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.

Function of Graphene Oxide as the "Nanoquencher" for Hg Detection Using an Exonuclease I-Assisted Biosensor.

Graphene oxide is well known for its excellent fluorescence quenching ability. In this study, positively charged graphene oxide (pGO25000) was developed as a fluorescence quencher that is water-soluble and synthesized by grafting polyetherimide onto graphene oxide nanosheets by a carbodiimide reaction. Compared to graphene oxide, the fluorescence quenching ability of pGO25000 is significantly improved by the increase in the affinity between pGO25000 and the DNA strand, which is introduced by the additional electrostatic interaction.