Droplet merging is one of the key functions in the ever-widening applications of droplet microfluidics. Enhancing the efficiency of electric field-based droplet merging, namely electrocoalescence, can lead to an increase in platform stability and overcome one of the major bottlenecks in further improving throughputs of droplet microfluidic systems. In this work, a paired three-dimensional (3D) electrode design that can provide a uniform electric field within a droplet merging region, which is also properly aligned with the droplet dipole moments for highly efficient electrocoalescence is presented. A systematic study was conducted to compare the droplet merging performance of the presented 3D electrode design to other commonly used planar electrode, coplanar electrode, dual-coplanar electrode, and liquid metal 3D electrode designs. The presented 3D electrode design reduced the threshold input voltage required to obtain droplet fusion by up to 75 %. In addition, a droplet merging efficiency of higher than 95 % was consistently observed, compared to less than 85 % merging efficiency for the conventionally used electrode designs. We expect that this droplet electrocoalescence design will improve the overall throughput and merging success rate in droplet microfluidic based high-throughput assays.
Droplet microfluidics Droplet merging Droplet electrocoalescence 3D electrode
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This work was supported by the National Science Foundation (NSF) Emerging Frontiers in Research and Innovation (EFRI) grant EFRI#1240478 and the Defense Threat Reduction Agency (DTRA) grant HDTRA12-1-0028.
A 3D copper electrode electrocoalescence video (conducted intentionally at low speed for high-resolution droplet visualization purposes). (MPEG 4160 kb)