State Key Laboratory of Chem/Biosensing and Chemometrics, Chemistry and Chemical Engineering
College, Hunan University, Changsha, Hunan 410082, China

A highly selective fluorescence sensor was developed for Hg(II) ion detection in aqueous solutions based on the selective binding of Hg(II) ions with a pair of thymine-thymine mismatch. The sensor consists of two DNA probes functionalized with a fluorophore (fluorescein, F) and a quencher (tetramethyl rhodamine, Q) moiety separately. This pair of DNA probes contains two pairs of thymine-thymine mismatches used to detect Hg(II) ions. In the presence of Hg(II) ions, thymine-Hg2＋-thymine was formed between thymine residues of probes. From that, the interaction of the two DNA probes increased. Thus, the DNA probes formed a double-stranded structure. Both the fluorophore and quencher were brought close to each other leading to the fluorescence resonance energy transfer (FRET) between F and Q. Under the optimum conditions, the sensor was used to detect the Hg(II) ions from 50 to 1000 nmol•L－1 with a regression equation y＝5281.13－1650.56 lg[Hg2＋] (R2＝0.985). The linear range covers 100 to 500 nmol•L－1, and the limit of detection (LOD) is 79 nmol•L－1. The disturbance of some co-existing metal ions was explored, and no significant fluorescence quenching in the presence of 1.0 µmol•L－1 other metal ions was observed. The fluorescence sensor has good sensitivity and selectivity for Hg(II) ions providing a rapid, simple and low cost method for the detection of mercury(II) ions in aqueous solutions.