Dual dye-labeled G-quadruplex aptasensor for detection of thallium(I) using ratiometric fluorescence resonance energy transfer

A fluorescent probe was developed for ratiometric detection of thallium ions in mineral water samples by modifying a G-rich aptamer (PS2.M − 7) with a fluorescence donor (Cyanine-3, Cy 3 ) and a quencher (Cyanine-5, Cy 5 ). The probe had a random coil structure that changed into a G-quadruplex structure upon binding with Tl + . This change in structure decreased the distance between the donor and acceptor moieties, which resulted in fluorescence resonance energy transfer between Cy 3 and Cy 5 . Under optimized conditions, the limit of detection and linear concentration range for Tl + were 30.1 μM (3σ) and 10 μM–10 mM ( R 2  = 0.9981), respectively. This simple and cost-effective fluorescence sensor provided satisfactory results for detection of thallium ions in spiked mineral water samples.