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.

Keywords: Catalytic hairpin assembly; Electrochemical biosensor; Pb(2+); Pb(2+)-dependent DNAzyme.