Label-Free and Enzyme-Free Colorimetric Detection of Pb2+ Based on RNA Cleavage and Annealing-Accelerated Hybridization Chain Reaction.

A label-free and enzyme-free colorimetric sensor for rapid detection of Pb2+ is reported, which is based on the strategy of DNAzyme-mediated RNA cleavage combined with an annealing-accelerated DNA hybridization chain reaction (HCR). As a trigger DNA, the substrate strand (STM) of DNAzyme can initiate HCR effectively. However, when it is cleaved by DNAzyme in the presence of Pb2+, the separation of DNA functional domains leads to a serious decrease in HCR efficiency. As a result, the difference in Pb2+ concentration converts into the difference of DNA assembly, which eventually leads to the color change of colloidal gold nanoparticles (AuNPs). In this work, a DNA strand (cGR5) completely complementary to the catalytic strand (GR5) of DNAzyme is used to improve the dissociation of STM to enhance the HCR efficiency. In addition, the simple operation of DNA annealing is first used to accelerate the HCR process, enabling the Pb2+ detection to be completed in about 30 min. As advantages of high sensitivity, good selectivity, strong anti-interference ability, and good practical performance are achieved, it is anticipated that the cheap and simple colorimetric sensor will be helpful for on-site detection of environmental and food samples.