounds in water are not suited to in-situ or on-site measurements. As a result, straight-forward techniques that feature a short analysis time, sufficient selectivity and adequate sensitivity are in high demand. An infrared fiber optic sensor which operates in the 4 to 16 micrometer wavelength region has been developed for the in-situ monitoring of chlorinated hydrocarbons and pesticides in water. The sensing element consists of a silver halide (AgCl_xBr_{1- x}) optical fiber, coated with Teflon or poly (vinyl chloride) (PVC) which enriches the analyte in the evanescent wave region of the fiber. Enrichment of the analytes occurs in the minute range and is reversible. Using trichloroethylene (TCE) and alachlor as representative pollutants, evanescent wave spectrometry in the mid-infrared (MIR) region is shown to provide good performance down to single ppm levels. Absorbance data were recorded at 938 cm^-1 and 1104 cm^-1 for TCE and alachlor respectively. Furthermore, it is shown that the technique can be applied to multi-analyte samples.

A procedure has been developed for the separation, preconcentration and fiber optic analysis of DDT residues in soil and soil water. Solid phase extraction was achieved by polymer adsorbent columns, and the DDT fluorescence signal was compared to a stock working solution (25 (mu) M) of soiled tap water. The XAD-4 elluent was found to possess the highest DDT signal in relation to other adsorbents investigated. The method proved sensitive to analyze concentrations down to 1.2 (mu) M (approximately 400 (mu) g/L) and can be performed within 3 minutes of obtaining a soil sample. With this in mind we envisage the online application of such a procedure for the in-situ analysis of DDT residual values.

A procedure has been developed for the measurement of ammonia in water. The paper describes the effect of the ammonia concentration on the emission of a fluorescent dye. From a plot of change in fluorescence against ammonia concentration, a linear response is achieved up to 250 ppb, with a detection limit of 8 ppb. When subjected to a solution of 50 ppb NH₃, the device showed 90% recovery of the original signal, within approximately 6 sec. The immobilized form of the fluorophore ensures an interaction with only molecular ammonia (NH₃) rather than ammonium ions. Hence the fiber-optic device based on the method reported here is insensitive to pH effects.

A new method for the measurement of pesticide residues is described that utilizes an excited state photo-reaction in conjunction with a dehydrogenase enzyme based enzymatic reaction. The presence of the pesticide inhibits the enzymatic reaction, thereby affecting the production of the NADH. The latter co-factor undergoes an excited state photo- reduction, resulting in the NAD⁺ and photo-reduced form of the indicator fluorophore. The reported method is suitable for analyzing a number of pesticides, selectively. Various advantages, including the possibilities of using the assay in complex matrices, non-separation formats and cost- effectiveness, are discussed.

A sensor for the measurement of volatile aliphatic chlorocarbons is reported based on quenching of a fluorescent indicator. Chlorocarbon vapors when in contact with the fluorescent indicator immobilized in a polymer film cause a quantitative decrease in the fluorescence intensity. The quenching is rapid and reversible for a range of chlorocarbons investigated, including carbon tetrachloride, trichloroethylene, perchloroethylene, chloroform and 1,1,1- trichloroethane. Quenching constants for the sensor ranged from 700 M^-1 (trichloroethylene) to 8500 M^-1 (perchloroethylene) allowing detection limits of 28 (mu) M (660 ppm v/v) and 2.4 (mu) M (56 ppm v/v) respectively. The sensor offers response time of ca. 100 s and recovery times, governed by diffusion of the analyte in the polymer film, are less than 100 s.

An optical sensor for carbon tetrachloride measurement has been developed that utilizes a covalently bound fluorescent indicator. In methanol solution the quenching of the indicator by CCl₄ followed Stern-Volmer kinetics (k_q equals 9.9 multiplied by 10⁹ M^-1s^-1), suggesting a diffusion-controlled process. Solutions we also quenched by other chlorocarbon compounds, e.g. perchloroethylene. Once immobilized, the indicator behavior coupled with the preferential adsorption of CCl₄ by the porous substrate offered selective measurement of carbon tetrachloride. The sensitivity of the sensor varied with concentration according the the adsorption isotherm, with a linear Stern-Volmer plot (K_sv equals 1000 M^-1) up to an analyte concentration of 100 (mu) M (2400 ppm v/v). The sensor offers a detection limit of 20 (mu) M (480 ppm v/v), the equivalent of a 3.0 (mu) M (460 ppb v/v) aqueous solution headspace. A sensor for fiberoptic based monitoring of carbon tetrachloride is discussed.

Improvement of the optical fiber oxygen sensor based on the fluorescence quenching by oxygen gas was studied. Using the newly synthesized poly-l-methylmethacrylate (PMtMA) and its blend of the PMtMA/PMP as the cladding layer, in which sensing dye was doped, the plastic optical fiber (POF) O₂ sensor with high sensitivity and a fast response time could be realized. In addition this sensor didn't receive any affect by humidity.