Novel on-demand droplet generation for selective fluid sample extraction

Abstract

A novel microfluidic device enabling selective generation of droplets and encapsulation of targets is presented. Unlike conventional methods, the presented mechanism generates droplets with unique selectivity by utilizing a K-junction design. The K-junction is a modified version of the classic T-junction with an added leg that serves as the exit channel for waste. The dispersed phase fluid enters from one diagonal of the K and exits the other diagonal while the continuous phase travels in the straight leg of the K. The intersection forms an interface that allows the dispersed phase to be controllably injected through actuation of an elastomer membrane located above the inlet channel near the interface. We have characterized two critical components in controlling the droplet size-membrane actuation pressure and timing as well as identified the region of fluid in which the droplet will be formed. This scheme will have applications in fluid sampling processes and selective encapsulation of materials. Selective encapsulation of a single cell from the dispersed phase fluid is demonstrated as an example of functionality of this design.

Programmable active droplet generation enabled by integrated pneumatic micropumps

“…38 Pneumatic valves fabricated by soft lithography have been demonstrated to be a promising technique for controlled droplet forma-tion. 18,[31][32][33] An advantage of this approach is its inherent amenability with large-scale microfluidic integration and automation. However, current valve-based methods rely on using external pumps to continuously flow the dispersed phase while actuating the integrated valves to modulate the passive droplet formation in microchannels.…”

“…30 As droplet microfluidics evolves, precise and controllable droplet generation has been recognized as an important component in developing droplet-based platforms for biological and medical applications. Droplet formation not only directly impacts on the performance of stochastic or ondemand droplet partition of targets, 20,31 but also influences the downstream droplet manipulation, such as selective pairing and fusion. [32][33][34][35] A variety of methods based on different mechanisms have been investigated to achieve controllable and eventually programmable droplet formation.…”

K-Channel: A Multifunctional Architecture for Dynamically Reconfigurable Sample Processing in Droplet Microfluidics

“…Lin, et al used a cross-channel flow of a cell suspension past an oil channel to generate single cell-containing droplets-on-demand (DoD) upon nearby PDMS valve triggering. 41 This structure stably maintained the aqueous cell suspension-oil interface before and after valve actuation. More recently, a similar approach adapted a cross-channel structure which dispersed flow instabilities through the cross-channel to improve droplet formation reproducibility.…”

On demand nanoliter-scale microfluidic droplet generation, injection, and mixing using a passive microfluidic device

“…To select the valves, usually more air-pressure channels are required per nozzle. 21 In addition to these static DoD systems, dynamic creation of DoDs 22 uses the surface tension between the sample and the carrier-fluid, typically water in oil, to pinch off a droplet with a sudden-pressure impulse on the built-in valve, but the reported sensitivity of the interface makes it unlikely that this principle may be used for more than one or two nozzles in the same microfluidic flow system.…”