Three techniques for chemical detection are outlined which are based on the use of optical interferometric methods and permit highly sensitive detections of physical parameters. The coated-fiber interferometer concept is described in terms of an optical fiber coated with palladium that can detect hydrogen. A semitransparent metal-film sensor is then described which can be used for interferometric chemical transduction to detect chemical species. The polymer-swelling sensor is based on physical absorption such as in the use of multimode fibers with polymer films deposited on the end. Specific attention is given to the conditions for device sensitivity for the interferometric techniques presented, and the devices are shown to have selectivities that are lower than those of spectroscopic methods. The sensitivity of chemical transduction can be beneficial in a number of the measurement environments discussed.
Hollow waveguides offer applications in remote thermometry and spectroscopy because they transmit infrared radiation and possess chemical and mechanical durability, coupled with high melting points. As in solid dielectric optical fiber, the radiation is propagated by total internal reflection when the refractive index of the cladding is less than that of the air core (n
An overview is given of intrinsic fiber-optic chemical sensing encompassing refractometric sensors, evanescent spectroscopic sensors, coated-fiber sensors, and core-based sensors. Specific attention is given to techniques that are being tested such as commercial fluoroimmunoassay probes, evanescent-wave sensors for monitoring composite curing, and liquid-level monitors based on refractometric sensors. Of particular interest in the realm of research are intrinsic fiber devices that employ dyes and similar intermediaries to enhance the response of the sensors. Sensors that employ such intermediaries are expected to provide greater sensitivity to target analytes. The sensor techniques presently under development are also concluded to be useful for air-quality monitoring, and specific projects are discussed that are aimed at sensing gaseous species.
We have recently demonstrated the use of renewable reagent fiber optic sensors in a harsh sample matrix and with multiple reagent chemistries. Sodium hydroxide concentrations ranging from 1. 5-23. 0 (w/w) (0. 38-7. 2 M) were measured with a single probe chemistry. A sensor for free and total chlorine has been developed in which the reagents were sequentially switched to make the sensor responsive to either free chlorine (N 1 4-phenylene-diamine (DPD) + phosphate buffer) or both free and combined chlorine (DPD + phosphate buffer + KI). The detection limit of free chlorine was 0. 05 mgfL Cl2 at a reagent flow rate of4 j. tLtmin and covering a dynamic range of 0. 05-25 mg/L Cl2. Improvements in sensor fabrication techniques are currently being investigated in order to increase overall sensor functionality.
Optical fibers with layers of glass-ceramics are considered and tested with respect to their use in different environments as single- and multimode lightguides. Glass-ceramic optical fibers are tested that have different material compositions, cross-section topologies, and coefficients of thermal expansion (CTEs). Stress-induced optical phase-temperature effects can be studied with glass ceramics that have CTEs of around zero, and the glass ceramic sensors are compared to nontreated fibers to study the dependencies of the fibers'' parameters on induced stress and temperature. The application of glass-ceramics with various values of linear CTE to the fibers is studied to scale the characteristics of a glass-ceramic fiber-optic thermometer for several temperature ranges. The sensor can be stabilized when the pure stress-temperature effect is isolated. These glass-ceramic optical fibers are shown to provide unique characteristics for the use of fiber-optic measuring devices in certain measurement environments.
An Automated Fiber Optic Moisture Sensor System (AFOMSS) being developed for use in the food processing industry at Stevens uses an IBM AT compatible computer the PC 63 10 to control optical components and acquire process and display temperatureand humidity data. This information maybe used to controlfoodprocessing operations. Automated moisture sensor system operation has been validated using a Mitsubishi HS-4 electronic moisture sensor and fiber optic moisture sensors provided by the Rutgers Fiber Optic Materials Research Program (FOMRP). Real time measurements using a CoCl2-coated porous fiber optic sensor were found to be within 3 of the calibration data.
Prior work has reported on the usefulness of fiber optic sensors in detection of aromatic organic ground water contaminants such as the benzene toluene ethylbenzene and xylenes (BTEX) fraction of petroleum fuels. Our device is essentially a laser fluorimeter using fiber optic sensors for in-situ measurements. Both field and laboratory work have exhibited limits in the dynamic response range of fluorescence signal versus concentration when excitation occurs in the ultraviolet (266 nm). Potential causes of the observed shallow fluorescence versus concentration response include self-absorption at high concentration and stray light or electronic noise at low concentrations. The observed wide dynamic range resulting from visible excitation (532 nm) is used as a basis for comparison with UV performance. Selfabsorption phenomena are evident from the data at high contaminant concentration but practical applications more often are concerned with low concentrations. Lower limits of detection observed in UV excitation experiments are evaluated as to the possible sources of stray light including fiber luminescence coupling between the excitation and collection fibers in the sensor elastic scattering and reflection signals in the excitation module and spectral impurities in the laser excitation light from the laser flashlamp. Coupling and fiber luminescence in the sensor have been evaluated and resolved the excitation module has been redesigned to reduce potential scattering and the laser source continues to be investigated. 1 . LASER-INDUCED FLUORESCENCE TECHNIQUE Our research group has been
The First Omega Group Inc. has developed a low cost optical fiber sensing technique for detecting the presence of oils gasoline organic solvents and other oily contaminants in soils. The sensing means consists of a continuous optical fiber having a portion of its surface specially processed to render it sensitive to the presence of soil contandnants. The processed area of the fiber is positioned within the environment that is at risk of contaniination. Contact by a contaminant with the processed area of the optical fiber changes the attenuation of infrared light through the processed area in a characteristic way and in real time. The change in light attenuation is detected using a conven tional photo detector to provide indication of contamination within the soil.
Fiber optic sensors typically suffer from environmental effects that result in drift temperature sensitivity and bending induced inaccuracies. This paper describes a rugged fiber optic pressure sensor free of these inaccuracies and suitable for environmental and process control applications. A high degree of stability and accuracy is achieved through the use of wavelength referencing and in-situ calibration techniques. The critical issues for performance described in the paper are related to the opto-electronic interface the fiber link and the sensing element. Commercialization issues are also addressed.
The efficiency of core-light injection from sources in the cladding of an optical fiber is modeled analytically by means of the exact field solution of a step-profile fiber. The analysis is based on the techniques by Marcuse (1988) in which the sources are treated as infinitesimal electric currents with random phase and orientation that excite radiation fields and bound modes. Expressions are developed based on an infinite cladding approximation which yield the power efficiency for a fiber coated with fluorescent sources in the core/cladding interface. Marcuse''s results are confirmed for the case of a weakly guiding cylindrical fiber with fluorescent sources uniformly distributed in the cladding, and the power efficiency is shown to be practically constant for variable wavelengths and core radii. The most efficient fibers have the thin film located at the core/cladding boundary, and fibers with larger differences in the indices of refraction are shown to be the most efficient.
We studied a fiberoptic electrical sensor to detect electrical discharge light in a gas insulated system using a plastic optical fiber doped with an organic fluorescent compound which can absorb and emit light. We measured the spectrum of SFs gas by spectroscope using needle electrodes in a sealed glass tube. The spectrum is bluish and dis continuous and in the range of about 330 nm to 600 nm. The wavelength corresponding to the maximum emitted optical strength is 429 nm. The spectrum does not change when the electrode gap and the gas pressure are varied. Fiber doped with fluorescence which is the most useful for sensing the discharge light in SFs gas has been developed. The conversion efficiency was determined using monochromatic light produced by a xenon lamp with color filters. The conversion efficiency of the improved fiber doped with BBOT is on the order of 0. 01 for incident light of 406 nm.
The luminescence emission (652 nm) and lifetime (390 ns) of a novel Ru(II) tris-chelate complex tris(2-(2-pyrazinyl)thiazole)ruthenium(II) are quenched by H30 and other acids (phosphoric acetic phthalic and dihydrogenphosphate) in aqueous solution. The quenching process is shown to occur via a proton transfer to the excited (triplet state) complex since the ground state complex undergoes no protonation in the 0-12 pH interval (pKai 1. 9). Quenching rate constants in the range 1 x 108 to 5x iO M1s1 have been measured. The pH transducing system has been tested in solution using carbon dioxide and has been applied to the construction of a bifurcated fiber optic chemical sensor for this gas. Advantages of employing Ru(pzth)32 as a luminescent dye includeamong others: (1) a hydrogen carbonate buffer is not required in the reservoir chamber and (2) excitation in the visible region using inexpensive plastic optical fibers and collection of the emission through cut-off filters is feasible.
We present fluorosensors for potassium calcium and ammonium based on the use of ion carriers and a highly fluorescent lipophilic proton carrier. Fluorescent potassium-sensitive membranes have been prepared by dissolving chemically modified Nile Blue and valinomycin in a pvc/plasticizer mixture. Valinomycin being a highly selective potassium carrier binds potassium ion and carries it into the membrane. Simultaneously in order to maintain electro-neutrality of the membrane a proton dissociates from the proton carrier (Nile Blue) dissolved in the pvc membrane and diffuses into the aqueous phase. The dissociation of the protonated amino group of Nile Blue causes its color to change from blue to red. Depending on the choice of the excitation wavelength both the decrease in the fluorescence of the blue species and the increase in the fluorescence of the red species can be monitored. The sensor fully reversibly responds to potassium over the 100 uM to 100 mM concentration range. By replacing valinomycin by carriers for ammonium and calcium ion the respective sensors are obtained. It also is found that the addition of hydroxylic plasticizers to the membrane material considerably accelerates the response time in both directions. While this kind of sensor suffers from cross sensitivity toward pH it has the advantage of full solid-state compatibility (LEDs or diode lasers may be used as light sources). Also because only one kind of fluorophore can be used in almost all kinds
An analysis of the state of the art in pH sensing by optical fibers is presented. Advantages and drawbacks of this type of measurement are described. Different techniques in the optrode construction are taken into consideration and particular attention is also devoted to the overall optoelectronic system which must satisfy definite market requirements.
The use of distributed and multiplexed fiber-optic sensors in the process monitoring and control environment is described. Recent application development work based on OTDR signal processing techniques is reviewed. Applications investigated include distributed temperature sensing strain sensing humidity sensing chemical sensing and distributed alarm sensing. Multiplexable fiber-optic sensing applications including edge sensing distance sensing vibration and particle sizing based on photon correlation spectroscopy are also described. The principles underlying these measurement techniques are presented and process application examples are provided.
In this paper we report on the development of a fiberoptic sensor using a new detection method based on the Surface-Enhanced Raman Scattering (SERS) technique. The SERS effect is based on recent experimental observations which have indicated enhancement of the Raman scattering efficiency by factors up to 108 when a compound is adsorbed on rough metallic surfaces having submicron protrusions. In this report we describe the development of the SERS probes for in situ remote sensing.
An accurate spectrophotometric study on acid-base indicators immobilized by a silylation process is described. Immobilization modifies the acid-base properties of the indicators: a comparison with their behaviour in solution was made. Particular care was paid to the presence of hysteresis to the sensitivity and also to the peak wavelength. Early measurements performed with optical fibers were also described.
Attempts have been made to determine two analytes simultaneously using one optical indicator. Two approaches were pursued: The first is based on multi-wavelength amplitude analysis of the fluorescence excitation or emission spectrum and the second on amplitude/lifetime analysis of the emission spectrum of a single indicator. Both methods are suitable for determination of two species if one affects the electronic ground state and the other the excited state.
Evanescent wave sensors based on single mode waveguides are attractive but have rather low sensitivities for gaseous species and suffer degradation from surface contaminants. We propose the use of a thin high-index loading film on a silica waveguide to enhance the field strength at the guide surface and to correct measurements for surface contamination by launching the two polarisation modes. Resonant structures also enhance sensitivities when matched to the absorption characteristics of a gas.
Polymeric optical waveguides were employed as sensors, based on the chemical interaction of the polymer with its environment. As the polymer preferentially absorbs chemicals from a sample matrix, the waveguiding properties of the polymeric film change. These changes in the refractive index and the thickness of the film are expressed as shifts in the waveguide propagation modes, which can be monitored to provide a very reproducible sensor signal. Because the waveguides are typically less than one micron thick, these sensors also have short response rates. An evaluation of the responses of several polymeric thin film waveguides and their cross sensitivities is presented.
A broadly focused laser beam was used to investigate simultaneous excitation of multiple modes in prism and grating coupled polymer thin film optical waveguides. Concurrent coupling of two lines from different lasers through a fiber bundle was also examined. Results indicate that simultaneous multiple pathlength and multiple source sensing at the surface of thin film waveguides is feasible.
A fiber optic sensor measured the rate of ion exchange for metal cations between a solution 4ivironrnent and silica core surface. The ion exchange of Pb was observed to be both reversible and reproducible. Further by competitive displacement of cations the exchange selectivities for a series of metals were confirmed. I.
A novel immunosensor concept monitors antigen-antibody binding on the surface of a planar single-mode waveguide. The concept can be used as the basis for a label-free homogeneous immunoassay because only changes in the thickness and refractive index of the antigen-antibody layer are monitored by observing small changes in the effective index of the waveguide. BSA +anti- BSA binding was examined theoretically using a four-layer model and effective index measurements were obtained which agreed with the calculated values. Analysis indicated that the small effective index changes can possibly be measured with high sensitivity and at low cost using an integrated optic interferometer format.
The key to a successful fiber optic sensor design is to maximize the interaction between the optical radiation carried in the waveguide and the chemical species. Of the various designs that have been discussed evanescent and end fire have been the most widely used in chemical sensing. These approaches are best with fluorescent chemistry systems. Absorbance based optical fiber sensing systems offer the advantages of being adaptable to a wider variety of sensing chemistries. Historically single fiber systems for absorbance sensing have not been feasible without having an external mirror attached to the fiber end. The external attachment of the sensing chamber and mirror increase the size fragility and cost of the sensor. We have developed a novel single fiber sensor that shapes the end of the fiber into an optical element and places the chemistry within the fiber itself.
Combining fluoroimmunoassay principles and fiber-optic fluorimetry has extended the available transduction schemes for development of fiber-optic sensors. Three representative designs are discussed focusing on a sensor configuration utilizing a controlled-release polymer to sustain a release of indicating reagents over long periods. This novel approach has been adapted for pesticide monitoring. A model system has been designed that releases the reagents of a homogeneous fluoroimmunoassay from an ethylene vinyl acetate polymer for the detection of atrazine. The sensor utilizes a competition reaction between fluorescent-labeled and unlabeled atrazine for the available binding sites on labeled anti-atrazine antibodies.
We have developed a differential-absorption fiber-optic sensor for use in groundwater and vadose zone monitoring of certain volatile organochiorides. The principle of detection is a quantitative irreversible chemical reaction that forms visible light-absorbing products. The sensor has been evaluated against gas chromatographic (GC) standard measurements and has demonstrated accuracy and sensitivity sufficient for the environmental monitoring of trace levels of trichioroethylene (TCE) and chloroform. This sensor is currently under evaluation in monitoring well and vadose zone applications. In this paper we describe the principles of the existing single measurement sensor technology and show preliminary field test results.
Monoclonal antibodies were covalently bonded to the surfaces of planar waveguides to confer immunoreacth''ity. Silver-ion diffused waveguides were used to measure theophylline concentrations in a fluorescence immunoassay and silicon nitride waveguides were used to detect theophylline in an absorbance-based immunoassay. Liposomes were employed in both assays as the optically detectable label in a competitive reaction to monitor antigen-antibody complexation. Regeneration of the active antibody site will be discussed.
We present a scheme for sensing optical isomers (enantiomers) of biogenic amines such as the Bblocker propranolol. Recognition of one of the enantiomers of propranolol is accomplished by specific interaction of the amine (which is present in the protonated ammonium form at physiological pH) with an optically active substrate (dibutyl tartrate) in a pvc membrane. As the ammonium ion is carried into the pvc membrane a proton is simultaneously released from the proton carrier (a lipophilic phenolic xanthene dye which undergoes protolytic dissociation in the pvc membrane) which thereby suffers a color change. The sensor responds to propranolol but also to other biogenic amines such as 1-phenylethylamine and norephedrine in the 20 pM to 10 mM range but has a pH-dependent response. The selectivity factors depend on the type of receptor and range from 0. 0 to 0. 30.