Department of Electrical and Computer Engineering, Texas A&M University, College Station, USA.
Department of Electrical and Computer Engineering, Texas A&M University, College Station, USA; Department of Biomedical Engineering, Texas A&M University, College Station, USA.
Biosens Bioelectron. 2017 Nov 15;97:41-45. doi: 10.1016/j.bios.2017.05.036. Epub 2017 May 21.
Concentrating cells or adjusting the concentration of cells are one of the most fundamental steps in cell biology experiments, and are typically achieved through centrifugation. However this step is challenging to implement in droplet microfluidics. Here we present an in-droplet cell concentrator that operates by first gradually focusing cells inside a droplet to one side of the droplet using negative dielectrophoresis (nDEP), followed by asymmetric droplet splitting using a Y-shaped junction, resulting in two daughter droplets, one of which containing all or most of the cells. The developed platform was first characterized using droplets containing different number of polystyrene (PS) particles and by varying the applied voltages, flow rates, and the width ratios of the droplet splitting microchannels. Using this platform, the volume of one daughter droplet could be reduced up to 84% compared to that of the mother droplet, which resulted in the PS particle concentration to increase by 5.6-fold, with an average recovery rate of 90%. When testing with cells (Chlamydomonas reinhardtii), recovery rates as high as 98% could be achieved while increasing the cell concentration by 5-fold. This technology adds a new capability to droplet microfluidics operation, and can be used for adjusting concentrations of cells in droplets, exchanging solutions in which cells are suspended in droplets (including cell washing steps), and separating cells of different dielectric properties inside droplets, all of which are common steps in conventional cell assays but have been so far difficult to achieve in droplet format.
浓缩细胞或调整细胞浓度是细胞生物学实验中最基本的步骤之一，通常通过离心来实现。然而，这一步在液滴微流控中具有挑战性。在这里，我们提出了一种在液滴内的细胞浓缩器，它通过首先使用负介电泳（nDEP）将细胞逐渐聚焦到液滴的一侧来实现，然后使用 Y 形结进行不对称液滴分裂，从而产生两个子液滴，其中一个子液滴包含全部或大部分细胞。该开发平台首先使用含有不同数量聚苯乙烯（PS）颗粒的液滴和不同的施加电压、流速以及液滴分裂微通道的宽度比进行了表征。使用此平台，与母液滴相比，一个子液滴的体积可减少高达 84％，从而导致 PS 颗粒浓度增加 5.6 倍，平均回收率为 90％。在用细胞（莱茵衣藻）进行测试时，回收率高达 98％，同时将细胞浓度提高 5 倍。这项技术为液滴微流控操作增加了新的功能，可用于调整液滴中细胞的浓度、交换细胞悬浮在液滴中的溶液（包括细胞洗涤步骤）以及分离液滴内具有不同介电性质的细胞，所有这些都是常规细胞测定中的常见步骤，但迄今为止很难在液滴格式中实现。
