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We demonstrate a novel approach for rapid, selective, and sensitive detection of heavy metals using a solid-phase bioactive lab-on-paper sensor that is inkjet printed with sol–gel entrapped reagents to allow colorimetric visualization of the enzymatic activity of β-galactosidase (B-GAL). The bioactive paper assay is able to detect a range of heavy metals, either alone or as mixtures, in as little as 10 min, with detection limits as follows: Hg(II) = 0.001 ppm; Ag(I) = 0.002 ppm, Cu(II) = 0.020 ppm; Cd(II) = 0.020 ppm; Pb(II) = 0.140 ppm; Cr(VI) = 0.150 ppm; Ni(II) = 0.230 ppm. The paper-based assay was immune to interferences from nontoxic metal ions such as Na⁺ or K⁺, could be used to detect heavy metals that were spiked into tap water or lake water, and provided quantitative data that was in agreement with values obtained by atomic absorption. With the incorporation of standard chromogenic metal sensing reagents …