"On-Off" electrochemical sensing toward mercury pollution in tea exonuclease III triggered target recycling amplification.

Mercury ion (Hg) pollution in tea poses significant risks to human health due to its high toxicity, bioaccumulation, and potential to cause neurological and kidney damage. Sensitive monitoring of Hg in tea is therefore critical for food safety and public health. Here, we developed an electrochemical biosensor for ultrasensitive Hg assay by integrating thymine-Hg-thymine (T-Hg-T) mismatch recognition with exonuclease III (EXO III)-assisted dual signal amplification. The sensing mechanism relies on Hg-triggered formation of T-Hg-T structures, which activate EXO III to release Hg for cyclic reuse while generating reporter DNA (RDNA). Signal amplification is further enhanced by MOF(Zr)/Th/AuPt nanocomposites, where the Zr-based metal-organic framework (MOF(Zr)) and AuPt nanoparticles synergistically catalyze thionine (Th) oxidation, producing a strong electrochemical response. This dual-amplification strategy achieves a detection limit of 4.45 pM, surpassing that of conventional methods. The biosensor demonstrates high specificity against interfering metal ions (, Cd and Cu) and reliable performance in real tea samples (93.7%∼103.4% recovery), offering a promising tool for monitoring Hg contamination in food products.