Microdroplet-Based screening of freshwater green algae

Abstract

This thesis presents an integrated microfluidic platform for interactive single-cell screening of lipid-rich microalgae using droplet microfluidics. To achieve the efficient production of biofuels from algal biomass with economically viable process, selection and growing of highly productive lipid-rich algal strains should be preceded. Especially, the heterogeneity in the lipid accumulation among the individual cells in the same species should be monitored and investigated in a single cell level. Extraordinary advances in droplet microfluidics systems have been made on the basis of the development of droplet manipulation technology with encapsulation method in a single cell level. Monodispersed hydrogel microcapsules can be considered one of the microreactors which encapsulate a cell of interest by utilizing the droplet manipulation technology in a high-throughput manner, and are then transported downstream to allow the quantitative monitor the lipid accumulation of each alga. Also, microcapsules ensure the algal cell viability and capability of other analysis after determination. To guarantee the enhanced single-cell encapsulation efficiency, a new fluid introduction scheme with reduced particle adsorption was first proposed. This idea is based on a novel microparticle injection technique with lateral interconnection, which prevents particle loss, assisted by sample injection along the direction of fluid flow. Biological sample fluids, including fluorescent microparticles, and mammalian (U937) and green algae cells (Chlorella vulgaris), were injected directly via a through-hole drilled in the lateral direction, resulting in a significant reduction in microparticle attachment. It was confirmed that the proposed method accomplished a 100% enhancement of single-cell encapsulation compared to a Poisson distribution. At the high concentration (5×107 cells/mL) of C. vulgaris, the fraction of droplets containing single cells increased gradually from 28.67% to 40.00%...