Mercury ion (Hg²⁺) 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 Hg²⁺ in tea is therefore critical for food safety and public health. Here, we developed an electrochemical biosensor for ultrasensitive Hg²⁺ assay by integrating thymine-Hg²⁺-thymine (T-Hg²⁺-T) mismatch recognition with exonuclease III (EXO III)-assisted dual signal amplification. The sensing mechanism relies on Hg²⁺-triggered formation of T-Hg²⁺-T structures, which activate EXO III to release Hg²⁺ 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 (e.g., Cd²⁺ and Cu²⁺) and reliable performance in real tea samples (93.7%∼103.4% recovery), offering a promising tool for monitoring Hg²⁺ contamination in food products.

汞离子（Hg²⁺）污染对茶叶的安全构成重大风险，因为汞具有高度毒性、生物累积性，并且可能导致神经和肾脏损伤。因此，对茶中Hg²⁺的灵敏监测对于食品安全和公众健康至关重要。在这里，我们开发了一种基于胸腺嘧啶-汞离子-胸腺嘧啶（T-Hg²⁺-T）错配识别与外切酶III (EXO III) 协助双重信号放大的电化学生物传感器，实现了对Hg²⁺的超灵敏检测。该传感机制依赖于Hg²⁺触发形成的T-Hg²⁺-T结构，这些结构激活了EXO III，释放出Hg²⁺进行循环再利用，同时产生报告DNA（RDNA）。通过MOF(Zr)/Th/AuPt纳米复合材料进一步增强了信号放大效果，在此过程中基于锆的金属有机框架（MOF(Zr)）和AuPt纳米颗粒协同催化硫黄素（Th）氧化，产生了强烈的电化学响应。这种双重放大的策略实现了4.45 pM的检测限，超过了传统方法的性能。该生物传感器对干扰金属离子（例如Cd²⁺ 和Cu²⁺）表现出高特异性，并且在实际茶样中表现出可靠的表现力（回收率93.7%∼103.4%），为监测食品中的Hg²⁺污染提供了一种有前景的工具。