(175at) A Triple-Input Microfluidic Droplet Trapping Array for Multiplexed Single Cell Analysis

Authors: 
Bajgiran, K. R., Louisiana State University
Elkhanoufi, R., Louisiana State University
Dorman, J. A., Louisiana State University
Melvin, A. T., Louisiana State University
An evolving technology to control the cellular environment utilizes the principles of droplet-based microfluidics, where an aqueous flow is segregated into individual droplets within an immiscible carrier fluid to encapsulate cells, organic molecules and reagents. Droplet microfluidic devices offer a wide-range of applications such as high-throughput drug screening, rare cell detection, and single cell DNA amplification. While droplet microfluidic devices have numerous applications, they are oftentimes limited to a single input condition that prevents them from being able to analyze multiple input parameters (e.g., combinations of cellular treatments) in a single experiment. Previous work from our group demonstrated the feasibility of utilizing photoluminescent rare earth (RE)-doped nanoparticles (NPs) as optical tags for simultaneous droplet tracking as a method to identify droplets generated from different input conditions. Similarly, we demonstrated the utility of a microfluidic droplet trapping array capable of generating 70 µm aqueous droplet in a 775member array with ~40-50% single cell trapping efficiency. The goal of this work is to expand upon the previous studies by fabricating a triple-input microfluidic droplet trapping array capable of high-throughput single cell analysis. The multi-input microfluidic device incorporates four input streams: one continuous oil inlet (containing 2% w/w fluorosurfactant) and three aqueous inlets each of which contains three different samples with three different RE-doped NPs. Each of the three aqueous inlets intersects with the oil channel at three T-junctions positioned in series upstream of a large overhead trapping array to collect single droplet for on-chip interrogation and analysis. This device utilized gravity-induced flow for droplet generation to reduce the number of syringe pumps needed to operate the system. In order to determine optimal operating parameters, a combination of mathematical modeling and experimental studies of the fluid properties were performed to investigate the effect of the capillary number (Ca), the channel geometry (cross section aspect ratio­), and the flow rate (disperse-to-continuous phases) ratio on the dynamics of the droplet breakup. The spacing between the three T-junctions and the dimensions of the device were further optimized using COMSOL Multiphysics to ensure rapid and monodisperse droplet generation. The downstream trapping array has a capacity for isolating ~3500 droplets, which are separated from the bulk solution due to the difference in densities between the aqueous and oil phases. This array allows for time-dependent single cell analysis without the need for expensive high-speed cameras. The work described here is a first step towards a fully characterized, multi-input microfluidic droplet trapping device capable of performing high-throughput screening of individual cellular behavior under a variety of cancer therapeutics simultaneously in a time and cost efficient manner.