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 Pb2+, 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 spectra 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 R CT difference (ΔR 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 Pb2+, 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.