A G-quadruplex based fluorescent oligonucleotide turn-on probe towards iodides detection in real samples

•A turn-on fluorescent OND probe is designed to detect iodides in actual samples.•Hg(II) ions can lead to the fluorescent quenching of the designed ONDs.•I− can extract Hg2+ from T-Hg(II)-T leading to fluorescence recovery of ONDs.

A basket-type G-quadruplex (GQ) fluorescent oligonucleotide (OND) probe is designed to detect iodides dependent on thymine-Hg(II)-thymine (T-Hg(II)-T) base pairs and the intrinsic fluorescence quenching capacity of GQ. In the presence of Hg(II) ions (Hg2+), the two hexachloro-fluorescein-labeled ONDs form a hairpin structure and the fluorophores are dragged close to the GQ, leading to fluorescence quenching of the probe due to photoinduced electron transfer. Upon addition of iodide anions, Hg2+ are extracted from T-Hg(II)-T complexes which attributes to the stronger binding with iodide anions, resulting in the fluorescence recovery. Through performing the fluorescence quenching and recovery processes, this probe developed a fluorescence turn-on sensor for iodide anions determination over a linear range of 20-200 nmol/L with a limit of detection of 5 nmol/L. The practical use of the turn-on technology was demonstrated by its application in determination of iodides in water, food, pharmaceutical products and biological samples.