Sensor Design Based on Structure Adjustment in Loops of G-quadruplex

The effects of linking loop structures between guanine (Gn) repeats on G-quadruplex formation were investigated. The results show that the unfavorable effects of long linking loops on G-quadruplex formation can be overcame by introducing double-stranded structures in linking loop regions. This finding provides a new way for sensor design. That is, the activity of G-quadruplex DNAzyme can be controlled by utilizing target-mediated formation of double-stranded structures in loops. As an example, T-T mismatches are introduced in long loops to destroy their double-stranded structures. The stabilization of Hg2+ to T-T mismatches promotes the reformation of double-stranded structure. Correspondingly, the oligonucleotide folds into G-quadruplex, which binds with Hemin to form peroxidase-like G-quadruplex DNAzyme. Hg2+ sensor is designed and by this method, Hg2+ quantitation is achieved in the concentration range of 10–700 nM, with a detection limit of 8.7 nM. Cysteine (Cys) would compete with T bases to bind with Hg2+, thus releasing Hg2+ from T-Hg2+-T base pairs. As a result, above Hg2+ sensor can also be used in the specific detection of Cys in the range of 20–700 nM with a detection limit of 14 nM.

This work demonstrated that the unfavorable effects of long linking loops on DNA G-quadruplex formation can be overcame by introducing double-stranded structures in linking loop regions, thus providing a new way for sensor design. As examples, G-quadruplex DNAzyme-based sensors were designed for sensitive and selective detection of Hg2+ and cysteine.Figure optionsDownload as PowerPoint slide