Digital microfluidic chip merges multiple consecutive droplets (nl) selectively and controllably using surface acoustic waves.

The recent boom in single-cell omics has brought researchers one step closer to understanding the biological mechanisms associated with cell heterogeneity. Rare cells that have historically been obscured by bulk measurement techniques are being studied by single cell analysis and providing valuable insight into cell function. To support this progress, novel upstream capabilities are required for single cell preparation for analysis. Presented here is a droplet microfluidic, image-based single-cell sorting technique that is flexible and programmable. The automated system performs real-time dual-camera imaging (brightfield & fluorescent), processing, decision making and sorting verification. To demonstrate capabilities, the system was used to overcome the Poisson loading problem by sorting for droplets containing a single red blood cell with 85% purity. Furthermore, fluorescent imaging and machine learning was used to load single K562 cells amongst clusters based on their instantaneous size and circularity. The presented system aspires to replace manual cell handling techniques by translating expert knowledge into cell sorting automation via machine learning algorithms. This powerful technique finds application in the enrichment of single cells based on their micrographs for further downstream processing and analysis.

This review analyses state-of-the-art droplet control technologies that exhibit potential to be used in the new generation of screening devices.

This study presents a novel acoustic mixer comprising of a microfabricated silicon nitride membrane with a hole etched through it. We show that the introduction of the through hole leads to extremely fast and homogeneous mixing. When the membrane is immersed in fluid and subjected to acoustic excitation, a strong streaming field in the form of vortices is generated. The vortices are always observed to centre at the hole, pointing to the critical role it has on the streaming field. We hypothesise that the hole introduces a discontinuity to the boundary conditions of the membrane, leading to strong streaming vortices. With numerical simulations, we show that the hole's presence can increase the volume force responsible for driving the streaming field by 2 orders of magnitude, thus supporting our hypothesis. We investigate the mixing performance at different Peclet numbers by varying the flow rates for various devices containing circular, square and rectangular shaped holes of different dimensions. We demonstrate rapid mixing within 3 ms mixing time (90% mixing efficiency at 60 μl min⁻¹ total flow rate, Peclet number equals 8333 ± 3.5%) is possible with the current designs. Finally, we examine the membrane with two circular holes which are covered by air bubbles and compare it to when the membrane is fully immersed. We find that coupling between the holes' vortices occurs only when membrane is immersed; while with the bubble membrane, the upstream hole's vortices can act as a blockage to fluid flow passing it.

A microfluidic chip capable of steering and unevenly splitting plugs at a Y-junction uses surface acoustic waves.

Presented here is an automated microfluidic platform, pipette on a chip, capable of selectively pipetting subsamples from mobile droplets in the picoliter range with high accuracy using a non-contact approach. The system utilizes acoustic forces, is modular and robust allowing integration with existing lab on a chip devices.