Department of Mechanical Engineering, National Taiwan University of Science and Technology, Taipei, 106, Taiwan.
Sci Rep. 2021 Nov 2;11(1):21496. doi: 10.1038/s41598-021-01048-1.
One of the main objectives of microfluidic paper-based analytical devices is to present solutions particularly, for applications in low-resource settings. Therefore, screen-printing appears to be an attractive fabrication technique in the field, due to its overall simplicity, affordability, and high-scalability potential. Conversely, the minimum feature size attained using screen-printing is still rather low, especially compared to other fabrication methods, mainly attributed to the over-penetration of hydrophobic agents, underneath defined patterns on masks, into the fiber matrix of paper substrates. In this work, we propose the use of the over-penetration to our advantage, whereby an appropriate combination of hydrophobic agent temperature and substrate thickness, allows for the proper control of channel patterning, rendering considerably higher resolutions than prior arts. The implementation of Xuan paper and nail oil as novel substrate and hydrophobic agent, respectively, is proposed in this work. Under optimum conditions of temperature and substrate thickness, the resolution of the screen-printing method was pushed up to 97.83 ± 16.34 μm of channel width with acceptable repeatability. It was also found that a trade-off exists between achieving considerably high channel resolutions and maintaining high levels of repeatability of the process. Lastly, miniaturized microfluidic channels were successfully patterned on pH strips for colorimetric pH measurement, demonstrating its advantage on negligible sample-volume consumption in nano-liter range during chemical measurement and minimal interference on manipulation of precious samples, which for the first time, is realized on screen-printed microfluidic paper-based analytical devices.
微流控纸基分析器件的主要目标之一是提供解决方案，特别是针对资源有限环境中的应用。因此，丝网印刷在该领域似乎是一种有吸引力的制造技术，因为它具有总体简单、经济实惠和高可扩展性的潜力。然而，与其他制造方法相比，丝网印刷达到的最小特征尺寸仍然相当低，这主要归因于疏水剂在掩模定义图案下过度渗透到纸基纤维基质中。在这项工作中，我们利用这种过度渗透的优势，通过适当组合疏水剂温度和基底厚度，可以对通道图案进行精确控制，从而实现比以前的技术更高的分辨率。本工作提出使用宣纸和指甲油分别作为新型基底和疏水剂。在温度和基底厚度的最佳条件下，丝网印刷方法的分辨率提高到 97.83±16.34μm 的通道宽度，具有可接受的重复性。还发现，在实现相当高的通道分辨率和保持过程的高重复性之间存在权衡。最后，成功地在 pH 试纸上对微型微流控通道进行图案化，用于比色 pH 测量，展示了其在纳米升范围内进行化学测量时消耗的样本量极小，以及对珍贵样本操作干扰极小的优势，这是首次在丝网印刷微流控纸基分析器件上实现。
