Synchronized reinjection and coalescence of droplets in microfluidics

• Published in: Lab on a chip Vol. 14; no. 3; pp. 509 - 513
• Main Authors: Lee, Manhee, Collins, Jesse W, Aubrecht, Donald M, Sperling, Ralph A, Solomon, Laura, Ha, Jong-Wook, Yi, Gi-Ra, Weitz, David A, Manoharan, Vinothan N
• Format: Journal Article
• Language: English
• Published: England 07.02.2014
• Subjects: Coalescence; Hydrostatic Pressure; Microfluidics - instrumentation; Microfluidics - methods; Oils - chemistry; Surface-Active Agents - chemistry; Water - chemistry
• ISSN: 1473-0197; 1473-0189
• DOI: 10.1039/c3lc51214b

Coalescence of two kinds of pre-processed droplets is necessary to perform chemical and biological assays in droplet-based microfluidics. However, a robust technique to accomplish this does not exist. Here we present a microfluidic device to synchronize the reinjection of two different kinds of droplets and coalesce them, using hydrostatic pressure in conjunction with a conventional syringe pump. We use a device consisting of two opposing T-junctions for reinjecting two kinds of droplets and control the flows of the droplets by applying gravity-driven hydrostatic pressure. The hydrostatic-pressure operation facilitates balancing the droplet reinjection rates and allows us to synchronize the reinjection. Furthermore, we present a simple but robust module to coalesce two droplets that sequentially come into the module, regardless of their arrival times. These re-injection and coalescence techniques might be used in lab-on-chip applications requiring droplets with controlled numbers of solid materials, which can be made by coalescing two pre-processed droplets that are formed and sorted in devices.