Planar integrated optical waveguide chemical sensors and novel transducer layer materials

Abstract

The application of planar integrated optical waveguide (IOW) technology to chemical sensor development results in very sensitive, fast-response devices. The additional dimension of selectivity that is possible in these devices, through the ability to select an analytical wavelength of light particular to only a specific interaction, is also a very attractive feature. The implementation of sol-gel materials processing in the sensor fabrication proves beneficial to the device performance in many ways. Sol-gels provide the high optical quality materials used in both the waveguiding layer and indicator film overlayers of the planar IOW chemical sensors. Since they are chemically prepared, their physical properties and chemical properties are easily tailored through chemical means or processing conditions. The fact that sol-gel bulks and films are prepared at room temperature allows the immobilization of heat labile species such as organic indicators or, in the case of biosensors, proteins or enzymes. The feasibility of the laminate planar IOW sensor geometry is demonstrated through the formation strongly light-absorbing complexes between the analytes and sol-gel immobilized indicators, detected by the attenuation of totally internally reflected light guided in the IOW (Part I). The construction of a gas-phase humidity sensor is shown in Chapter 3, along with a solution-phase sensor for aqueous isopropyl alcohol (IPA) in Chapter 4. An IOW-based humidity sensor utilizing a completely non-sol-gel based transducer layer is also reported (Chapter 5). The humidity sensors were found to exhibit limits of detection of below 1% RH (down to 50 ppm in nitrogen gas) with response and recovery times ranging from over one minute down to several seconds. The IPA sensor had response times under one minute, with an extrapolated detection limit of 0.02% v/v (160 ppm) IPA in water. This work also describes the spectroscopic properties of novel indicator compounds that are useful in chemical sensing (Part II). In particular, Chapter 5 describes the fabrication of unique starch/amylose-iodine composite films which demonstrate dramatic, humidity-sensitive colorimetric changes. Chapter 6 deals with the examination of the spectroscopic properties of a novel class of peripherally substituted porphyrazines that exhibit selective metal ion binding. Finally, Appendix C describes the use of a naphthalocyanine for the detection of tributylphosphate (TBP) in polar solution by visible absorbance spectroscopy.