Observed velocity fluctuations in monodisperse droplet generators.

On-chip monodisperse droplet generation and analysis is ideal for low concentration and single molecule applications because it enables reagents to be partitioned into identical nanoliter or smaller reactor volumes while allowing real-time optical interrogation. Typically, these systems operate in a continuous droplet generation mode to maximize sample throughput. We have observed that on-chip droplet production for water-in-oil emulsions causes downstream droplet velocity fluctuations similar to those reported for gas-in-liquid emulsion systems with a periodicity equivalent to the droplet generation rate. This phenomenon can affect the accuracy of data collection due to variation in photon integration times as the moving droplets are observed. Here we perform high speed imaging and frequency domain analysis to describe the periodic velocity fluctuations due to monodisperse droplet generation.