Development of an Optofluidic Platform Based on Total Internal Reflection- Application of Dissolved Oxygen Sensing for Water Monitoring

Abstract

Water quality is of great importance to human as well as other forms of lives. The concentration of dissolved oxygen (DO) is one of the essential indicators for water quality. DO sensing has been widely used in many environmental applications such as natural water monitoring and waste water treatment. Three methods are currently used for DO measurement, namely titration, electrochemical and optical. In the optical method, DO is quantified by the reduction of fluorescence emission intensity of Ru based fluorophores through fluorescence quenching process. This optical method is compatible with autonomous DO monitoring while the titration method is not, and it has the advantages of faster response and higher sensitivity than the electrochemical method. These properties make the optical method suitable for surveillance of water quality over time as well as near real-time and high sensitivity detection of contaminations. In this thesis, we report the design, simulation, fabrication and characterization of a fluorescence quenching based DO sensing optofluidic device with the focus on sensitivity enhancement and cost/size reduction. In our method, DO detection sensitivity was improved by 4 folds through employing total-internal-reflection of the excitation light and optimizing the fluorophore film thickness in a multilayered microfluidic sensor structure. System cost and size were also reduced in this design.