High-throughput injection with microfluidics using picoinjectors

Abstract

Adding reagents to drops is one of the most important functions in droplet-based microfluidic systems; however, a robust technique to accomplish this does not exist. Here, we introduce the picoinjector, a robust device to add controlled volumes of reagent using electromicrofluidics at kilohertz rates. It can also perform multiple injections for serial and combinatorial additions.electrocoalescence | high-throughput biology | in vitro compartmentalization

Picoinjection of Microfluidic Drops Without Metal Electrodes

“…To demonstrate the speed our method, we selectively injected droplets passing the injection site depending on the presence or absences of a fluorescent dye (Movie 1). Drops pass the injector at 200 Hz, though rates as high as 10 kHz are possible, depending on capabilities of the droplet detection mechanism 3 .…”

“…The electric field disrupts the arrangement of surfactant molecules on the interfaces of the drops, inducing a thin-film instability and triggering coalescence in emulsions that are otherwise stable 2 . Electrically-induced merging is also exploited in the design of the picoinjector, a device that injects reagents into drops as they flow past a pressurized channel 3 . To apply the electric field, picoinjector devices utilize metal electrodes, but the integration of metal electrodes into microfluidic chips is often a complex and error-prone process as the liquid-solder wires are easily compromised by air bubbles or dust and other debris in the channel, as well as fractures from stress or bending during device setup.…”

Synchronized reinjection and coalescence of droplets in microfluidics

“…1 The precise addition of reagents into the droplets is essential for this function. 20 Methods such as "picoinjection," where reagents contained in a pressurized channel are forced into re-injected target droplets under a controlled electric field, 2 are primarily useful for adding liquid reagents. It is more difficult to control the addition of small solid particles using such methods because of Poisson 25 fluctuations in the particle number.…”

Adding reagent to droplets with controlled rupture of encapsulated double emulsions

“…[10][11][12] Both employ electric fields to merge the contents of the target droplets with the reagent to be added. Because the target droplets join with the reagent while sharing the same carrier oil, it is possible for material to transfer between different target droplets.…”