Morgan Blevins, S.M., 2021
Anna Michel, Advisor
In situ analysis of dissolved gas in surface waters is currently performed with large, expensive instruments, such as spectrometers, which are coupled with gas equilibration systems. Accurate, low cost, and portable sensors are needed to measure dissolved CH_4 and CO_2 concentrations in ecosystems to quantify their release and understand their relationship to the global carbon budget. At the same time, the ubiquity and consequences of microplastics in aqueous environments are just beginning to be recognized by the environmental research community. This thesis addresses the need for high quality and quantity environmental data to better study these aqueous pollutants. First, the design of the Low-Cost Gas Extraction and Measurement System (LC-GEMS) for dissolved CO_2 is presented. At just under $600 dollar to build, the LC-GEMS is an ultra-portable instrument for dissolved gas sensing in surface waters. Second, the novel designs of three planar nanophotonic and plasmonic structures as optical transducers for measuring dissolved CH_4 are presented. These designs are novel in the space of dissolved gas monitoring because they show potential to measure directly in the water phase while being robust and low-cost. Finally, this thesis presents a literature review and perspective to motivate the development of field-deployable microplastic sensing techniques.