Fluorescence detection of mercury(II) and lead(II) ions using aptamer/reporter conjugates.

We have developed a fluorescence technique for the detection of Hg(2+) and Pb(2+) ions using polythymine (T(33))/benzothiazolium-4-quinolinium dimer derivative (TOTO-3) and polyguanine (G(33))/terbium ions (Tb(3+)) conjugates, respectively. Hg(2+) ions induce T(33) to form folded structures, leading to increased fluorescence of the T(33)/TOTO-3 conjugates. Because Pb(2+) ions compete with Tb(3+) ions to form complexes with G(33), the extent of formation of the G(33)-Tb(3+) complexes decreases upon increasing the Pb(2+) concentration, leading to decreased fluorescence at 545 nm when excited at 290 nm. To minimize interference from Hg(2+) ions during the detection of Pb(2+) ions, we conducted two-step fluorescence measurements; prior to addition of the G(33)/Tb(3+) probe, we recorded the fluorescence of a mixture of the T(33)/TOTO-3 conjugates and Hg(2+) ions. The fluorescence signal obtained was linear with respect to the Hg(2+) concentration over the range 25.0-500 nM (R(2)=0.99); for Pb(2+) ions, it was linear over the range 3.0-50 nM (R(2)=0.98). The limits of detection (at a signal-to-noise ratio of 3) for Hg(2+) and Pb(2+) ions were 10.0 and 1.0 nM, respectively. Relative to other techniques for the detection of Hg(2+) and Pb(2+) ions in soil and water samples, our present approach is simpler, faster, and more cost-effective.