Image analysis for a microfluidic paper-based analytical device using the CIE L☆a☆b☆ color system

The combination of a microfluidic paper-based analytical device (mu PAD) and digital image analysis is widely used for quantitative analysis with mu PADs because of its easy and simple operation. Herein, we have demonstrated a quantitative analysis based on multiple color changes on a mu PAD. The CIE L*a*b* color system was employed to analyse the digital images obtained with the mu PAD. We made pH measurements using a universal pH-indicator showing multiple color changes for various pH values of aqueous test solutions. The detectable pH range of this method was wider than the typical grayscale-based image analysis, and we succeeded in the measurements for a wide pH range of 2-9.