Design of metal-ion-triggered assembly of label-free split G-quadruplex/duplex DNA for turn-on detection of Hg2+ in fetal calf serum

Abstract

A simple oligonucleotide-based label-free turn-on fluorescent Hg2+ sensor depending on the transformation of the random single-stranded DNA (ssDNA) into a G-quadruplex/double-stranded DNA (dsDNA) assemble has been developed. The proposed sensor combines the advantages of the huge enhancement of Thioflavin T binding to G-quadruplex/dsDNA assemble and high selectivity of the thymine (T)-T mismatched base pairs to Hg2+. In the presence of Hg2+, the two separated ssDNA prefer to form a metal-dsDNA complex, which results in the two G-rich segments connecting to each other and forming a split G-quadruplex complex. First, the reporter ThT bind to the G-quadruplex and then intercalate to dsDNA, resulting in remarkable fluorescence enhancement (∼16-fold). The sensor affords a high sensitivity for Hg2+, with a low limit of detection (LOD) of 10nM based on a calculation of 3σ/slope. The main features of the proposed sensor include: (1) Simple design and easy operation, (2) the proposed sensor displays high sensitivity and lower limit of detection for Hg2+. (3) Environmental friendly and being used for assessing Hg2+ levels in fetal calf serum (FCS) with satisfactory results.