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 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 PP-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.