'Turn-on' detection of Hg2+ ion using a peroxidase-like split G-quadruplex-hemin DNAzyme

A highly sensitive and selective Hg2+ detection method was developed based on the Hg2+-mediated formation of split G-quadruplex-hemin DNAzymes. In this method, two label-free oligonucleotides are used. In the presence of Hg2+, the two oligonucleotides hybridize to each other to form a duplex, in which T-T mismatches are stabilized by T-Hg2+-T base pair. As a result, the G-rich sequences of the two oligonucleotides can associate to form a split G-quadruplex, which is able to bind hemin to form the catalytically active G-quadruplex-hemin DNAzymes. This can be reflected by an absorbance increase when monitored in the H2O2-ABTS (2,2'-azinobis(3-ethylbenzothiazoline)-6-sulfonic acid) reaction system by using UV-vis absorption spectroscopy. This 'turn-on' process allows the detection of aqueous Hg2+ at concentrations as low as 19 nM using a simple colorimetric technique. With the development of the studies on metal-base pairs, this Hg2+-sensing method can be easily extended to the analysis of other metal ions.