Metal ion enrichment using organic nanocrystal coatedmicrofluidic paper analytical devices to achieve highly sensitive colorimetric detection

Low sensitivity is a common issue in the colorimetric of microfluidic paper analytical device (μPADs) for heavy metal ion detection. In this work, we demonstrated the utilization of insoluble organic nanocrystal (NCs) coated on μPADs both for reagent and sample enrichment. By applying a large volume of aqueous metal solution, NCs absorbed Fe²⁺ until it reached high capacity, leading to an obvious color change even at ppb-level. NCs coated-μPADs successfully detected 5.4 ppb (0.1 μM) of Fe²⁺ which meets the criteria to detect the ion in a reference river water sample (6.9 ppb), a sensitivity higher than other comparable sensing device.