Kielpinski Mark, Walther Oliver, Cao Jialan, Henkel Thomas, Köhler J Michael, Groß G Alexander
Microfluidics Group, Institute for Photonic Technologies, IPHT-Jena, Albert-Einstein-Str. 9, Jena 07745, Germany.
Department of Physical Chemistry and Microreaction Technologies, Institute of Chemistry and Biotechnology, Technische Universität Ilmenau, Prof.-Schmidt-Straße 26, Ilmenau 98693, Germany.
Micromachines (Basel). 2020 Apr 10;11(4):394. doi: 10.3390/mi11040394.
The defined formation and expansion of droplets are essential operations for droplet-based screening assays. The volumetric expansion of droplets causes a dilution of the ingredients. Dilution is required for the generation of concentration graduation which is mandatory for many different assay protocols. Here, we describe the design of a microfluidic operation unit based on a bypassed chamber and its operation modes. The different operation modes enable the defined formation of sub-µL droplets on the one hand and the expansion of low nL to sub-µL droplets by controlled coalescence on the other. In this way the chamber acts as fluidic interface between two fluidic network parts dimensioned for different droplet volumes. Hence, channel confined droplets of about 30-40 nL from the first network part were expanded to cannel confined droplets of about 500 to about 2500 nL in the second network part. Four different operation modes were realized: (a) flow rate independent droplet formation in a self-controlled way caused by the bypassed chamber design, (b) single droplet expansion mode, (c) multiple droplet expansion mode, and (d) multiple droplet coalescence mode. The last mode was used for the automated coalescence of 12 droplets of about 40 nL volume to produce a highly ordered output sequence with individual droplet volumes of about 500 nL volume. The experimental investigation confirmed a high tolerance of the developed chamber against the variation of key parameters of the dispersed-phase like salt content, pH value and fluid viscosity. The presented fluidic chamber provides a solution for the problem of bridging different droplet volumes in a fluidic network.
液滴的精确形成和扩展是基于液滴的筛选分析的关键操作。液滴的体积膨胀会导致成分稀释。许多不同的分析方案都需要通过稀释来产生浓度梯度。在此，我们描述了一种基于旁路腔室的微流控操作单元的设计及其操作模式。一方面，不同的操作模式能够精确形成亚微升液滴，另一方面，通过可控聚并可将低纳升液滴扩展至亚微升液滴。这样，该腔室就充当了两个针对不同液滴体积设计的流体网络部分之间的流体界面。因此，来自第一网络部分的约30 - 40纳升的通道受限液滴在第二网络部分被扩展为约500至约2500纳升的通道受限液滴。实现了四种不同的操作模式：(a) 由旁路腔室设计以自控方式实现与流速无关的液滴形成，(b) 单液滴扩展模式，(c) 多液滴扩展模式，以及(d) 多液滴聚并模式。最后一种模式用于将12个约40纳升体积的液滴自动聚并，以产生具有约500纳升个体液滴体积的高度有序输出序列。实验研究证实，所开发的腔室对分散相的关键参数（如盐含量、pH值和流体粘度）的变化具有很高的耐受性。所展示的流体腔室为解决流体网络中不同液滴体积的衔接问题提供了一种解决方案。
