Electricity-free picoinjection assisted droplet microfluidics

Using droplet microfluidic picoinjection as a reactant dosing technique is of great importance in assembling artificial cells and performing multistep reactions. However, the utilization of electricity in the existing picoinjection complicates the device fabrication and operation, and compromises the bioactivity of the encapsulated bio-ingredients. In this work, we propose an electricity-free picoinjection technique as an alternative to address these issues. Specifically, by precisely controlling the pressures inside the microfluidic channel, we can inject one reactant into the flowing droplets that contain another reactant without applying the electric field. Furthermore, the dosed volumes can be tuned by controlling the value of external pressure or the ratio of flow rates between the continuous and droplet phases. To demonstrate the robustness of the proposed picoinjection, we apply it to synthesize crystals and nanoparticles. In the synthesis of crystals, the proposed picoinjection eliminates the problem of device fouling that occurs in the current reactant dosing devices. In the synthesis of nanoparticles, the proposed picoinjection generates nanoparticles that are highly monodispersed. As a result, this simplified picoinjection potentially extends the application of droplet microfluidics to investigate reaction dynamics or biochemical processes in cells. Besides, by eliminating the electricity, the proposed picoinjection avoids the usages of large equipment such as large power supplies or complicate devices, enhancing the accessibility of the proposed picoinjection.