Droplet Microfluidics for Nucleic Acid Quantification and Single Cell Analysis

Abstract

Droplet microfluidics provides controlled generation of monodispersed droplets of the order of a few picoliters in multiphase microfluidic systems. These droplets are employed as micro-reactors to conduct chemical/biochemical reactions and assays in a controlled and high-throughput manner that find applications in point-of-care and lab-on-chip platforms. While the microfluidic devices are compact, the existing solutions to control fluid flow operations have a significant footprint that effects their portability, logistic viability and economics. As an alternate to the existing instrumentation-intensive flow-rate driven control for droplet generation, we studied and standardised suction driven fluid-flow control. In multiphase and multi-channel devices with suction-based flow control, microchannel geometry and suction pressure at the outlet determine the flow rates in individual channels. It is thus critical to understand the role of geometry along with suction pressure in the dynamics of droplet generation. We propose a governing parameter, called as modified capillary number, that captures droplet generation behaviour and outlines the design requirements for a suction driven droplet generation. As droplet microfluidics allows capture and analysis of individual cells with unprecedented control and throughput, single cell studies with microdroplets are gaining popularity. However, such analysis requires microfluidic devices with multiple unit operations that become a challenge with suction driven fluid-flow due to limited pressure head and lack of independent control over dispersed and continuous phase flow rates. To demonstrate single cell analysis, we defined and developed individual unit operations integrated in a multi-operation suction microfluidic device designed to quantify the low copy number RNA from single cells. The device, droplet digital Single cell Nucleic Acid Quantifier (dd-ScNAQ), successively performs encapsulation of single cells in droplets, cell lysis and cellular lysate/RNA distribution in...