Emission detection of mercuric ions in aqueous media based-on dehybridization of DNA duplexes

To quantify the presence of mercuric ions in aqueous solution, double-stranded DNA (dsDNA) of poly(dT) was employed using a light switch compound, Ru(phen)₂(dppz)²⁺ (1) which is reported to intercalate into dsDNA of a right-handed B-form. Addition of mercuric ions induced the dehybridization of poly(dT)•poly(dA) duplexes to form a hairpin structure of poly(dT) at room temperature and the metal-to-ligand charge transfer emission derived from the intercalation of 1 was reduced due to the dehybridization of dsDNA. As the concentration of Hg²⁺ was increased, the emission of 1 progressively decreased. This label-free emission method had a detection limit of 0.2 nM. Other metal ions, such as K⁺, Ag ⁺, Ca²⁺, Mg²⁺, Zn²⁺, Mn ²⁺, Co²⁺, Ni²⁺, Cu²⁺, Cd ²⁺, Cr³⁺, Fe³⁺, had no significant effect on reducing emission. This emission method can differentiate matched and mismatched poly(dT) sequences based on the emission intensity of dsDNA.