In this study, paper-based microfluidic devices (μPADs) capable of K⁺ quantification in aqueous samples, as well as in human serum, using both colorimetric and distance-based methods are described. A lipophilic phase containing potassium ionophore I (valinomycin) was utilized to achieve highly selective quantification of K⁺ in the presence of Na⁺, Li⁺, and Mg²⁺ ions. Successful addition of a suspended lipophilic phase to a wax printed paper-based device is described and offers a solution to current approaches that rely on organic solvents, which damage wax barriers. The approach provides an avenue for future alkali/alkaline quantification utilizing μPADs. Colorimetric spot tests allowed for K⁺ quantification from 0.1–5.0 mM using only 3.00 μL of sample solution. Selective distance-based quantification required small sample volumes (6.00 μL) and gave responses sensitive enough to distinguish between 1.0 and 2.5 mM of sample K⁺. μPADs using distance-based methods were also capable of differentiating between 4.3 and 6.9 mM K⁺ in human serum samples. Distance-based methods required no digital analysis, electronic hardware, or pumps; any steps required for quantification could be carried out using the naked eye.

中文翻译：

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纸基微流体的基于距离的选择性K ⁺定量

在这项研究中，描述了能够使用比色法和基于距离的方法对水性样品以及人血清中的K ^+进行定量的纸基微流体装置（μPAD）。在Na ⁺，Li ⁺和Mg ²⁺离子存在的情况下，利用含有钾离子载体I（valinomycin）的亲脂相来实现对K ^+的高度选择性定量。描述了将悬浮的亲脂相成功添加到基于蜡的印刷纸基设备中，并为依赖有机溶剂破坏蜡壁的当前方法提供了解决方案。该方法为将来使用μPAD进行碱/碱定量提供了途径。K ⁺允许的比色斑点测试仅使用3.00μL样品溶液，可定量从0.1–5.0 mM。基于选择性距离的定量方法需要小样品量（6.00μL），并且给出的响应足够灵敏，可以区分1.0和2.5 mM的样品K ⁺。使用基于距离的方法的μPAD还能够区分人血清样品中的4.3和6.9 mM K ⁺。基于距离的方法不需要数字分析，电子硬件或泵；量化所需的任何步骤都可以使用肉眼进行。