Near-infrared Fluorescent Probe Based on Cyanine Scaffold for Sensitive Detection of Uranyl Ions in Living Cells and Water Samples

A novel near-infrared fluorescent probe (probe IR-DTB) for uranyl ion detection has been developed through a substitution reaction on an active chloro group attached to cyanine dye IR-780 with 4-(4,5-Dihydro-2-thiazolyl)-1,3-benzenediol under basic conditions. The probe shows a strong fluorescence with a fluorescence quantum yield of 17.2 % at 795 nm in the absence of uranyl ions in pH 7.4 buffer. The binding of the uranyl ion with the probe causes a blue shift from 775 nm to 765 nm. Theoretical calculations confirmed the nature of the electronic transition in the probe and suggested that two molecules of the probes bind to the uranyl core caused by a flattened structure that perhaps facilitated stacking resulting in aggregation and fluorescence quenching. The probe displays sensitive fluorescence responses to uranyl ions with a fluorescence quenching constant of 198 and a detection limit of 93 nM. The probe was utilized to detect concentration changes of uranyl ions in mitochondria in living cells.