On-demand controlled bidirectional DNAzyme path for ultra-sensitive heavy metal ion detection†

A bidirectional self-powered biosensor is constructed for the quasi-simultaneous detection of Pb²⁺ and Hg²⁺ based on MoS₂@CuS heterostructures as an accelerator and hybridization chain reaction (HCR) as a signal amplification strategy. MoS₂@CuS heterostructures significantly facilitate electron transfer between glucose and bioelectrodes, thereby greatly improving the detection signal of self-powered biosensors. This novel biosensor employs the unique sequences of DNAzymes to isolate Pb²⁺ and Hg²⁺ by the cleavage effect and thymine (T)–Hg²⁺–thymine (T) structures, respectively. In the process, Pb²⁺ cuts the sequence of DNAzyme at the bioanode to trigger glucose oxidation to monitor Pb²⁺. The as-formed T–Hg²⁺–T structures activate HCR to reduce [Ru(NH₃)₆]³⁺ to detect Hg²⁺ at the biocathode. It is noteworthy that this biosensor not only realizes Pb²⁺ or Hg²⁺ detection in a single-electrode, respectively, but also can quasi-simultaneously detect both Pb²⁺ and Hg²⁺ in the bioanode and the biocathode. The novel self-powered biosensor identifies Pb²⁺ in the range of 10⁶ fM to 10 fM with a limit of detection (LOD) of 3.1 fM and Hg²⁺ in the range of 10⁶ fM to 1 fM with an LOD of 0.33 fM.