An electrochemical biosensor based on a highly loaded 3D DNA nanostructure for ultrasensitive detection of Pb2+

Herein, a novel three-dimensional (3D) DNA nanostructure with highly loaded capacity of methylene blue (MB) as signal molecule was constructed to fabricate an electrochemical biosensor for ultrasensitive detection of Pb2+. First, a small amount of target Pb2+ could be converted into numerous mimic targets D1, S1, D2 and S1 ' with the assistant of Pb2+-dependent DNAzyme cleavage cycling, which could trigger MB labeled hairpin DNA H3, H4, H5 and H6 to undergo hybridization chain reaction (HCR) for forming layer A and layer B, respectively. Then, the proposed 3D DNA nanostructure was constructed by layer-by-layer assembly of the prepared layer A and layer B labeled with abundant MB for endowing the 3D DNA structure with excellent carrying capacity of MB and generating a remarkable electrochemical signal. Impressively, when the number of the assembly layers reached four, the optimal electrochemical signal value was obtained for achieving the ultrasensitive detection of Pb2+ with a low detection limit of 2.61 pM. Consequently, the proposed strategy provided a promising approach to design a novel 3D DNA structure with high loading capacity of signal molecule to construct high-performance sensor platform for ultrasensitive detection of biomarkers in diseases diagnosis and environmental monitoring.