Single Cell Encapsulation Using a Droplet-Microfluidic Array

The traditional approach of studying cell-behavior involves performing bulk analysis capable of only average measurements of how an entire population of cells responds to external treatments. Results obtained from such analysis can often be inaccurate because they do not account for the behavior of individual cells that often times respond differently from other cells in a heterogeneous population. Droplet microfluidics is one way of bypassing the complications that arise from such cellular heterogeneity. In this project, we sought to design, fabricate and optimize a two-phase droplet microfluidic device capable of isolating individual cells in picoliter-sized droplets. The underlying principle of the device is to encapsulate cells in discrete aqueous droplets in a continuous oil phase. The droplet generators were fabricated using poly(dimethyl siloxane) (PDMS) by established soft lithography and PDMS replication techniques. The fluidic channels were treated using an Aquapel solution to alter the surface properties of the PDMS to make it more hydrophobic. Succeeding error correction, the flow rates of both the inlet aqueous and oil streams were optimized to continuously produce droplets of reliable size. Cell encapsulation rates were performed using HeLa cells to ensure single cell trapping in each droplet. Finally, the system was modified to include a droplet trapping array downstream of the flow focusing junction. The array was designed to trap the aqueous droplets by taking advantage of the difference in fluid densities and the surface tension of the drops to perform the time-dependent analysis of cellular behavior, an aspect of droplet microfluidics that is currently limited. The results presented here are the first step in the development of a new microfluidic platform capable of quantifying intracellular kinetics at multiple time points in intact single cells in a high throughput manner.