| Summary: | In this work, a paper device consisted of a patterned paper chip, wicking pads, and a base was fabricated. On the paper chip, DNA–gold nanoparticles (DNA–AuNPs) were deposited and Hg<sup>2+</sup> ions could be adsorbed by the DNA–AuNPs. The formed DNA–AuNP/Hg<sup>2+</sup> nanozyme could catalyze the tetramethylbenzidine (TMB)–H<sub>2</sub>O<sub>2</sub> chromogenic reaction. Due to the wicking pads, a larger volume of Hg<sup>2+</sup> sample could be applied to the paper device for Hg<sup>2+</sup> detection and therefore the color response could be enhanced. The paper device achieved a cut-off value of 50 nM by the naked eye for Hg<sup>2+</sup> under optimized conditions. Moreover, quantitative measurements could be implemented by using a desktop scanner and extracting grayscale values. A linear range of 50–2000 nM Hg<sup>2+</sup> was obtained with a detection limit of 10 nM. In addition, the paper device could be applied in the detection of environmental water samples with high recoveries ranging from 85.7% to 105.6%. The paper-device-based colorimetric detection was low-cost, simple, and demonstrated high potential in real-sample applications.
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