We have developed a fluorescence technique for the detection of Hg2+and Pb2+ions using polythymine (T33)/ benzothiazolium-4-quinolinium dimer derivative (TOTO-3) and polyguanine (G33)/terbium ions (Tb3+) conjugates, respectively. Hg2+ions induce T33to form folded structures, leading to increased fluorescence of the T33/TOTO-3 conjugates. Because Pb2+ions compete with Tb3+ions to form complexes with G33, the extent of formation of the G33-Tb3+complexes decreases upon increasing the Pb2+concentration, leading to decreased fluorescence at 545 nm when excited at 290 nm. To minimize interference from Hg2+ions during the detection of Pb2+ions, we conducted two-step fluorescence measurements; prior to addition of the G33/Tb3+probe, we recorded the fluorescence of a mixture of the T33/TOTO-3 conjugates and Hg2+ions. The fluorescence signal obtained was linear with respect to the Hg2+concentration over the range 25.0-500 nM (R2= 0.99); for Pb2+ions, it was linear over the range 3.0-50 nM (R2= 0.98). The limits of detection (at a signal-to-noise ratio of 3) for Hg2+and Pb2+ions were 10.0 and 1.0 nM, respectively. Relative to other techniques for the detection of Hg2+and Pb2+ions in soil and water samples, our present approach is simpler, faster, and more cost-effective. © 2011 Elsevier B.V. All rights reserved.
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