A wide range of microfluidic paper-based analytical devices (μPADs) have been developed in the last decade. Despite this, the quality of colorimetric analysis has not substantially improved as the data is vulnerable to heterogeneous color distribution (e.g., coffee ring effects), non-uniform shapes of colored detection area, and noise from the underlying paper structure. These limitations are here addressed by a colorimetric method to quantify freely discharged dye on paper substrate, without the need for a defined channel or hydrophobic barrier. For accurate quantification, colorimetric absorbance values are calculated for each pixel based on the recorded RGB values and noise from the paper structure eliminated, to extract accurate absorbance information at the pixel level. Total analyte quantity is then calculated through the conversion of absorbance values into quantity values for each pixel followed by integration across the entire image. The resulting quantity is shown to be independent of the shape of the applied colored dye spot, with a cross, circle or rod shape all giving the same quantity information. The approach is applied to a capillary-based potassium-selective sensor, where the sample solution is loaded with the dye thioflavin T (ThT) obtained by quantitative exchange with K⁺ in a sensing capillary, which is discharged onto a bare paper substrate without any channels. The resulting dye quantity is successfully obtained by flatbed scanner and smartphone. The successful automated computation of colorimetric data on μPADs will help realize simpler paper-based assay and reaction systems that should be more applicable to addressing real world analytical problems.

中文翻译：

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纸质分析仪上的比色吸收图和定量。

在过去的十年中，已经开发出了多种基于纸的微流体分析设备（μPAD）。尽管如此，由于数据容易受到异类颜色分布（例如，，咖啡环效果），彩色检测区域的形状不均匀以及底层纸张结构产生的噪音。这些限制可通过比色法解决，以定量确定纸基上自由排放的染料，而无需定义通道或疏水屏障。为了精确定量，根据记录的RGB值和消除的纸张结构中的噪声为每个像素计算比色吸收值，以提取像素级别的准确吸收信息。然后，通过将吸光度值转换为每个像素的数量值，然后对整个图像进行积分来计算总分析物数量。显示的结果数量与所施加的有色染料斑点的形状无关，带有叉号，圆形或棒形都给出相同的数量信息。该方法适用于基于毛细管的钾选择性传感器，其中样品溶液中装有通过与K定量交换而获得的染料硫代黄素T（ThT）⁺在感应毛细管中，该毛细管被排放到没有任何通道的裸纸基材上。通过平板扫描仪和智能手机成功获得了最终的染料量。在μPAD上成功完成比色数据的自动计算，将有助于实现更简单的基于纸张的测定和反应系统，该系统应更适用于解决现实世界中的分析问题。