Reagentless, Electrochemical Aptasensor for Lead (II) Detection

Abstract

A novel strategy for selective and sensitive amperometric detection of lead ion (Pb2+) was proposed based on target-inducedconformational switch. The ferrocene-labeled aptamer thiol was self-assembled through S-Au bonding on a gold electrode surface and thesurface was blocked with 2-mercaptoethanol to form a mixed monolayer. The aptamer-modified electrode was characterized electrochemicallyby differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). The modified electrode showed a voltammetricsignal due to a one-step redox reaction of the surface-confined ferrocenyl moiety of the aptamer immobilized on the electrodesurface in 20mM Tris–HCl buffers buffer of pH 7.4. The “signal-on” upon Pb2+ association could be attributed to a change in conformationfrom random coil-like configuration on the probe-modified film to the quadruplex structure. The fabricated biosensor showed alinear 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 showgood potential for Pb2+ detection in real Chinese herb samples.