Brian G. Healey

Simultaneous monitoring of pH, CO2 and O2 using an optical imaging fiber

The interdependence of pH, CO2 and O2 during chemical and biochemical processes has driven the need to monitor them simultaneously, continuously and in situ, in order to exert better control over such reactions. We present the fabrication and performance of a multi-analyte imaging fiber sensor that allows pH, CO2 and O2 to be monitored simultaneously with rapid response. Sensing elements are fabricated by covalently immobilizing fluorescent indicators within polymer matrices via photopolymerization, resulting in the formation of distinct regions of analyte-sensitive polymer at the fibers distal end. The multianalyte sensors working range is 0%–100% for O2 and 0%–10% for CO2 in the pH range 5.5–7.5. The sensor was used to monitor the pH, CO2 and O2 changes during a beer fermentation.

Photodeposition of micrometer-scale polymer patterns on optical imaging fibers

Microstructures were fabricated on optical imaging fibers with a photopolymerization technique. Monodisperse polymeric microarrays were produced containing spots of 2.5 micrometers in diameter spaced 4.5 micrometers apart. Polymer microarrays were also deposited on other substrates by using imaging fibers for light delivery. The technique allows micrometer-scale photopatterning with masks larger than the desired dimensions.

Development of a penicillin biosensor using a single optical imaging fiber

A penicillin biosensor has been fabricated by photodepositing penicillin-sensitive polymer matrices and pH-sensitive polymer matrices on different regions of an optical imaging fiber. Penicillin is detected by coupling the enzymatic activity of penicillinase with the pH sensitivity of fluorescein. Penicillin concentration is correlated to the pH change in the microenvironment of the penicillin-sensitive matrix relative to the pH of the sample solution. This dual sensor removes the need to maintain a constant solution pH when measuring penicillin and should enhance greatly the application of biosensors.

Multianalyte biosensors on optical imaging bundles

We present an optical biosensor design that expands the utility of enzyme biosensors. These biosensors are fabricated by site-selective photodeposition of analyte-sensitive polymer matrices on optical imaging fibres. These dual-analyte arrays allow for the simultaneous, independent measurement of the analyte of interest and the transducing analyte. The first integrated optical-biosensors using this design have been prepared that allow both the dependent and independent analytes to be measured simultaneously, for example penicillin and pH (Healey & Walt, 1995) or glucose and O2 (Li & Walt, 1995). Independent measurement of the transducing analyte allows penicillin or glucose to be quantitated in the presence of a concurrent pH or O2 change, respectively. Penicillin can be measured in the range 0.25-10.0 mM in the pH range 6.2-7.5. Glucose can be measured in the range 0.6-20.0 mM in the O2 range 20-100%. The utility of the sensor design was demonstrated by using the penicillin-dual-analyte biosensor to quantitate penicillin produced during a Penicillium chrysogenum fermentation.

Fiber optic array sensors as an architecture for an artificial nose

Imaging optical fibers can be used in conjunction with 2D detectors such as CCD cameras to fabricate array sensors. These sensors contain spatially separated photopolymers containing analyte-sensitive fluorescent indicators on an imaging fiber tip. Spatial resolution of the indicators is maintained through the imaging fiber array and projected onto a CCD detector. Sensors have been fabricated using the conventional one analyte-one sensor paradigm. This approach has resulted in multianalyte sensors for blood gases, process control parameters, and environmental contaminants. An entirely different approach is also being taken. Sensing sites containing cross-reactive indicator regions are deposited on the end of the imaging fiber. The resulting array is then challenged with a variety of analytes. Pattern recognition algorithms are employed to train a neural network. The resulting sensor array can identify subsequent challenges with the analyte even after extended use.

Oxygen Sensing Properties of a New Ruthenium (II) Compound

Abstract The design of efficient oxygen measuring devices has important environmental, clinical and process control applications. Several methods are available for oxygen quantitation, but those based on the dynamic quenching of luminescence of inorganic compounds have several advantages. In this work the oxygen-quenching luminescence characteristics of a newly synthesized ruthenium (II) compound immobilized on an optical fiber was investigated using Stern-Volmer kinetic analysis. Results obtained show that the luminescence intensity of the newly synthesized compound exhibits a second order dependence on oxygen concentration from 0–100 %. The oxygen sensing characteristics of this new compound are comparable to other conventional oxygen sensing compounds.

Simultaneous monitoring of O2, CO2, and pH using a 200-micrometer optical imaging fiber

A multi-analyte sensor has been prepared that allows O2, CO2 and pH to be monitored simultaneously with rapid response to all three analytes. The sensor is fabricated to photodepositing analyte-sensitive polymer matrices on the distal surface of an imaging fiber. The array shows sensitivity to pH in the range 5.0 - 8.0, CO2 from 0 - 15% and O2 from 0 - 100%.

Development of sensor arrays for continuous groundwater monitoring

Industrial development has led to the release of numerous hazardous materials into the environment, posing a potential threat to surrounding waters. Environmental analysis of sites contaminated by several chemicals calls for continuous monitoring of multiple analytes. Monitoring can be achieved by using imaging bundles for the fabrication of sensors. Imaging bundles are formed by melting and drawing together several thousand individual optical fibers. The fibers are drawn coherently so that the position of an individual fiber of the bundle at one end (distal) corresponds to the identical position at the other end (proximal). By coupling imaging fibers to a charge coupled device (CCD), one has the ability to spatially discriminate the distal end of the fiber.

Optical microsensor arrays

Fiber optic imaging bundles are comprised of thousands of individual fibers melted and drawn together in a coherent manner. Sensor arrays are fabricated by combining the optical pathways of imaging fibers with the spatial discrimination of CCD video cameras.