An efficient fluorescence reversible regulation strategy with single labelled oligonucleotide HEX-OND successively triggered by Hg(II) and Cysteine: The application and mechanism.

An efficient fluorescence reversible regulation system with HEX-OND was developed. Then the application potential was explored in probing Hg(II) & Cysteine (Cys) in real samples and the thermodynamic mechanism was further investigated by precise theory analysis combining multiple spectroscopic methods. The results showed that only mere disturbances were observed among 15 and 11 kinds of other substances for the optimal system in detecting Hg(II) & Cys, respectively; The linear ranges of quantification were identified as 1.0 ∼ 14.0 and 2.0 ∼ 20.0 (×10 mol/L) with LODs of 8.75 and 14.09 (×10 mol/L) for Hg(II) and Cys, respectively; no significant deviations were found in the quantification results of Hg(II) in three traditional Chinese herbs and Cys in two samples between the well-understood methods with ours respectively, showing excellent selectivity, sensitivity, and tremendous application feasibility. The detailed mechanism was further verified as that the introduced Hg(II) forced HEX-OND to transform into the Hairpin structure with the apparent equilibrium association constant of 6.02 ± 0.62 × 10 L/mol in the bimolecular ratio, leading to the equimolar quencher, consecutive two guanine bases ((G)), approaching and spontaneously static-quenching the reporter HEX (hexachlorofluorescein) (equilibrium constant, 8.75 ± 1.97 × 10 L/mol) in the Photo-induced Electron Transfer (PET) way that was driven by the Electrostatic Interaction. The additional Cys destructed the equimolar Hairpin structure with the apparent equilibrium constant of 8.87 ± 2.47 × 10 L/mol through breaking one of the formed T-Hg(II)-T mismatches by association with the involved Hg(II), occasioning (G) apart from HEX and consequently the fluorescence recovery.