We propose the use of water-based alkyl ketene dimer (AKD) ink for fast and user-friendly patterning of paper microfluidic devices either manually or using an inexpensive XY-plotter. The ink was produced by dissolving hydrophobic AKD in chloroform and emulsifying the solution in water. The emulsification was performed in a warm water bath, which led to an increased rate of the evaporation of chloroform. Subsequent cooling led to the final product, an aqueous suspension of fine AKD particles. The effects of surfactant and AKD concentrations, emulsification procedure, and cooling approach on final ink properties are presented, along with an optimized protocol for its formulation. This hydrophobic agent was applied onto paper using a plotter pen, after which the paper was heated to allow spreading of AKD molecules and chemical bonding with cellulose. A paper surface patterned with the ink (10 g L-1 AKD) yielded a contact angle of 135.6° for water. Unlike organic solvent-based solutions of AKD, this AKD ink does not require a fume hood for its use. Moreover, it is compatible with plastic patterning tools, due to the effective removal of chloroform in the production process to less than 2% of the total volume. Furthermore, this water-based ink is easy to prepare and use. Finally, the AKD ink can also be used for the fabrication of so-called selectively permeable barriers for use in paper microfluidic networks. These are barriers that stop the flow of water through paper, but are permeable to solvents with lower surface energies. We applied the AKD ink to confine and preconcentrate sample on paper, and demonstrated the use of this approach to achieve higher detection sensitivities in paper spray ionization-mass spectrometry (PSI-MS). Our patterning approach can be employed outside of the analytical lab or machine workshop for fast prototyping and small-scale production of paper-based analytical tools, for use in limited-resource labs or in the field.

中文翻译：

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用于纸张微流体中用户友好图案的水性烷基乙烯酮二聚体墨水

我们建议使用水性烷基乙烯酮二聚体 (AKD) 墨水手动或使用廉价的 XY 绘图仪快速且用户友好地对纸微流体设备进行图案化。油墨是通过将疏水性 AKD 溶解在氯仿中并在水中乳化该溶液而制成的。乳化在温水浴中进行，这导致氯仿蒸发速率增加。随后的冷却导致最终产品，AKD 细颗粒的水悬浮液。介绍了表面活性剂和 AKD 浓度、乳化程序和冷却方法对最终油墨性能的影响，以及其配方的优化方案。使用绘图笔将这种疏水剂涂在纸上，然后加热纸以允许 AKD 分子扩散并与纤维素进行化学键合。用油墨 (10 g L-1 AKD) 图案化的纸表面对水产生 135.6° 的接触角。与基于有机溶剂的 AKD 溶液不同，这种 AKD 墨水不需要通风橱即可使用。此外，由于在生产过程中有效去除氯仿至总体积的 2% 以下，因此它与塑料图案化工具兼容。此外，这种水性油墨易于制备和使用。最后，AKD 墨水还可用于制造所谓的选择性渗透屏障，用于纸微流体网络。这些是阻止水流过纸张的屏障，但可渗透表面能较低的溶剂。我们使用 AKD 墨水将样品限制和预浓缩在纸上，并证明了使用这种方法在纸喷雾电离质谱 (PSI-MS) 中实现更高的检测灵敏度。我们的图案化方法可用于分析实验室或机器车间之外的快速原型制作和纸质分析工具的小规模生产，用于资源有限的实验室或现场。