Interactive droplet manipulation for microfluidic single-cell screening

Abstract

This thesis proposes a well-designed microfluidic system with hydrodynamic control of microdroplets can serve as a simple, feasible, and beneficial platform for biological assay. The selected experiment to assess practicability of pico to nanoliter microdroplet system is the assay for screening gene library inside Escherichia coli (E.coli). Cell-based screening is conventionally carried out in test tubes or well plates in which single cell isolation or reaction can be hardly achieved. The single-cell based assay platform requires the process of single-cell isolation, mixing with reagents for identifying certain gene expression, incubation with supplementary cell media, and recovery of the reacted cells for further analysis. This work proposed that microdroplets generated in two-phase fluid are the most compatible tool for single-cell isolation, and the method of secondary breakup of droplets to encapsulate single cells inside microdroplets is first introduced. The secondary breakup of droplet which is obtained from the conventional microchannel for droplet generation, into smaller sizes by simple integration of micro-groove structures or a pinched flow. While conventional microfluidic tool achieves single-cell isolation efficiency of less than 30%, droplets obtained from the secondary breakup collects about 50% of single-cell containing droplets, and the proportion of multiple-cell containing droplets are kept less than 16%. Mixing with reagents or supplementary cell media for droplet-based microfluidics requires merging events of droplets. Here we report the use of the abacus-groove structure for sequential addition of droplets. The abacus channel brings droplets together in a chamber with a control channel, which is analogous to biasing in electronics to change the pressure difference in the chamber and precisely determine the number of added droplets with no external forces integrated to the system other than syringe pumps. This method for droplet merging c...