Steven M. Barnard

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.

Chemical sensors based on controlled-release polymer systems

A novel chemical sensor has been developed in which the polymer ethylene-vinyl acetate is used as a controlled-release system to deliver reagents to the sensing region of an optical fiber for a homogeneous competitive immunoassay based on fluorescence energy transfer. A competition reaction is used to enable continuous measurements of the solution antigen concentration. More generally, the technique allows irreversible indicating chemistries to be used in the construction of chemical sensors that can measure continuously for long periods. Although the sensor configuration has not been optimized in all respects, data are presented for a model system in which a fluorescein-labeled antibody and Texas Red-labeled immunoglobulin G (IgG) are used.

Fiber optic sensors based on time-release polymers

Fiber-optic sensors based on a controlled-release polymer provide sustained release of indicating reagents over long periods. This technique allows irreversible chemistries to be used in the design of sensors for continuous measurements. The first reported sensor used 8-hydroxypyrene- 1 ,3,6-trisulfonic acid and sulforhodamine 640 to measure pH continuously for three months in the range of 5.5 to 8.0 with a precision units. The sensor reported in this paper is based on a fluorescence energy transfer immunoassay. The sensor was cycled through different concentrations of antigen continuously for 30 hours. Although the sensor was not optimized, the data indicates the viability of the technique.

Antibody-based fiber optic sensors for environmental and process-control applications

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.