Amplified Fluorescent Detection of Mercuric Ions by Conjugation of the ThT-induced G-Quadruplex Based Hybridization Chain Reaction

Abstract

A sensitive fluorescent method for the detection of Hg²⁺ was developed based on triple-helix molecular switch (THMS)-induced hybridization chain reaction (HCR) amplification. THMS was composed of a T-rich mercury-specific probe and an initiator probe, designed by the Watson–Crick and Hoogsteen base pairings and employed as a signal trigger. Two hairpin probes containing the G-quadruplex sequence were used as signal amplification elements. In the presence of Hg²⁺, the T-Hg²⁺-T mismatch resulted in disassembling the THMS and releasing the initiator probe. One of the hairpins was opened by the released initiator probe, which triggered a successive cross-opening of two hairpins based the strand displacement principle, resulting in the formation of long-chain DNA with multiple G-quadruplex. When thioflavin T (ThT), a fluorophore, was bound to the G-quadruplex, an obvious fluorescence enhancement would occur. This sensing system enabled the highly sensitive and selective detection of aqueous Hg²⁺ with a limit-of-detection of 10.2 pM.