Most biological fluids (such as blood, saliva, and lymph) in nature have certain viscoelasticity and are beginning to be used as the carrying fluids for viscoelastic microfluidics. However, the particle-focusing mechanisms in these new biological viscoelastic fluids are still unclear. In this work, the particle-focusing mechanisms in λ-DNA solutions were systematically explored. We first explored the particle focusing dynamics in a square cross-section under varied flow rates to uncover the effects of flow rate on particle focusing. Three focusing stages, from the classic five-position viscoelastic focusing to single-stream focusing and finally to multiplex-stream focusing, were clearly demonstrated. In addition, the particle focusing process along the channel length was demonstrated, and a first-fast-and-then-slow focusing process was clearly observed. Then, the effects of λ-DNA concentrations on particle focusing were explored and compared using the solutions with 0–25 ppm λ-DNA. Finally, we discussed the inferences of blockage ratio on particle focusing by changing the particle diameter and cross-sectional dimensions. Our work may provide a deeper understanding on the particle focusing mechanisms in biological viscoelastic fluids and lays a foundation for the subsequent particle counting and analysis and the development of low-cost portable flow cytometers.

中文翻译：

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直线微通道中流动的 λ-DNA 溶液中的粒子聚焦机制

自然界中的大多数生物流体（如血液、唾液、淋巴液）都具有一定的粘弹性，开始被用作粘弹性微流控的承载流体。然而，这些新的生物粘弹性流体中的粒子聚焦机制仍不清楚。在这项工作中，系统地探索了 λ-DNA 溶液中的粒子聚焦机制。我们首先探索了不同流速下方形横截面中的颗粒聚焦动力学，以揭示流速对颗粒聚焦的影响。清晰地展示了从经典的五位粘弹聚焦到单流聚焦，最后到多流聚焦的三个聚焦阶段。此外，还演示了沿通道长度的粒子聚焦过程，并清晰地观察到先快后慢的聚焦过程。然后，使用 0–25 ppm λ-DNA 的溶液探索并比较了 λ-DNA 浓度对粒子聚焦的影响。最后，我们讨论了通过改变颗粒直径和横截面尺寸，堵塞率对颗粒聚焦的影响。我们的工作可能会为生物粘弹性流体中的颗粒聚焦机制提供更深入的了解，并为后续的颗粒计数和分析以及低成本便携式流式细胞仪的开发奠定基础。