A selective amperometric sensing platform for lead based on target-induced strand release

A novel strategy for selective and sensitive amperometric detection of lead ion (Pb2+) was proposed based on target-induced strand release. The underlying gold electrode was pre-modified with dendritic gold nanoparticles by direct electrodeposition to afford increased electrode surface area for immobilization of thiol group-containing capture DNA molecules. The hybridization of the capture DNA molecules with Pb2+-specific aptamer molecules to form a DNA duplex, into which methylene blue was intercalated, induced measurable electrochemical signal. Upon addition of Pb2+, it could specifically bind to its aptamer to form Pb2+-stablized G-quadruplex and induce the aptamer strand to release from the electrode surface into solution, accompanied by the release of intercalated MB responsible for significant signal reduction. The fabricated biosensor showed a linear response to the logarithm of Pb2+ concentration over the range of 1.0 x 10(-10) M to 1.0 x 10(-7) M with a detection limit of 7.5 x 10(-11) 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 environmental samples.