Programmable microfluidic platform for spatiotemporal control over nanoliter droplets

Droplet microfluidics offers an effective way for compartmentalizing samples and reagents for various biological and/or biochemical assays. However, an active control over size and frequency of individual droplets is quite difficult to achieve with off-chip pumping mechanisms such as syringe pumps. In this article, we propose the use of programmable microfluidic architectural components for spatiotemporal droplet control. On-chip three-valve diaphragm pumps were used to drive both dispersed and carrier phases toward a microfluidic T-junction. Individual droplet sizes and spacings were varied by controlling the number of pump cycles for injection and break-off. Droplet generation frequency was modulated by adjusting valve actuation rate. Droplet sizes were quantified for various pump parameters to identify the parametric space for stable and reliable droplet generation. Complex droplet trains with variable drop sizes and spacing were created by programming the desired pump states. Combinatorial merging and mixing of two droplets in various volumetric ratios was performed in a divergent mixing geometry to demonstrate utility of this technology.