A universal converting strategy based on target-induced DNA nanoprobe conformational change for lead (II) ion assay

In this work, an electrochemical biosensor combining a novel enzyme-free converting strategy and branched hybridization chain reaction (bHCR) signal amplification for sensitive detection of Pb²⁺ is constructed. Herein, inspired by Holliday junctions nanostructure, a relatively symmetric and stable four-way junction nanostructure probe was prepared by using four DNA stands hybridization including P, S1, S2 and help DNA (hD) with rational design and immobilized onto Au@Fe₃O₄ for rapid separation. With unique advantage of nanoprobe, target Pb²⁺ will induce the probe conformational change and release S1, S2 from the Au@Fe₃O₄ scaffold to solution, realizing the conversion of input one target Pb²⁺ into two DNA outputs with enzyme-free. To further improve the performance of biosensor, bHCR can be triggered by using S1 and S2 as initiator simultaneously to form reticulated dsDNA nanostructure on the surface of electrode. Then, methylene blue (MB) as electron mediator was embedded into the reticulated dsDNA nanostructure to produce a detection signal. This method introduced a universal converting strategy that molecular unrelated to nucleic acids trigger nucleic acids amplification technology with the help of enzyme-free, which not only widen the application of nucleic acids amplification technology, but also has benefited for molecular analysis.