Electro-generation of single femtoliter- and picoliter-volume aqueous droplets in microfluidic systems

This letter presents a new method to generate individual femtoliter- to picoliter-volume aqueous droplets in oil using single voltage pulses. With high-speed imaging, we characterized the displacement of the water-oil interface as a function of the time and amplitude of the voltage pulse. At high voltages where jetting and droplet formation occurred, we observed the ratio of droplet-to-jet diameter to be $\sim 1.84$ , which suggested Rayleigh instability as the primary mechanism responsible for droplet breakup. Droplets with volumes ranging from 14 fl to 8 pl were produced using this method.