Siedlik Michael J, Issadore David
Department of Bioengineering, University of Pennsylvania, Philadelphia, PA 19104 United States.
Department of Electrical and Systems Engineering, University of Pennsylvania, Philadelphia, PA 19104 United States.
Microsyst Nanoeng. 2022 Apr 29;8:46. doi: 10.1038/s41378-022-00381-3. eCollection 2022.
Droplet microfluidics is based on a toolbox of several established unit operations, including droplet generation, incubation, mixing, pico-injection, and sorting. In the last two decades, the development of droplet microfluidic systems, which incorporate these multiple unit operations into a workflow, has demonstrated unique capabilities in fields ranging from single-cell transcriptomic analyses to materials optimization. One unit operation that is sorely underdeveloped in droplet microfluidics is washing, exchange of the fluid in a droplet with a different fluid. Here, we demonstrate what we name the "pico-washer," a unit operation capable of simultaneously adding fluid to and removing fluid from droplets in flow while requiring only a small footprint on a microfluidic chip. We describe the fabrication strategy, device architecture, and process parameters required for stable operation of this technology, which is capable of operating with kHz droplet throughput. Furthermore, we provide an image processing workflow to characterize the washing process with microsecond and micrometer resolution. Finally, we demonstrate the potential for integrated droplet workflows by arranging two of these unit operations in series with a droplet generator, describe a design rule for stable operation of the pico-washer when integrated into a system, and validate this design rule experimentally. We anticipate that this technology will contribute to continued development of the droplet microfluidics toolbox and the realization of novel droplet-based, multistep biological and chemical assays.
液滴微流控技术基于一系列既定的单元操作工具箱，包括液滴生成、孵育、混合、皮升注射和分选。在过去的二十年中，将这些多个单元操作整合到一个工作流程中的液滴微流控系统的发展，已在从单细胞转录组分析到材料优化等领域展现出独特的能力。在液滴微流控中严重未得到充分发展的一个单元操作是洗涤，即将液滴中的流体与另一种不同的流体进行交换。在此，我们展示了我们所称的“皮升洗涤器”，这是一种能够在流动过程中同时向液滴中添加流体和从液滴中去除流体的单元操作，而在微流控芯片上仅需占用很小的空间。我们描述了该技术稳定运行所需的制造策略、器件架构和工艺参数，该技术能够以千赫兹的液滴通量运行。此外，我们提供了一种图像处理工作流程，以微秒和微米分辨率表征洗涤过程。最后，我们通过将其中两个单元操作与液滴发生器串联排列来展示集成液滴工作流程的潜力，描述了将皮升洗涤器集成到系统中时稳定运行的设计规则，并通过实验验证了该设计规则。我们预计这项技术将有助于液滴微流控工具箱的持续发展以及新型基于液滴的多步生物和化学分析的实现。
