Quantitative Analysis of Colorimetric Hydrogel/Paper Mini-Disk Arrays with a Handheld Wi-Fi Scanner

Abstract

Traditional quantitative colorimetric assays often rely on bulky laboratory instruments, such as UV-Vis spectrophotometers or microplate readers. While smartphone-based point-of-need (PON) tools have emerged as alternatives, they are frequently limited by ambient lighting variation and perspective distortion. To address these challenges, we developed a PON quantitative platform for colorimetric assays that integrates hydrogel (agarose based) coated filter paper as reaction "mini-disks", a handheld Wi-Fi scanner as the imaging tool, and a custom-designed app (universal for both smartphones and pads) for color analysis. Using two representative colorimetric assays, pH-differential colorimetry for anthocyanin and Ellman's assay for parathion methyl, we validated the performance of this new Wi-Fi scanning platform with conventional UV-Vis spectrophotometry analysis. The results demonstrate that this integrated Wi-Fi scanning protocol promises as a reliable, universal, low-cost, and convenient tool for on-site, quantitative colorimetric analysis in resource-limited settings.