We demonstrate the use of a two-channel flowcell for fluorescent immunoassays. The flowcell contains a planar silica waveguide for evanescent excitation of the fluorophores, and the planar waveguide surface provides the solid support for immobilization of the antibodies. The detection system is composed of a grating spectrometer and a CCD camera for spectral characterization of the emitted signals. Two methods of sensing have been studied: a displacement-type technique and a sandwich-type assay. The sensitivity achieved for measuring concentrations of HCG by the sandwich method is sub-picomolar. Also, we have experimentally compared the signal strengths for two alternative ways of excitation and collection, and determine that waveguide excitation/side collection has some practical advantages over side excitation/waveguide collection.

We have shown that a direct-coupling approach can give a high throughput of light from a broadband IR source into a chalcogenide optical fiber. The high light levels in the fiber facilitate sensing based on evanescent-wave absorption. We place one end of a diamond rod in direct contact with an optical fiber of the same diameter, while the other directly contacts a hot IR source. This results in efficient coupling of a wide cone of optical modes into the fiber, including those propagating at nearly the cutoff angle (the critical angle for internal reflection from the fiber-liquid interface). These very high-order modes have a large penetration depth, a high interfacial evanescent wave intensity, and a large number of reflections per unit length. As a result, multimode spectra obtained by using them demonstrate high sensitivity, i.e. very large measured absorbances per unit length of fiber contact with sample. Using the diamond coupler with a 500-micrometers -dia. fiber, we observe an absorbance coefficient (alpha) _e of 0.04 M^-1 cm^-1 for the 1030 cm^-1 band of glucose in water. This sensitivity can be increased even farther (with little or no increase in the noise present in the absorbance spectrum) by tapering the portion of the fiber in contact with the sample. With a tapered fiber diameter of 200 micrometers , we observe an (alpha) _e of nearly 0.2 M^-1 cm^-1 for the glucose absorption band cited above. With either tapered or untapered fiber, it is possible to measure glucose concentrations in the range 0 - 250 mM with a sensitivity of < 25 mM in 2.5 min. With a 7-mm-long, 200-micrometers - dia. taper on the fiber, curled into an approximately 2-mm-dia. loop, 25 mM glucose can be detected in sample volumes as small as 20 (mu) L.

A micro-sized biosensor is formed using integrated-optic channel waveguides in a Mach- Zehnder interferometer configuration. The device measures refractive index changes on the waveguide surface, so it is called a biorefractometer. With an appropriate overlay or selective coating, the sensor can monitor proteins in blood or pollutants and bio-warfare agents in water. The waveguides are fabricated in a glass substrate using potassium ion exchange. A patterned glass buffer layer defines the interferometer's sensing and reference arms. A silicone-rubber cell arrangement brings sample analytes into contact with proteins immobilized on the integrated-optical waveguide surface. Data obtained for antigen-antibody binding of the proteins human Immunoglobulin-G and staph enterotoxin-B indicate that a 50 - 100 ng/ml concentration levels can be measured in less than ten minutes.

In recent years, the use of fiber optics has become an important tool in biomedicine and biotechnology. We are involved in developing and employing a new system which, through the use of fiber optics, may be capable of measuring the content of cholesterol and lipoproteins in blood samples in real time. In the optical fiber-based biosensor, a laser beam having a wavelength of 512 nm (green light) is launched into an optical fiber, which transmits the light to its distal end. An evanescent wave (travelling just outside the fiber core) is used to excite rhodamine-labelled HDL or LDL which become bound to the fiber or to fiber-bound molecules. The fluorescence (red light) is coupled back into the fiber and detected with a photodiode. Preliminary work has involved testing of high density lipoprotein (HDL) binding to a cholesterol-coated fiber and to a bare fiber and low density lipoprotein (LDL) binding to a cholesterol-coated fiber. A significant difference was observed in the binding rate of HDL (5 (mu) g/mL and lower) to a bare fiber as opposed to a cholesterol-coated fiber. The binding rate of HDL (5 (mu) g/mL) to a bare fiber was 7.5 (mu) V/sec and to a cholesterol-coated fiber was 3.5 (mu) V/sec. We have calculated the binding affinity of LDL to a cholesterol- coated fiber as 1.4 (mu) M^-1. These preliminary results suggest that the optical fiber-based biosensor can provide a unique and promising approach to the analysis of lipoprotein interaction with solid surfaces and with cholesterol. More importantly, the results suggest that this technique may be used to assess the binding of blood proteins to artificial organs/tissues, and to measure the amount of cholesterol, HDL and LDL in less than a minute.

Fiber optic technology and optical fluorescence have made the continuous monitoring of arterial blood gases a reality. Practical products that continuously monitor blood gases by use of an invasive sensor are now available. Anesthesiologists and intensive care physicians are beginning to explore the practical implications of this technology. With the advent of intra- arterial blood gas monitors it is possible to assess arterial blood gas values without the labor intensive steps of drawing blood and transporting a blood sample to the lab followed by the actual analysis. These intra-arterial blood gas monitors use new optical sensor technologies that can be reduced in size to the point that the sensor can be inserted into the arterial blood flow through a 20-gauge arterial cannula. In the best of these technologies the sensors accuracy and precision are similar to those in vitro analyzers. This presentation focuses on background technology and in vivo performance of a device developed, manufactured, and marketed by Puritan-Bennett Corporation.

New fluorescence based optical fiber sensors have been developed for the monitoring of pH, Carbon Dioxide, and Oxygen in radial arteries. These sensors utilize wavelength multiplexing for detection of three parameters with one optical fiber. Unlike sensing systems in which separate fibers are used for each parameter, wavelength multiplexed systems have the potential for parameter to parameter optical interference. We refer to this interference as 'crosstalk'. Wavelength multiplexed systems and their potential for crosstalk are described. Investigating methods for obtaining independent isolation of multiple parameters under laboratory conditions are discussed. Computational methods of quantifying crosstalk are shown. Specific test protocols are provided, along with representative test results. Minimal crosstalk was found in the systems tested.

Colorimetric fiber optic sensors have been developed for measuring the pH and pCO₂ of blood. These sensors are fabricated using a single 125 micrometers diameter optical fiber. Located at the distal end of the fiber is a capsule that contains a pH sensitive dye. The pCO₂ sensor is fabricated from a pH sensor with the addition of a salt, bicarbonate, and the encapsulation with an ion impermeable gas permeable membrane. The distal end of the capsule is terminated with a reflective surface. The reflective surface can either be a polished metallic surface or, in this case, a TiO₂ impregnated epoxy. The disposable sensor mates with an optical connector that contains two optical fibers of the same size as the disposable sensor. The two fibers within the optical cable provide a light path for both the antegrade and retrograde optical signals. These fibers are terminated at either the LED source or the detector. A prototype sensor assembly that incorporates the measurement of three physiological parameters (pH, pCO₂, and sO₂) has been demonstrated to fit within a standard 20 gauge arterial catheter, typically used for radial artery blood pressure monitoring, without significant damping of the blood pressure waveform. The pH sensor has a range of 6.9 - 7.8 with a precision of 0.01 pH units and the pCO₂ sensor has a range of 15 - 95 mm Hg with a precision of 3 mm Hg. The long term drift pH drift is less than 0.01 pH unit per 8 hours and the pCO₂ drift is less than 1 mm Hg per 8 hours. Sensor performance in the canine has demonstrated that the pH sensor is accurate to within +/- 0.03 pH units and the pCO₂ sensor is accurate to within +/- 3 mm Hg when compared to a typical blood gas analyzer.

We have developed a silica-filled, noncrosslinked, organosilicon matrix for trapping a luminescent dye. The matrix is used for fiber optic oxygen sensing based on the luminescence quenching phenomenon. The rheological properties of the matrix material are such that it simplifies fabrication of the extremely small sensors required for intra-arterial applications. The dye seems to be distributed between sites in the continuous organosilicon phase and the dispersed silica phase. The relative populations in the two phases can be adjusted by certain additives which generate compounds that elute silica, such as acetic acid. The quenching constant of the system depends not only on the presence or absence of such eluants, but on the chemical nature of the additive as well. We were able to tailor the composition of matrix so as to optimize the sensitivity over the physiological range of oxygen concentration. Our observations on the composition dependence of the oxygen sensitivity of the matrix are presented.

The general background and theoretical aspects involved in making a broad-range fiber-optic pH sensor will be discussed. A dye-indicator-based pH measurement depends on the equilibrium position between two or more colored forms of a dye--the ratio of the colored forms is a function of pH.

This paper describes preliminary results on the development of a fiber optic pH sensor for gastric measurements. As the pH values in the gastric system vary from approximately 1 to 7, a combination of appropriate dyes to cover this broad range should be used. pH colorimetric indicators bound in polyacrylamide microspheres and light scattering particles are packed in a cellulosic dialysis tubing at the end of a pair of plastic optical fibers. The experimental setup uses a CCD spectrometer as a detector and a 386 compatible personal computer. All parameters can be set by software. Results with both one-dye and two-dye pH sensors are presented.

A novel fiber optic transducer has been developed for continuous monitoring of physiological pH. In the current embodiment, the miniature transducer was evaluated for intracutaneous pH monitoring within the conjunctiva! mucosal membrane in anesthetized juvenile pigs. A vasodilator was administered percutaneous prior to insertion of the transducer to minimize localized ischemic reactions. During the 5-6 hour trials the data from the fiber optic transducer was compared to an in dwelling electrochemical pH micro-electrode in close proximity. The test subject's vascular pH was manipulated via a pressure-cycled respirator. Through a combination of adjustments made to the BPM(breaths per minute), PIP(peek inspiratory pressure), and Fi02(% oxygen in respiratory mix), arterial pH levels were made to change by as much as 0.5 pH units over a range of 7.2 to 7.7 pH without significant detriment to the test subject. A skeletal muscle relaxant was administered frequently in addition to the anesthesia to limit ventilator compromise. Arterial blood gases were monitored through conventional blood gas analysis equipment. Additionally, arterial and venous pressure and wave form, EKG and expired C02 were continuously monitored to follow the test subjects physiologic state. In one representative trial run, the mean(±SD) difference between the fiber optic transducer and the electrochemical pH micro-electrode measurements was no greater than 0.080±0.050 pH units. Further, there was a strong interrelation between the tissue pH and the arterial pH measurements. In vitro stability tests showed that in buffered saline at pH=7.4 and 37°C, the transducer presented no greater than 0.048 pH unit drift in approximately six(6) hours. Stability tests in porcine blood under the same conditions indicated a drift of no greater than 0.015 pH units in approximately six(6) hours. One unique feature of this approach throughout the study was that the test units were freeze-dried and gamma sterilized for storage and subsequently reconstituted and calibrated immediately prior to use. This obviates the problems normally associated with wet storage of devices such as these.

The distal tip of a 200 micrometers imaging fiber comprised of thousands of 2 micrometers fibers is coated with a thin layer of pH sensitive material. Polymerization is initiated thermally, and results in a uniform coating of polyHEMA/fluorescein on the order of 10 micrometers thick. Performance data for this fiber demonstrates it is capable of simultaneous pH measurements and near field imaging.

A high sensitivity, batch fabricated, micromachined pressure sensor with interferometric readout is described. The transducer consists of a fiber V-groove, a 45 degree(s) stationary mirror and a silicon membrane, which are micromachined in two separate silicon wafers by anisotropic etching in KOH solution. The 45 degree(s) mirror provides a means of directing the light to and from the membrane with a horizontally mounted fiber, which is compatible with etched V-groove fiber alignment and positioning. A Fabry-Perot optical cavity is formed between the end of the fiber and the silicon membrane. The generated optical interference fringes are used to detect and measure the change in membrane deflection. The pressure range of operation and sensitivity are dictated by the thickness, size and material of the membrane and the wavelength of the light source. The sensor described here is designed for implantation in living bone tissue for the detection of necrosis. The ultimate, minimum size for this sensor is dictated by the diameter of one, single mode fiber, e.g. 125 microns.

Optical sensing systems for medical diagnostics have improved significantly in recent years. Many systems are now commercially available and provide greater reliability and sensitivity and/or improved responsiveness than previous systems. A key to the technology improvement has been an increased variety of optical fiber designs available for each optical system. The two primary types of fibers used in biomedical sensors are all-plastic and silica-core glass fibers. Each fiber family is identified and differentiated. The parameters discussed include sizes commercially available, numerical aperture ranges, spectral attenuation and ranges, mechanical strength and flexibility, and temperature compatibility. Data for six fiber types is presented. The applications of venous catheter oximeters and arterial blood gas analyzers are also discussed. Common design considerations and optical fiber limitations are reviewed. The tremendous diversity in optical fiber systems requires a large selection in optical fiber technologies. The design engineer must carefully evaluate the optical, environmental, and mechanical requirements of a biosensor system in order to choose the most appropriate optical fiber.

The use of fiber optics in communications and data transmission applications has become wide spread in the last decade. At the same time fiber optic sensors have not gained wide commercial acceptance even though many are known and indeed numerous U.S. and foreign patents have been granted. Camino Laboratories a small medical device concern has successfully marketed a fiber optic pressure monitoring system and become a leader in the area of intracranial pressure (ICP) monitoring. Some curiosity about the company and its products has been expressed. This presentation will briefly give a background of the company, an explanation of the product, an account of the transfer from concept to volume manufacture and a word on limiting drawbacks of an intensity modulating fiber optic sensor.

A novel velocimeter for the measurement of blood velocity in veins and arteries is described. It consists of a semiconductor laser, coupled to a glass fiber, to be inserted in the flow, and applying self-mixing as the detection technique. Theoretical aspects and in-vivo and in-vitro measurements are described and discussed.

A fiber optic radiometer based on a cooled photonic detector was designed and constructed. The radiometer was capable of measuring in real time the temperature of a tissue irradiated with CO₂ laser. A silver halide I.R. fiber was used to deliver the CO₂ laser radiation needed to irradiate the target, and also to deliver the thermal radiation emitted from the target back to the detector. Two methods of measurements were examined, both of which solve the problem of the reflected CO₂ radiation which blinds the detector. A theory for silver halide fiber optic radiometer based on lock in amplifier techniques is presented. Discussion of the radiometer design and construction is given. This work can be a good basis for the subject of measuring, in real time, radiometric signals caused by CO₂ laser irradiation. Such a radiometer is of great use, when dealing with Photo Thermal Radiation, P.T.R., with 10.6 micrometers , CO₂ laser wave length, which is very useful in medicine and industry.

The heating of tissue by microwave radiation has attained a place of importance in various medical fields such as the treatment of malignancies, urinary retention and hypothermia. Accurate temperature measurements in these treated tissues is important for treatment planning and for the control of the heating process. It is also important to be able to measure spacial temperature distribution in the tissues because they are heated in a non uniform way by the microwave radiation. Fiber optic radiometry makes possible accurate temperature measurement in the presence of microwave radiation and does not require contact with the tissue. Using a IR silver halide fiber optic radiometric temperature sensor we obtained accurate temperature measurements of tissues heated by microwave, enabling us to control the heating process in all regions of the tissue. We also performed temperature mapping of the heated tissues and demonstrated the non-uniform temperature distributions in them.

A fiber optic magnetic gradiometer has been successfully configured to detect the cardiac magnetic field. The gradiometer is comprised of a Mach Zehnder interferometer, with extremely thin transducers to allow placement of the sensor very near to the chest of a human subject. The sensor detects the cardiac magnetic field in real time, and demonstrates good fidelity in both the time and frequency domains, with only a low pass filter used for signal processing. To our knowledge, this is the first detection of a biomagnetic signal with an optical sensor.

A chemiluminescence fiber optic biosensor system coupled to FIA was developed to measure glucose in bodily fluids. Glucose oxidase was immobilized on a preactivated nylon membrane and attached to the tip of a fiber optic bundle. This enzyme acts on (beta) -D-glucose to produce hydrogen peroxide which was then reacted with luminol in the presence of ferricyanide to produce a light signal. The sensitivity of the biosensor was determined to be 32 +/- 0.65 nV (mu) M^-1 with a minimum detectable level of 5 (mu) M. The addition of a glucose oxidase column with a higher enzyme loading improved the sensitivity by at least 25-fold thus permitting the measurement of the lower glucose levels found in urine. The enzyme membrane could be reused for at least 50 analyses while the glucose oxidase column could be reused for over 500 analyses without losing the original activity. Endogenous ascorbate and urate usually present in urine samples which interfere with the chemiluminescence signal were effectively retained by an upstream ion exchange column. When applied for the determination of urinary and blood glucose levels, the results obtained compared well with those of the widely accepted hexokinase assay.

We present experimental results from fiberoptic spectroscopy apparatus measuring whole blood's optical attenuation over a continuous wavelength range of 0.6 - 1.0 micrometers . Relative optical density (OD) spectra at a number of hematocrit values and oxygenation levels is obtained. The role of hematocrit in affecting spectral shape is discussed based upon relatively simple relationships derived from experimental data. A specific partial differential equation emerges from the analysis. This equation relates scatter-dependent experimental OD to oxygen saturation, hematocrit and purely absorbing, nonscattering constituents--and is obeyed over an extended wavelength range. A three-wavelength algorithm using experimental absorbances at LED-compatible wavelengths accurately provides both hematocrit and oxygen saturation values, for hematocrit levels between 0.2 and 0.6 in the presence of oxygenated and reduced Hb species. Optical system comparison between spectroscopic data and modeled LED behavior indicates the algorithm can be mapped to the design and implementation of discrete components for clinical use.

A fiber optic chemical sensor is presented which utilizes surface plasmon resonance excitation. The sensor is advantageous since it eliminates the traditional bulk optic prism in favor of a relatively simple and inexpensive design. This configuration allows for remote sensing and multiplexing. The sensing element of the multi-mode fiber optic has been fabricated by removing a section of the fiber cladding and symmetrically depositing a thin layer of highly reflecting metal directly onto the fiber core. A white light source is used to introduce a range of optical wavelengths into the optical fiber. A fiber optic spectrograph is used at the output of the fiber optic sensor to measure the transmitted spectral intensity distribution (light intensity versus wavelength). There are two sensor configurations presented. The system should find general utility as a dip-probe for quantification of proteins in solution.