Cell separation is one of the key limiting factors for precise analysis of non-axenic microbial lab cultures or environmental samples, and it remains a challenge to isolate target cells with high purity and viability via high-throughput cell sorting. During the past decade, hydrodynamic microfluidic platforms have attracted great attention in cell preparation for their high efficiency, robust performance and low cost. Here, we employ the use of a low-velocity sheath flow with high viscosity near the wall and a high-velocity sheath flow with low viscosity on the other side of the sample flow in a soft inertial separation chip. This not only prevents hard interactions between cells and chip walls but, in comparison to previous inertial separation methods, generates a significant increase in deflection of large cells while keeping the small ones in the original flow. We first conducted experiments on a mixture of small and large fluorescent particles (1.0 and 9.9 μm, respectively) and removed over 99% of the small particles. The separation efficiency was then tested on a culture of a bacterivorous jakobid flagellate, Seculamonas ecuadoriensis fed on the live bacterium, Klebsiella sp. Using our microfluidic chip, over 94% of live bacteria were removed while maintaining high jakobid cell viability. For comparison, we also conducted size-based cell sorting of the same culture using flow cytometry, which is widely used as a rapid and automated separation tool. Compared with the latter, our chip showed more than 40% higher separation efficiency. Thus, our device provides high purity and viability for cell separation of a sensitive cell sample (jakobid cells). Potentially, the method can be further used for applications in diagnostics, biological analyses and environmental assessment of mixed microbial samples.

中文翻译：

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基于陡峭速度梯度诱导的软惯性力的高纯度和活性细胞分离 jakobid 鞭毛虫†

细胞分离是对非无菌微生物实验室培养物或环境样品进行精确分析的关键限制因素之一，通过以下方法分离高纯度和活力的靶细胞仍然是一个挑战。高通量细胞分选。在过去的十年中，流体动力微流控平台以其高效、强大的性能和低成本在细胞制备中引起了极大的关注。在这里，我们在软惯性分离芯片中使用在壁附近具有高粘度的低速鞘流和在样品流的另一侧具有低粘度的高速鞘流。这不仅可以防止细胞和芯片壁之间的硬相互作用，而且与以前的惯性分离方法相比，大细胞的偏转显着增加，同时将小细胞保持在原始流动中。我们首先对大小荧光颗粒（分别为 1.0 和 9.9 μm）的混合物进行了实验，并去除了 99% 以上的小颗粒。Seculamonas ecuadoriensis以活细菌Klebsiella sp. 为食。使用我们的微流控芯片，超过 94% 的活细菌被去除，同时保持高 jakobid 细胞活力。为了比较，我们还使用流式细胞仪对同一培养物进行了基于大小的细胞分选，流式细胞仪被广泛用作快速和自动化的分离工具。与后者相比，我们的芯片的分离效率提高了 40% 以上。因此，我们的设备为敏感细胞样品（jakobid 细胞）的细胞分离提供了高纯度和活力。潜在地，该方法可进一步用于混合微生物样品的诊断、生物分析和环境评估中的应用。