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A novel strategy for selective and sensitive amperometric detection of lead ion (Pb2+) was proposed based on target-induced conformational switch. The ferrocene-labeled aptamer thiol was self-assembled through S-Au bonding on a gold electrode surface and the surface was blocked with 2-mercaptoethanol to form a mixed monolayer. The aptamer-modified electrode was characterized electrochemically by differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). The modified electrode showed a voltammetric signal due to a one-step redox reaction of the surface-confined ferrocenyl moiety of the aptamer immobilized on the electrode surface in 20mM Tris–HCl buffers buffer of pH 7.4. The “signal-on” upon Pb2+association could be attributed to a change in conformation from random coil-like configuration on the probe-modified film to the quadruplex structure. The fabricated biosensor showed a linear response to the logarithm of Pb2+ concentration over the range of 5.0×10-10 M to 1.0×10-7 M with a detection limit of 1.2×10-10 M. In addition, this strategy afforded an exquisite selectivity for Pb2+ against other metal ions. The excellent sensitivity and selectivity show good potential for Pb2+ detection in real Chinese herb samples.
aptasensor, lead (II), electrochemical, reagentless
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