Controlling interfacial electron transfer and electrocatalysis by pH- or ion-switchable DNA monolayer-modified electrodes

Abstract

pH-stimulated formation and dissociation of i-motif DNA nanostructures associated with electrodes lead to the control of interfacial electron transfer resistances in the presence of Fe(CN)₆^3−/4− as a redox label (measured by Faradaic impedance spectroscopy). While at neutral pH (pH = 7.0), the interfacial electron transfer resistance is high, R_et ∼ 500 Ω, in the presence of the i-motif nanostructure (pH = 5.8) it decreases to R_et ∼ 300 Ω. By cycling the pH of the solution between the values 7.0 and 5.8, the electron transfer resistances are reversibly switched between high and low values, respectively. The switchable charge transport at the modified electrode is rationalized in terms of the electrostatic interactions between the modified electrode and the redox label. Similarly, the generation of a G-quadruplex through the formation of an aptamer–AMP complex leads to the control of the interfacial electron transfer resistance. The i-motif- or G-quadruplex-controlled electron transfer resistances are implemented to yield the switchable electrocatalyzed reduction of H₂O₂ in the presence of negatively charged, citrate-stabilized, Ag nanoparticles.