Development of Optofluidic Sensors for Remote Monitoring Applications

Abstract

In this dissertation fluorescence-based sensors for dissolved gases were developed for remote health monitoring applications including urine analysis. Detection of dissolved gases demonstrate diagnostic potential in body fluids, and indicate the metabolism of microorganisms driven by contaminated water. The emphasis of this research was on optimizing the sensitivity of fluorescence-based fluid sensing systems by configuring key design parameters towards cost reduction. A review of urine analysis indicated several methods for imaging, particle analysis, and detection of dissolved analytes. The review encourages readers to consider integrating sensing systems to provide additional context to results. An optical Dissolved Oxygen (DO) sensor was reproduced using phosphorescent organometallic dyes. The sensitivity of the DO sensor was experimentally optimized by employing Total Internal Reflection (TIR) of excitation light within the multilayered device by controlling the incident angle and sensitive film thickness. Novel 3D ray tracing-based computer models were developed based on the experimental results to explain the sensitivity enhancement mechanism of TIR. The path of light within the device and fluorescence generation sites were visualized and relative sensitivity was predicted. The model was validated by comparison with experimental results and expanded to predict the relative sensitivity of devices using different coupling strategies. This new optical model enables researchers to select an optimal coupling and detection scheme given their unique sensor design and application. A fluorescence based optofluidic sensor for Ammonia was redesigned based on experiment and simulation results. An optofluidic chip reader was produced to measure fluorescence sensors using low cost consumer electronics. The sensitivity of the ammonia sensor module has not been demonstrated; however, identified design challenges will be overcome in future efforts. As a result of this research, the cost of optofluidic sensing systems may be reduced towards enabling widely deployed remote monitoring networks for health and water quality.