A chemically functionalized paper-based microfluidic platform for multiplex heavy metal detection

This study presents a simple, fast, and sensitive method for multiplexing heavy metal detection. Using a chemically patterned microfluidic paper-based analytical device (C-PAD), silane compounds terminating in amine (NH2), carboxyl (COOH), and thiol (SH) were immobilized on a patterned chromatography paper via condensation reactions. Three chromogenic reagents that react distinctly with Ni(II), Cr(VI), and Hg(II) were then covalently coupled to these functional groups. These functionalized C-mu PADs were then evaluated for heavy metals ions detection with spiked water samples. Using a single-plex platform, we achieved detection limits as low as 0.24 ppm for Ni(II), 0.18 ppm for Cr(VI) and 0.19 ppm for Hg(II). The detection limits for this single-plex platform were twice as good as those obtained in previous studies using colorimetric analysis due to the formation of homogeneous metal complexes from immobilized chromogenic reagents. Furthermore, by minimizing cross-reaction with chelating agents and maximizing reaction uniformity, multiplex heavy metal ion detection was successfully demonstrated for lake-water samples spiked with various concentrations of heavy metal ions with high precision. This functionalized C- PAD provides a highly portable and rapid on-site monitoring platform for multiple heavy metal ions detection with extremely high repeatability, which is useful for resource limited areas and developing countries.