A rapid, multiplexed, and naked-eye-readable paper assay for detecting heavy metal pollution in food using a catalytic colorimetric reaction

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Heavy metal contamination is a serious food safety issue.Herein, we report a rapid, multiplexed, and nakedeye-readable method for detecting heavy metal pollution in food samples, including milk, using an inexpensive colorimetric paper.We leverage the urease catalysis reaction to amplify the presence of the heavy metal ions Hg 2+ and Pb 2+ by exploiting their strong inhibitory effect on urease.Integrating with a paper-folding strategy, the visual assay realizes rapid detection of over 10 samples within 5 min.It allowed detection of Hg 2+ as low as 0.1 nM and Pb 2+ as low as 2 μM.Results can be visually interpreted with the naked eye or a smartphone, making it practical for on-site testing and ensuring the safety of dairy products against metal contamination.