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

Abstract 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.