The development of a paper-based distance sensor for the detection of Pb assisted with the target-responsive DNA hydrogel.

Due to the serious risks of lead pollution to human health, it plays a great role in constructing a simple, inexpensive, portable, and user-friendly strategy for Pb detection in environmental samples. Herein, a paper-based distance sensor is developed to detect Pb assisted with the target-responsive DNA hydrogel. Pb can activate DNAzyme to cleave its substrate strand, which results in the hydrolysis of the DNA hydrogel. The released water molecules trapped in the hydrogel can flow along the patterned pH paper due to the capillary force. The water flow distance (WFD) is significantly influenced by the amount of water released from the collapsed DNA hydrogel triggered by the addition of various Pb concentrations. In this way, Pb can be quantitatively detected without using specialized instruments and labeled molecules, and the limit of detection (LOD) of Pb is 3.0 nM. Additionally, the Pb sensor works well in lake water and tap water. Overall, this simple, inexpensive, portable, and user-friendly method is very promising for quantitative and in-field detection of Pb with excellent sensitivity and selectivity.