Label-free hairpin probe for the rapid detection of Hg(II) based on T-Hg(II)-T.

A simple thymine-rich mercury-specific oligonucleotide (G9T24C9) was designed to quickly detect Hg(Ⅱ) via thymine-Hg(II)-thymine (T-Hg(Ⅱ)-T) coordination chemistry by using 4',6-diamidinyl-2-phenylindole (DAPI). When the stable GC-paired stem of the DNA hairpin occurred, DPAI could intercalate into the T-Hg(Ⅱ)-T base pairs as a fluorescent recognizer. As a result, the hairpin structure was able to promote the rapid formation of T-Hg(Ⅱ)-T mismatches in the presence of Hg(Ⅱ), trigger DAPI to recognize T-Hg(Ⅱ)-T as well as TA/AT base pairs and restore fluorescence; moreover, fluorescence increases were not observed when Hg(Ⅱ) was not introduced. This method represents a simple strategy to detect Hg(Ⅱ). Taking advantage of the hairpin structure, the fluorescence intensity of the G9T24C9 hairpin probe was positively correlated with the concentration of Hg(Ⅱ) from 2.87 to 1400 nM (R2 = 0.9968), and the limit of detection (3σ) was as low as 2.87 nM. Furthermore, this probe had high selectivity for Hg(Ⅱ) detection. The probe was applied to real samples of pond water for the detection of Hg(Ⅱ), and a recovery rate from 95.9% to 104.4% was obtained.