To solve the problem of lack of selectivity, thymine–thymine(T–T) mispairs could selectively capture Hg2+in aqueous solutionto form T–Hg2+–T base pairs in DNA duplexes that was reportedin 2006 by the Miyake and Tanaka group [17,18]. The Hg2+ion-mediated T–Hg2+–T pair was more stable than the Watson–Crick(WC) A–T pair [17]. More importantly, this T–Hg2+–T interaction ishighly specific, and the T–T base pair can only be stabilized by Hg2+[18]. By utilizing the strong T–Hg2+–T interaction, many interestingcolorimetric [19–21], electrochemical [22,23], and fluorescent sen-sors [24–27] with excellent performance on selectivity against theinterferences of other metal ions have been developed. However,most of these sensors are limited in their practical use due to poordetection capability in the lower nanomolar range. Thus, the devel-opment of highly sensitive, selective, and ready-to-use methods foraqueous Hg2+remains a challenge [28].