Abstract
Microfluidic paper analytical devices (μPADs) have low cost and simple analytical characteristics, which are preferable for on-site analysis and easy assay, but simplicity is often related to low sensitivity. In this work, we demonstrate the utilization of insoluble organic nanocrystals immobilized on μPADs for colorimetric detection of metal ions with sample enrichment. By applying a large volume of an aqueous metal ion solution, the resulting insoluble metal complex gave a sufficiently high color for ppb-level analysis. The present method successfully detected 27.1 ppb (0.5 μM) Fe2+ in artificial river water by applying 100 μL of sample and 5.4 ppb (0.1 μM) Fe2+ with a 300 μL sample. The detection limit was 2.4 ppb (0.043 μM) in a river water sample containing a complex mixture of ions. With the loading of organic nanocrystals, the sensitivity of μPAD heavy metal analysis was greatly improved, and its quantification ability will be useful for multiple ion analysis.
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