Catalytic hairpin assembly assisted target-dependent DNAzyme nanosystem coupled with AgPt@Thi for the detection of lead ion

Abstract

An ultrasensitive electrochemical biosensor for detection of lead ions (Pb2+) is proposed based on catalytic hairpin assembly and target-induced DNAzyme signal amplification strategy. Polyethyleneimine-reduced graphene oxide (PEI-rGO) combined with gold@silver nanosheets (Au@Ag NSs) are used as electrode substrate modification materials, which not only increase the specific surface area but also exhibit stronger conductivity than pure PEI-rGO or Au@Ag NSs. Hairpin chain 1 (HP1) is immobilized on the surface of modified electrode by Au–S. Then trigger (Tr) DNA can induce the opening of the HP1 hairpin, thus exposing the binding sequence to hybridize with Hairpin chain 2 (HP2) and catalyzing the opening and binding of the hairpin HP2. The process is cyclic and will produce abundant HP1-HP2 duplex strands. When Pb2+ is present, it can catalyze DNAzyme (Pb2+-HP2) to specifically cut the substrate chain HP1, and only a partial sequence of HP1 remains on the surface of the electrode. Finally, the signal probe (AgPt@Thi-CP) can be hybridized with the part of the HP1 sequence after being cut to generate a significant electrical signal. Under optimal conditions, the Pb2+ concentration measured by prepared electrochemical biosensor has a good linear relationship in the range of 0.05 pM–5 nM, and the detection limit is 0.028 pM. This method can be used for the trace detection of Pb2+ in tap water samples, and it also provides a platform for the detection of other targets.