Label-free fluorescence "turn-on" strategy for mercury (II) detection based on the T-Hg 2+ -T configuration and the DNA-sensitized luminescence of terbium (III)

A novel label-free fluorescence "turn-on" strategy was developed for the sensitive detection of Hg based on the thymine-Hg -thymine (T-Hg -T) coordination and the fact that single-stranded DNA (ssDNA) greatly enhances the fluorescence of terbium (III) (Tb ), but double-stranded DNA (dsDNA) does not. In the absence of Hg , the mercury-specific DNA (MSD) hybridized with the corresponding complementary strand (cDNA) to form a double helix structure in solution based on Watson-Crick base pairings, which cannot enhance the fluorescence of Tb . In the presence of Hg , MSD preferentially bound with Hg to form the T-Hg -T complex due to the strong affinity of Hg(II) for the T bases of DNA, thus avoiding the hybridization of the cDNA to MSD. The free cDNA can greatly enhance the emission of Tb , leading to a sharp increase in fluorescence intensity. Under the optimized conditions, the increased fluorescence intensity was proportional to the concentration of Hg in the range from 10 to 600 nM, and this method can detect concentrations of Hg as low as 0.24 nM. Moreover, satisfactory results were obtained for the detection of Hg in river water and fish samples, and the results were consistent with those from the atomic fluorescence spectroscopy (AFS). Thus, the fluorescence characteristics of Tb were here used in a "turn on" approach to detect Hg , which represents a new opportunity for Hg analysis in the field of environmental monitoring and food safety.