Amplified surface plasmon resonance and electrochemical detection of Pb2+ ions using the Pb2+-dependent DNAzyme and hemin/G-quadruplex as a label.

The hemin/G-quadruplex nanostructure and the Pb(2+)-dependent DNAzyme are implemented to develop sensitive surface plasmon resonance (SPR) and electrochemical sensing platforms for Pb(2+) ions. A complex consisting of the Pb(2+)-dependent DNAzyme sequence and a ribonuclease-containing nucleic acid sequence (corresponding to the substrate of the DNAzyme) linked to a G-rich domain, which is "caged" in the complex structure, is assembled on Au-coated glass surfaces or Au electrodes. In the presence of Pb(2+) ions, the Pb(2+)-dependent DNAzyme cleaves the substrate, leading to the separation of the complex and to the self-assembly of the hemin/G-quadruplex on the Au support. In one sensing platform, the Pb(2+) ions are analyzed by following the dielectric changes at the surface as a result of the formation of the hemin/G-quadruplex label using SPR. This sensing platform is further amplified by the immobilization of the sensing complex on Au NPs (13 nm) and using the electronic coupling between the NPs and the surface plasmon wave as an amplification mechanism. This method enables the sensing of Pb(2+) ions with a detection limit that corresponds to 5 fM. The second sensing platform implements the resulting hemin/G-quadruplex as an electrocatalytic label that catalyzes the electrochemical reduction of H(2)O(2). This method enables the detection of Pb(2+) with a detection limit of 1 pM. Both sensing platforms reveal selectivity toward the detection of Pb(2+) ions.