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

Abstract

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, including milk, using an inexpensive colorimetric paper. We leverage the urease catalysis reaction to amplify the presence of the 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 detection of Hg²⁺ as low as 0.1 nM and Pb²⁺ 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.