Methods and systems are provided for serial femtosecond crystallography for reducing the vast amount of waste of injected crystals practiced with traditional continuous flow injections. A micrometer-scale 3-D printed water-in-oil droplet generator device includes an oil phase inlet channel, an aqueous phase inlet channel, a droplet flow outlet channel, and two embedded non-contact electrodes. The inlet and outlet channels are connected internally at a junction. The electrodes comprise gallium metal injected within the 3-D printed device. Voltage across the electrodes generates water-in-oil droplets, determines a rate for a series of droplets, or triggers a phase shift in the droplets. An external trigger generates the droplets based on the frequency of an XFEL utilized in droplet detection, thereby synchronizing a series of droplets with x-ray pulses for efficient crystal detection. The generated droplets can be coupled to an SFX with XFEL experiment compatible with common liquid injector such as a GDVN.