Microfluidic train station: highly robust and multiplexable sorting of droplets on electric rails

Fluorescence-activated droplet sorting (FADS) has become a widely used technique for high-throughput screening applications. However, existing methods are very sensitive to fluctuating flow rates at the sorting junction, which can be caused by the pulsing effects of mechanical pumps, droplet aggregates or the accumulation of precipitates during lengthy biological screening applications. Furthermore, existing sorting devices allow only 2-way sorting. We present here a dielectrophoretic sorting system in which the droplets are sorted along multiple electrode pairs that run parallel to the channels. This enables highly reliable sorting (no errors were detected for more than 2000 sorting events) even when inverting the relative flow rates at a 2-way sorting junction from 80 : 20 to 20 : 80. Furthermore, our toolbox is scalable: we demonstrate on the example of a triple-colour sorting experiment with a total of four decoupled electrodes that multi-way sorting is feasible.