Pb2+ induced DNA conformational switch from hairpin to G-quadruplex: electrochemical detection of Pb2+

Conformational switch from hairpin DNA to G-quadruplex induced by Pb2+ is studied by electrochemical impedance spectroscopy ( EIS) in the presence of [Fe(CN)(6)](3-/4-) as the redox probe. In the presence of Pb2+, the G-rich hairpin DNA opens the stem-loop and forms G-quadruplex structure, which gives rise to a sharp increase in the charge-transfer resistance (R-CT) of the film reflected by the EIS. This structural change is also confirmed by circular dichroism (CD) measurements and UV-Vis spectroscopic analysis and calculated by density functional theory (DFT). On the basis of this, we develop a label-free electrochemical DNA biosensor for Pb2+ detection. With increasing concentrations of Pb2+, the differences in the charge-transfer resistance RCT before and after the Pb2+ incubation is linearly dependent on the logarithm of Pb2+ concentration within a range from 50 mM to 0.5 nM. The biosensor also exhibits good selectivity for Pb2+ over other metal ions. This is a simple and label-free electrochemical method for Pb2+ detection making use of the G-quadruplex.