The wide spread of smartphones and QR codes for various end-user applications has had an impact beyond traditional fields of use, recently also reaching point-of-care testing (POCT). This work presents the integration of QR code recognition into paper-based analytical devices (PADs) with “distance-based” colorimetric signalling, resulting in semiquantitative readout fully relying on straightforward barcode reader solutions. PADs consist of an array of QR codes arranged in series inside a paperfluidic channel. A mask dye concept has been developed, which enables utilisation of colour changing indicators by initially hiding QR codes. The colour change of the indicator induced by the presence of an analyte of interest results in gradual unmasking of QR codes, which become recognisable by the smartphone barcode reader app. To reproducibly fabricate devices, all fabrication steps were performed by commercial desktop solid ink and inkjet printing. The QR code masking function was optimised by controlling the amount of printed mask dye through adjusting the opacity of printing patterns during the inkjet deposition process. For proof-of-concept, a model assay in the form of colorimetric copper ion (Cu²⁺) detection in the concentration range of 0.4 mM to 3.2 mM was evaluated. Consistent results independent of the smartphone model and environmental light condition were achieved with a free barcode reader app. To the best of our knowledge, this work is the first demonstration of a semiquantitative assay approach fully relying on QR code readout without digital colour analysis, customised app or hardware modification.

中文翻译：

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全打印的半定量纸质分析设备依靠QR码阵列读数。

智能手机和QR码在各种最终用户应用中的广泛使用已经对传统使用领域产生了影响，最近还达到了即时检验（POCT）。这项工作提出了将QR码识别与具有“基于距离”的比色信号的信号集成到基于纸张的分析设备（PAD）中的功能，从而完全依靠直接的条形码读取器解决方案进行半定量读取。PAD由一系列QR码组成，这些QR码在纸流通道内串联排列。已经开发出一种掩膜染料概念，该掩膜染料概念通过最初隐藏QR码来启用变色指示器。由感兴趣的分析物的存在引起的指示剂的颜色变化导致QR码逐渐暴露出来，QR码逐渐被智能手机条形码阅读器应用识别。为了可重复制造设备，所有制造步骤均通过商用台式固体墨水和喷墨印刷执行。通过调整喷墨沉积过程中印刷图案的不透明度来控制印刷的掩模染料的量，从而优化了QR码的掩模功能。为了进行概念验证，以比色铜离子（Cu评估了在0.4 mM至3.2 mM浓度范围内的²⁺）检测。通过免费的条形码读取器应用程序，可以获得与智能手机型号和环境光线条件无关的一致结果。据我们所知，这项工作是半定量分析方法的首次展示，该方法完全依靠QR码读数，而无需进行数字颜色分析，定制的应用程序或硬件修改。