A market study is presented, concerning fiber optic biosensors which have been developed in Europe. The main aspects discussed in the study are principal applications, a sketch of the European companies involved in research and production, their success, and future market trends. The key areas in which fiber optic biosensors are highly competitive with conventional devices are pH and blood-gas monitoring and immunoassay. In addition to these leading applications, there is also interest for many applications in monitoring temperature, pressure, and blood flow. Other sensors of interest are more specifically addressed to particular aspects of certain diagnoses or therapies: for example, for monitoring glucose, bile, the light level in tissues, kidney stones, or parameters related to metabolism.

Fiber optic biosensors based on the firefly and the bacterial bioluminescence reactions have been constructed and incorporated in a specially designed flow-cell for the sensitive determination of ATP and NADH, respectively. The bioluminescence enzymes were immobilized on preactivated polyamide membranes which were placed in close contact with the surface on one end of a glass-fiber bundle, the other end being connected to the photomultiplier tube of a luminometer. When using the continuous-flow device with the firefly luciferase or the bacterial system immobilized separately on different membranes, the detection limit for ATP and NADH were 0.25 and 2 pmol, respectively. The versatility of the fiber optic probe has been improved by co-immobilizing the bacterial bioluminescent system and the firefly luciferase on the same support enabling the use of a single sensor for the selective, specific, and alternate determination of these two analytes. Compatible reaction conditions preserving the activity of each co-immobilized enzyme without impairing its stability were found. The selection of the appropriate reaction medium was done using a four port valve. Alternate quantification of ATP and NADH could then be performed in the linear ranges 0.25 pmol - 3 nmol and 5 pmol - 1 nmol, respectively with a RSD of 4.0 - 4.5%.

Langmuir-Blodgett technique is shown to be a suitable method for construction of the functionally-oriented layers of immunoglobulin G (IgG) which bind antigen better than in the case of chemical immobilization of IgG on the same substrate. It is assumed that the fluorescent detection of the conformational changes in the molecule of IgG or in the regular structures of IgG molecules after the interaction with antigen can be used for the development of the new type of immunosensors.

A very compact and easily-transportable optical-fiber sensor for 'in vivo' detection of bile reflux from the duodenum into the stomach (entero-gastric reflux) has been developed. It makes use of two light-emitting diodes (for signal and reference, respectively) and of a special electronic circuit which processes the signals and provides the readout on a display. Quartz and plastic fiber bundles are used and compared in order to obtain the best solution in terms of signal levels and price. A suitable probe was specially designed and made finalized for 'in vivo' measurements. Measurements with the optical sensor were performed on several patients. A comparison with the traditional indirect method of detection, based on a change in acidity inside the stomach, showed the eminently greater suitability of the optical sensor for detection of entero-gastric reflux.

The pH-sensitive fluorescent dye 1,3-dihydroxy-pyrene-6,8-disulfonic acid (DHPDS) was used to measure intracellular pH (pHi) from the surface fluorescence of the isolated perfused rate liver. 1 micrometers of the diacetyl ester of DHPDS was added to the perfusate. The dye readily accumulated in hepatocytes where it was hydrolyzed to form the fluorescent pH indicator. Surface fluorescence was excited by focusing monochromatic light from a spectrofluorometer onto the end of a fiber light guide that illuminated a part of the liver surface. Two excitation wavelengths were used, one where fluorescence intensity was pH sensitive, the other at the isosbestic point. Emitted light was collected by a second fiber optic and returned to the emission side of the spectrometer. A ratio was computed between fluorescence intensities at the pH-sensitive excitation peak wavelength and the isosbestic wavelength, thus yielding measurement insensitive to changes in dye concentration and in excitation light intensity. Intracellular calibration of dye fluorescence was done by clamping pHi to perfusate pH with the use of the cell membrane H+/K+ -ionophore Nigericin. The method was used to monitor changes in pHi caused by addition and removal of NH4Cl. Data obtained in the perfused liver were in good agreement with those reported for isolated liver cells. The technique appears adequate to determine hepatocellular pH in the liver and will allow study of regulatory mechanisms of hepatocyte pHi in the intact organ.

In this paper, a fiber optic liquid crystalline (LC) microsensor for temperature measurement in high magnetic field is presented. The LC layers obtained by dispersion of cholesteric liquid crystals in a polymer matrix are placed at the end of the fiber optic head. A reflectivity of cholesteric LC layers depends on temperature with high sensitivity. Depending on the choice of microcapsulated cholesteric LC dispersed in the polymer matrix, the sensor can detect temperature in a narrow band (about 5 degrees) within the range 20-50 degree(s)C with a sensitivity of up to 0.01 degree in its linear range of operation (up to 1 degree(s)C). In order to increase range of operation we have used four light sources with different wavelengths. Typical multimode optical fibers for transmission of light from the light source (He-Ne, LD, LED) to the LC foil and next, after reflection, to the photodetector have been used. The microsensor probe was placed inside the electromagnet gap in which a magnetic field up to 1.2 T could be reached. As a result the temperature characteristics of the microsensor in different magnetic field configurations are presented. The principal conclusion to be drawn is that the temperature characteristics are not influenced by the magnetic field.

In order to measure the pH-zone with active optodes, the principles and effects of co- immobilization of several dyes are studied. Two techniques are compared: dye binding on poly.N (vinylimidazole) (PVI) grafted on silica fiber; and dye absorption on a cross-linked styrene-divinylbenzen resin at the end of fiber. The possibilities of these techniques with several reagents co-immobilized on the same optode are discussed.

This paper presents a method for optically sensing enantiomers (optical isomers) of biological amines such as norephedrine, and drugs such as the (Beta) -blocker propranolol. It is based on the use of a new lipophilic aromatic ammonium ion carrier (DODD) and a highly fluorescent lipophilic proton carrier (DZ 49) dissolved in a pvc membrane. Recognition of one of the enantiomers is accomplished by specific interaction of the amine with the optically active lipophilic substrate in a pvc membrane. The amine, which is present as an ammonium ion at physiological pH, is carried into the pvc membranes. Simultaneously, a proton is released from the proton carrier (a lipophilic xanthene dye) that thereby undergoes a change in both color and fluorescence intensity. The sensors respond to three analytes in the concentration range from 0.01 to 10 mM for propranolol, 0.3 to 100 mM for norephedrine, and 1 to 100 mM for 1-phenylethylamine. The selectivity coefficients (Kopt) are 0.8, 0.7, and 0.8 for propranolol, norephedrine,a nd 1-phenylethylamine, respectively. It is of potential utility for specifically recognizing one out of several isomers, in particular bioactive amines, where one form usually is active only. The carrier showed stronger affinity for compounds which contain naphthyl rather than phenyl substituents.

Many fiber optic sensors for chemical species rely on a change in the fluorescence characteristics of a dye in response to its chemical environment. Such sensors often require the complex immobilization of the fluorescent species on or near the fiber surface. A novel process, whereby a highly transparent porous glass can act as a support for sensor dyes, is presented. The sol-gel process for low-temperature fabrication of porous glass has been used as a means of entrapping chemically-sensitive dyes for fiber optic sensor applications. As a proof of principle, fluorescein dye was used to investigate the performance of a pH sensor. Because of its potential for distributed sensing and planar integrated optics sensors, evanescent-wave rather than direct excitation of fluorescence was used. A short length of unclad fiber was coated with a thin layer of porous cladding within which the pH-sensitive dye is entrapped. The sensor displayed maximum sensitivity in the range of pH 3.5 to pH 6.5 with a response time of less than 5 seconds. The suitability of the technique for distributed and integrated-optic sensing of gaseous and liquid species is discussed.

Optical sensing techniques can be considered as powerful information sources on the biochemistry of tissue, blood, and physiological fluids. Various sensing modalities can be considered: spectroscopic determination of the fluorescence or optical absorption of the biological medium itself, or more generally, of a reagent in contact with the biological medium. The principle and realization of the optical sensor developed are based on the use of polished fibers: the cladding of a monomode fiber is removed on a longitudinal section. The device can then be inserted into an hypodermic needle for in-vivo measurements. Using this minute probe, local measurements of the tissue biochemistry or metabolic processes can be obtained. The sensing mechanism is based on the propagation of the evanescent wave in the tissues or reagent: the proximity of the fiber core allows the penetration of the model field tail into the sensed medium, with a uniquely defined field distribution. Single or multi-wavelength analysis of the light collected into the fiber yields the biochemical information. Here an example of this sensing technology is discussed. In-vitro measurement of bilirubin in gastric juice demonstrates that the evanescent wave optical sensor provides a sensitivity which matches the physiological concentrations. A device is proposed for in-vivo monitoring of bilirubin concentration in the gastro-oesophageal tract.

With the presented ion-selective optode membranes total ion concentrations of sodium, potassium, and calcium are measured reversibly with the same selectivity as in potentiometric systems. The optically sensing membranes combine the well established neutral carriers together with neutral so-called chromoionophores which change their absorption spectra in the VIS region upon complexation of hydrogen ions in the same membrane phase. Membranes are mounted in an optical flow-through cell with a volume of 300 (mu) l. All measurements are referred to a pair of blank-membranes in a reference cell to compensate for interferences induced by the sample. The response time is in the range of seconds. A good correlation to reference methods is achieved.

A fiber optic polarimeter sensor is presented, which is capable of measuring low concentrations of biological macromolecules. Adsorption processes of two types of antibody- proteins have been measured so far, in a concentration of approximately equals 3X10-7Molar (MWequals150kD), resulting in phase changes of approximately equals 0.25X2(pi) .

An integrated optical sensor for the detection of gases like CO2 and SO2 is described. The working principle is as follows: The gas to be measured is absorbed by a sensitive film, which changes its refractive index with gas absorption. The sensitive film is deposited onto an integrated optical interferometer. As the intensity distribution of waveguide modes is not totally confined to the waveguide, interferometer phase changes with the refractive index of the film. Tests have been made with interferometers of the Fabry-Perot-type. Interferometer phase is measured continuously using the serrodyne detection scheme. Organically modified silicates are used as sensitive films. These glassy films are prepared by the solgel technique, which allows the incorporation of functional organic groups within a network of siloxane bonds. The ability of selective gas absorption of these materials is determined by chosing appropriate functional groups. Films sensitive toward CO2 and SO2 have been fabricated and tested under different gas atmospheres. Temperature dependence of the sensor signal and cross sensitivities toward other gases and humidity have been investigated.

This paper reports on progress on gas sensing using real-time correlation spectroscopy, where a gas is used to 'recognize' its own spectral absorption lines. Our recent results on methane detection using pressure modulation spectrometry are shown, and a new method of modulating the absorption of the gas in the reference cell section of an ammonia detection system is reported for the first time. The basic concept of correlation spectrometry involves the passage of light sequentially through two gas cells, a reference cell containing a known quantity of the gas to be detected, and a sampling cell where the presence of the gas is to be determined. An optical signal passing sequentially through the cells will suffer absorption in each of the cells. If the absorption in the reference cell is periodically modulated, then the total absorption depends on whether the gas absorption lines in the sampling cell correlate with those in the reference cell gas. If the absorption lines of the gases do not correlate strongly, then the modulation index of the optical signal is essentially unaffected by the presence of the different gas in the sampling cell. Therefore, the concentration of a specific gas in the sampling cell can be quantified by this means. Pressure modulation of the gas within the reference cell is achieved by the use of a novel acoustic resonator. This device provides a reasonable pressure ratio while being compact and easily driven. Unlike previous piston-compressors, the high modulation frequency of the resonator improves the tolerance to transients in the optical signal produced by the passage of dust through the optical beam. The system can be tailored to detect a desired gas by changing the reference gas and a broadband section filter. Results for methane are presented in this paper. A novel method for detection of ammonia gas is reported for the first time. This involves Stark modulation of the gas in the reference cell, by the application of an electric field. This method is applicable to gases with strong electric dipole moments, such as NH3, CO, NOx, and HC1.

Optoelectronic light-emitting diode-photodiode pairs based on multicomponent GaInAsSb and InAsSbP solid solutions have been researched and developed. Such pairs are able to detect absorption bands of water and gases belonging to the spectral range 1.8 - 4.8 micrometers (H2O, CO, CO2, H2S, N2O, CH4, etc.). Two-wavelength models of a new type of optical moisture meter and a methane meter was fabricated using the developed LEDs and high-efficiency photodiodes.

Techniques of diffuse reflectance and fluorescence spectroscopy have been utilized for the development of new quantitative methods for the analysis of chlorine. The reflectance method involves the use of a dry reagent chemistry, prepared by immobilizing (sigma) -tolidine on a nylon 66 membrane, which is interrogated by means of optical fibers. Chlorine concentrations in the range 0-5 ppm can be measured with a limit of detection of 0.043 ppm. The fluorescence technique is demonstrated by the measurement of quenching of 9-vinylanthracene by chlorine. Efficient quenching of fluorescence of this dye is observed with a Stern-Volmer constant of 8667 M-7. The findings demonstrate the possibility of developing an analytical method for the determination of chlorine based on fluorescence quenching and optical fibers.

This paper presents a portable, battery operated, instrument for measuring chlorophyll fluorescence on both peaks (685 and 720 nm) simultaneously. The instrument is named LEAFR (Laser Excited Automatic Fluorometer). The fluorescence is excited by a low power HeNe laser through a single optical fiber. The same fiber is also used to collect fluorescence, through a clip on probe. Fluorescence signals are detected by two photomultipliers with wavelengths selected by interference and long pass filters. An internal microprocessor controls the instrument and stores data in permanent RAM, for a later backup on an external PC. The preprocessing software allows real time display of parameters of physiological significance, as the F685/F730 ratio or fluorescence induction kinetics parameters. Some typical applications results are also briefly discussed.

Recent emphasis on compliance with national and EC directions on water quality has created a requirement for real-time in-situ monitoring techniques such as provided by fiber optic sensing technology. Health risks associated with high concentrations of nitrate ion in drinking water demand regular monitoring of this species. Preliminary results from a simple fiber optic sensor for continuous monitoring of NO3- in water are reported. The sensor is based on the absorbance of UV-radiation in the 200nm region. Dual- or multi-wavelength referencing is used to compensate for non-measured related signal losses. Good quality UV- transmitting optical fibers enable remote operation of the device. The sensor performance is linear over the range 0-20 mgN per liter with a resolution better than 1mgN per liter. The sensor is particularly suitable for rapid on-line testing of compliance in the region of the EC guide (5.6 mgN per liter) and maximum (11.3 mgN per liter) levels. Proposed developments of this device are reported.

This paper discusses the requirements for a portable infrared analyzer and presents the design of a four wavelength NIR analyzer utilizing the integrated multichannel detector technique for wavelength separation and detection. This technique, together with an electrically modulated miniature tungsten filament source and surface mount electronics manufacturing, provides a compact, rugged handheld instrument construction without any moving parts. Improved accuracy and short stabilization time is achieved through a combination of thermoelectric temperature stabilization in the four channel detector and a calculated signal compensation for the residual temperature error. Parallel analog phase sensitive detection of the detector signal maximizes the S/N ratio and maintains the simultaneity of the measurement. All composition calculations are performed in a microcomputer built inside the analyzer. The weight of the prototype analyzer is about 1 kg and a NiCd battery pack provides capacity for hundreds of single measurements or about 3 hours of continuous operation. Two prototype instruments have been fabricated with optimized NIR wavelengths for the moisture measurement of milled fuel peat on production fields. The accuracy of digitized two-wavelength signal ratios were tested in the laboratory over time and against temperature. Full accuracy is achieved in 10 seconds after switch-on and the maximum short time peak-to-peak variation in the signal ratios is 0.2%. The errors due to temperature fluctuations in the range from +2 to +50 degree(s)C are between -0.4 to +0.6%. The instruments were calibrated using 102 samples of Finnish milled fuel peat. the cross-validation testing of calibration gave a standard deviation of 1.6% (moisture by weight) compared to the reference method. Other applications for the analyzer are being planned in wood processing and chemical industries as well as in agriculture.

A fiber optic sensor system based on the photothermal effect has been developed and applied to very low concentration measurements in solutions. The sensor head comprises three closely spaced optical fibers for excitation, probe, and reflected probe light. A combination of reflective and refractive miniature optics is used to focus the respective beams into the probe volume. If an absorbing substance is present, the absorbed light power from the modulated excitation beam generates a refractive index gradient in the probe volume, which can be observed via deflection measurements of the non-absorbing cw probe beam. The reflective probe beam signal detected after phase synchronous demodulation is proportional to the substance concentration. Using a monochromatic lightsource with variable wavelength it is possible to discriminate different substances. With this system, we have analyzed Cu-II concentrations in galvanic solutions from 1000 ppm down to concentrations below 1 ppm, thus reaching the sensitivity for waste-water control. Applications for this chemical sensor system are in-line environmental and pollution control of water due to its very high sensitivity. The large dynamic range also makes it suitable for various in-line process control tasks.

An optical sensor for measurement of water in ethanol is presented that is based on a fluorescent solvent polarity probe immobilized on an ion-exchange membrane. The probe responds to changes in solvent polarity of alcohol/water mixtures by both a shift in the fluorescence emission maximum and a change in the fluorescence quantum yield. In this sensor, the analytical information is the relative fluorescence intensity measured at 620 nm (500-nm excitation). The sensor can be applied over the range from pure ethanol to pure water, however, maximum sensitivity is achieved in the range of 80 to 100% ethanol. The response time (t90) is in the order of 15 s. Given the unique applications of fiber optic sensors (e.g., in remote and fire-proof sensing), the new sensor may be applied for quality control of ethanol in distilleries and anhydrous ethanol production.

The development and application of various optical sensors will be presented. Among these are optical sensors (optrodes) with immobilized enzymes, coenzymes, and labeled antibodies. The NADH formation of coenzyme dependent enzymes was used for detection of lactate, pyrovate mannitol, ethanol, and formate. An enzyme optrode based on a pH-optrode as a transducer for the monitoring of urea and penicillin in fermentation media was developed. For preparing an oxygen optrode, oxygen-sensitive fluorophores were entrapped in a gaspermeable silicone matrix that is attached to the distal end of a bifurcated fiber optic waveguide bundle. By labeling of immuncomponent with fluorophores or enzymes, which transpose fluorophores or chromophores, immunreactions were observed by an optical sensors.

In this paper, we describe the design of a fully reversible JR fibre optic chemical sensor for glucose based on the chemical modification of the fibre surface. The chalcogenide glass fibre (composed of As, Se, and Te) used in this experiment as an ATh element belongs to the new class of infrared transmitting glasses. A third of the fibre optic's length (10 cm) was used as an intrinsic sensing element and was successfully derivatized. The quality control of the first chemical process on the uncoated fibre surface, known as the silanization, was performed with Scanning Electron Microscopy, Secondary Ion Mass Spectrometry and Infrared Microscopy. Homogenity of the silane layer (3-APTS) was checked by analysing the silicone peak intensity. The immobilization of the Glucose oxidase (GOD) via glutaralaldehyde and 3-aminopropyltriethoxysilane (3-APTS) was optimized after removing the protective polyamide coating of the fibre surface. This technique led to a stable glucose oxidase film on the fibre surface which was resistant to extensive water rinsing. Glucose solutions were pumped through a flow-through glass cell (ca. 0,5 ml) and continuous in-situ measurements were carried out with the use of an FTIR spectrometer (Bruker IFS-88) providing spectral information in real time. Glucose could be detected in the lower biological range by measuring the absorbance (at 1153 cm1) of the gluconic acid which is produced by the glucose oxidation catalyzed by the enzyme (GOD) covalently bonded to the fibre surface. This work shows the strongly enhanced capability of chemically modified JR-fibre-optics for use as miniaturized biosensors.

The role of modern analytical chemistry is not restricted to quality control and environmental surveillance, but has been extended to process control using on-line analytical techniques. Besides industrial applications, highly specific, ultra-sensitive biochemical analysis becomes increasingly important as a diagnostic tool, both in central clinical laboratories and in the doctor's office. Fiber optic sensor technology can fulfill many of the requirements for both types of applications. As an example, the experimental arrangement of a fiber optic sensor for biochemical affinity assays is presented. The evanescent electromagnetic field, associated with a light ray guided in an optical fiber, is used for the excitation of luminescence labels attached to the biomolecules in solution to be analyzed. Due to the small penetration depth of the evanescent field into the medium, the generation of luminescence is restricted to the close proximity of the fiber, where, e.g., the luminescent analyte molecules combine with their affinity partners, which are immobilized on the fiber. Both cw- and pulsed light excitation can be used in evanescent wave sensor technology, enabling the on-line observation of an affinity assay on a macroscopic time scale (seconds and minutes), as well as on a microscopic, molecular time scale (nanoseconds or microseconds).

Distributed optical-fiber sensing (DOFS) is a technique that utilizes the very special properties of the optical fiber to make simultaneous measurements of both the spatial and temporal behavior of a measurand field. As such, it provides an extra dimension in the measurement process, leading to finer monitoring and control, and to a new level of understanding, especially in regard to the behavior of large structures. Thus we may expect to measure spatial distributions with a resolution 0.1 - 1m over a distance 100m, to an accuracy $OM1%. This paper summarizes the principles of DOFS, gives examples of systems which have been studied, and gives some indication as to what is in store for the future.

The discovery of high-temperature superconductors (HTS) has opened new opportunities for applications of superconductors in optoelectronics. The HTS perovskites represent a new class of solid-state materials, exhibiting many very interesting and potentially useful electronic, optical, and electro-optical properties. They also operate in the 30-80 K temperature range, where refrigeration is cheap and the parameters of semiconducting devices are optimal. A review of the substrate materials and deposition techniques suitable for fabrication of high- quality epitaxial HTS films for electronic and optoelectronic applications is given. Laser processing techniques of HTS films are presented, with a special emphasis put on the laser writing method, which enables definition of superconducting and nonsuperconducting regions in the same, epitaxial HTS film. Two possible approaches for the development of a complete optoelectronic system with the elements based on the HTS films and operational at liquid- nitrogen temperatures are presented. The first approach consists of manufacturing the devices made of conventional electro-optic materials and containing HTS transmission lines and electrodes. Design and properties of ultrafast HTS interconnects are discussed, and a new concept of the Mach-Zehnder-type YBa2Cu3O7-y-on-LiNbO3 optical modulator is introduced. The second, more futuristic approach, is to exploit contrasting properties of the oxygen-poor and oxygen-rich HTS phases to fabricate novel, monolithic devices. Recent experiments are discussed, which reveal intriguing optical properties of HTS films, and are most relevant for the development of all-HTS optoelectronic devices. Several practical devices, such as high-frequency modulators, ultrafast-pulse generators, and sensitive photodetectors will be presented.