Amplified Surface Plasmon Resonance and Electrochemical Detection of Pb²⁺ Ions Using the Pb²⁺-Dependent DNAzyme and Hemin/G-Quadruplex as a Label

Abstract

The hemin/G-quadruplex nanostructure and the Pb²⁺-dependent DNAzyme are implemented to develop sensitive surface plasmon resonance (SPR) and electrochemical sensing platforms for Pb²⁺ ions. A complex consisting of the Pb²⁺-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 Pb²⁺ ions, the Pb²⁺-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 Pb²⁺ 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 Pb²⁺ 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 H₂O₂. This method enables the detection of Pb²⁺ with a detection limit of 1 pM. Both sensing platforms reveal selectivity toward the detection of Pb²⁺ ions