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 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

Block Copolymer Patterns as Templates for the Electrocatalyzed Deposition of Nanostructures on Electrodes and for the Generation of Surfaces of Controlled Wettability

ITO electrodes modified with a nanopatterned film of polystyrene-<i>block</i>-poly­(2-vinylpyridine), PS-<i>b</i>-P2VP, where the P2VP domains are quaternized with iodomethane, are used for selective deposition of redox-active materials. Electrochemical studies (cyclic voltammetry, Faradaic impedance measurements) indicate that the PS domains insulate the conductive surface toward redox labels in solution. In turn, the quaternized P2VP domains electrostatically attract negatively charged redox labels solubilized in the electrolyte solution, resulting in an effective electron transfer between the electrode and the redox label. This phenomenon is implemented for the selective deposition of the electroactive Prussian blue on the nanopatterned surface and for the electrochemical deposition of Au nanoparticles, modified with a monolayer of <i>p</i>-aminothiophenol/2-mercaptoethanesulfonic acid, on the quaternized P2VP domains. The patterned Prussian blue-modified surface enables controlling the wettability properties by the content of the electrochemically deposited Prussian blue. Controlled wettability is unattainable with the homopolymer-modified surface, attesting to the role of the nanopattern