Microfluidic Devices for Neural and Behavioral Screening of C.Elegans using Electric Field

C. elegans is an invaluable model for studying human diseases, from understanding disease pathology to screening for chemicals toxicity and therapeutic effects. However, technological deficiencies in achieving automated, fast, simple, and low-cost C. elegans-based screening assays have hindered the widespread use of this organism in the gene screening, toxicology and chemical screening areas. Various microfluidics and lab-on-a-chip systems have been reported for precise control and quantification of different sensory-motor processes of C. elegans such as electrotaxis, i.e., response to the electric field (EF) by swimming towards the negative electrode in a polarized system like a microchannel. The current electrotaxis microfluidic devices have a large footprint, low-throughput, and are slow due to their dependency on gait behaviours in terms of speed, body bend frequency, and reorientation. On-chip neuronal imaging has not been incorporated for the correlation of electrotaxis deficiency with neurodegeneration. Moreover, up until now, most of the electrotaxis assays have been conducted by exposing the entire worm to EF and were limited to gait behaviours, giving less attention to understanding C. elegans electrosensation and behaviours other than electrotaxis. Therefore, this thesis aimed to enhance our understanding of C. elegans electrosensation and the effects of EF on different phenotypes using microfluidic devices with enhanced behavioral throughputs. In Objective 1 of the thesis, we increased the number of worms that could be electrotactically tested and fluorescently imaged simultaneously, achieving a behavioral throughput of at least 9 worms every 5 minutes, which has not been achieved previously for electrically induced behavioral assays even with automated systems. In Objective 2, the electrotaxis response of semi-mobile worms was introduced to provide an assay inside a more confined area and study whether selective exposure of the worms head or tail to EF results in a directional electrotaxis. Interestingly, the results indicated the involvement of the vulva neurons in electrotaxis, which implied that the head neurons are not solely responsible for electrotaxis. Since vulva neurons showed involvement in C. elegans electrosensation, in Objective 3, we introduced, for the first time, a novel on-demand EF-evoked behaviour, termed electric egg-laying, in a simple to use microfluidic device that enabled trapping and exposure of individual worms to controlled EF conditions. Interestingly, we found that egg-laying is EF polarity dependent with a significant increase in the egg-count for anode-facing worms. Lastly, in Objective 4, we enhanced the behavioral throughput of our electric egg-laying assay while allowing on-chip fluorescent imaging and showed the technique's effectiveness for toxicity assessment. As a proof of concept, we used genetically and chemically induced models of Parkinson's disease as well as microplastics toxicity for showing the applicability of our techniques for behavioural and neuronal screening. A significant advantage offered by our devices was their ability to keep the identity of a worm known throughout an assay, which enabled correlating the chemical uptake heterogeneity with neuron degeneration and behavioral outputs at a single-worm resolution. It is anticipated that these microfluidic devices will play a major role in facilitating a fundamental understanding of C. elegans electrosensation, disease investigations, and chemical screening and toxicity assays.