Electrochemical biosensor for sensitive detection of Hg2+ baesd on clustered peonylike copper-based metal-organic frameworks and DNAzyme-driven DNA Walker dual amplification signal strategy

A sensitive electrochemical biosensor was constructed for Hg2+ detection based on peonylike Cu-MOFs in situ growth of PtPd NPs bimetallic label S1 and Mg2+-dependent DNAzyme-driven DNA Walker dual amplification signal strategy. The hairpin DNA (HP) and signal label Cu-MOFs@PtPd NPs/S1 were first used to self-assemble on the gold nanorods/poly (diallyldimethylammonium chloride) functionalized graphene (AuNRs/PDDA-Gr) modified electrode, at this time, Cu ions can undergo a valence change to produce a larger initial signal. Here, we designed S-2 that can perform dual functions and contains two sequences, on was a substrate sequence of the Mg2+-dependent DNAzyme and the other was a sequence complementary to HP. In the presence of target Hg2+, HP was opened and hybridized with enzymatically sequenced DNA Walker (S-2) to preferentially form thymine Hg2+-thymine (T-Hg2+-T). Then, DNA Walker exhibited catalytic activity of DNAzyme in the presence of Mg2+ to continuously cleave Cu-MOFs@PtPd NPs/S1, resulting in a decrease of electrochemical signal. Under optimal conditions, the change of current was linearly related to the negative logarithm of the Hg2+ concentration in the detection range of 0.001-100 nM with a low detection limit of 0.52 pM. Moreover, the proposed aptasensor was successfully applied in detection of milk powder samples.

Automated summary

A sensitive electrochemical biosensor for Hg2+ detection was developed using a dual amplification signal strategy, showing linear detection range from 0.001-100 nM and a low detection limit of 0.52 pM. This biosensor was successfully applied in detecting Hg2+ in milk powder samples.