Highly sensitive detection of Pb²⁺ in the environment with DNAzyme and rolling circle amplification reaction

Lead (Pb²⁺) is a toxic heavy metal that can severely pollute the environment and cause harm to public health. Therefore, the prompt and accurate monitoring of lead levels in the environment is vital. In this study, a novel DNAzyme-based cascade signal amplification biosensor that could detect Pb²⁺ with high sensitivity was designed through the combination of the strand displacement reaction (SDR) and rolling circle amplification (RCA). When Pb²⁺ is absent, RCA is triggered under the synergistic action of T4 DNA ligase and phi29 DNA polymerase with an artificially fluorophore-labeled S-chains being released to replace the upstream products generated by repeated RCA, thereby restoring the quenched fluorescence and emitting a strong fluorescent signal. After adding Pb²⁺, 8-17 DNAzyme binds specifically to Pb²⁺ and catalyzes the cleavage of the rA site on a single-stranded DNA with artificially modified rA site to restrict the RCA. The designed sensor provides a linear detection range for Pb²⁺ from 25 pM to 1 µM, with a low limit of detection 8.3 pM. Significantly, this sensor still demonstrates satisfactory performance when used for detecting Pb²⁺ in environment samples (e.g., river water). We consider that our study can provide reference values and ideas for the development of heavy metal ion detection methods.