Impedimetric Immobilized DNA-Based Sensor for Simultaneous Detection of Pb2+, Ag+, and Hg2+

An unlabeled immobilized DNA-based sensor was reported for simultaneous detection of Fb(2+), Ag+, and Hg2+ by electrochemical impedance spectroscopy (EIS) with [Fe(CN)(6)](4-/3-) as redox probe, which consisted of three interaction sections: Pb2+ interaction with G-rich DNA strands to form G-quadruplex, Ag+ interaction with C-C mismatch to form C-Ag+-C complex, and Hg2+ interaction with T-T mismatch to form T-Hg2+-T complex. Circular dichroism (CD) and UV-vis Tara indicated that the interactions between DNA and Pb2+, Ag+, or Hg2+ occurred. Upon DNA interaction with Pb2+, Ag+, and Hg2+, respectively, a decreased charge transfer resistance (R-CT) was obtained. Taking advantage of the RcT difference (Delta R-CT), Pb2+, Ag+, and Hg2+ were selectively detected with the detection limit of 10 pM, 10 nM, and 0.1 nM, respectively. To simultaneously (or parallel) detect the three metal ions coexisting in a sample, EDTA was applied to mask Pb2+ and Hg2+ for detecting Ag+; cysteine was applied to mask Ag+ and Hg2+ for detecting Fb(2+), and the mixture of G-rich and C-rich DNA strands were applied to mask Pb2+ and Ag+ for detecting Hg2+. Finally, the simple and cost-effective sensor could be successfully applied for simultaneously detecting Pb2+ Ag+, and Hg2+ in calf serum and lake water.