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 Hg2+ ions could be adsorbed by the DNA-AuNPs. The formed DNA-AuNP/Hg2+ nanozyme could catalyze the tetramethylbenzidine (TMB)-H2O2 chromogenic reaction. Due to the wicking pads, a larger volume of Hg2+ sample could be applied to the paper device for Hg2+ 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 Hg2+ 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 Hg2+ 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.
Keywords: colorimetric detection; mercury ion; paper device; signal enhancement.