posted on 2024-02-26, 16:36authored byZhiyong Zheng, Simon Grall, Soo Hyeon Kim, Arnaud Chovin, Nicolas Clement, Christophe Demaille
Our recent discovery of decreased reorganization energy
in electrode-tethered
redox-DNA systems prompts inquiries into the origin of this phenomenon
and suggests its potential use to lower the activation energy of electrochemical
reactions. Here, we show that the confinement of the DNA chain in
a nanogap amplifies this effect to an extent to which it nearly abolishes
the intrinsic activation energy of electron transfer. Employing electrochemical
atomic force microscopy (AFM-SECM), we create sub-10 nm nanogaps between
a planar electrode surface bearing end-anchored ferrocenylated DNA
chains and an incoming microelectrode tip. The redox cycling of the
DNA’s ferrocenyl (Fc) moiety between the surface and the tip
generates a measurable current at the scale of ∼10 molecules.
Our experimental findings are rigorously interpreted through theoretical
modeling and original molecular dynamics simulations (Q-Biol code).
Several intriguing findings emerge from our investigation: (i) The
electron transport resulting from DNA dynamics is many times faster
than predicted by simple diffusion considerations. (ii) The current
in the nanogap is solely governed by the electron transfer rate at
the electrodes. (iii) This rate rapidly saturates as overpotentials
applied to the nanogap electrodes increase, implying near-complete
suppression of the reorganization energy for the oxidation/reduction
of the Fc heads within confined DNA. Furthermore, evidence is presented
that this may constitute a general, previously unforeseen, behavior
of redox polymer chains in electrochemical nanogaps.