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. 2020 Jun 24;11(6):611. doi: 10.3390/mi11060611

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© 2020 by the authors.

Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

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High-resolution and multiplex paper-based microfluidic analytical device. (a) Layers and fabrication steps of the high-resolution paper-based microfluidic device. (b) Color change of the indicators, i.e., bromothymol blue and bromocresol green, for a range of pH 4 to 10. (c,d) Calibration curves for determining pH of the solutions by two indicators, bromothymol blue (c) and bromocresol green (d) using CIExyY color space. (e) Images of a device with 256 detection zones after applying the pH 10 sample to the sample pad. Using the technical pen and pen plotter, the detection zones are automatically filled with bromothymol blue (R1) and methyl red (R2) pH indicators with any given arbitrary pattern. (f) Photograph of a device with 512 detection zones filled with bromothymol blue (R1) and methyl red (R2) pH indicators, after applying the pH 4 sample to the sample pad.