Heavy metal contamination is a serious food safety issue. Herein, we report a rapid, multiplexed and naked-eye readable method for detecting heavy metal pollution in food samples using a cheap colorimetric paper, including milk. We leverage the urease catalysis reaction to amplify the presence of heavy metal ions, Hg2+ and Pb2+, 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 to detection of Hg2+ as low as 0.1 nM and Pb2+ as low as 2 μM, and the results can be read out either by naked eyes or smartphones. 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.
Keywords: Colorimetric detection; Food safety; Heavy metal pollution; Origami paper; Urease.
© 2025, The Authors. Published by Elsevier Inc. on behalf of the American Dairy Science Association®. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).