Activationless Electron Transfer of Redox-DNA in Electrochemical Nanogaps.

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.

Ballistic Brownian Motion of Nanoconfined DNA.

Theoretical treatments of polymer dynamics in liquid generally start with the basic assumption that motion at the smallest scale is heavily overdamped; therefore, inertia can be neglected. We report on the Brownian motion of tethered DNA under nanoconfinement, which was analyzed by molecular dynamics simulation and nanoelectrochemistry-based single-electron shuttle experiments. Our results show a transition into the ballistic Brownian motion regime for short DNA in sub-5 nm gaps, with quality coefficients as high as 2 for double-stranded DNA, an effect mainly attributed to a drastic increase in stiffness.

Electrochemical Shot Noise of a Redox Monolayer.

Redox monolayers are the base for a wide variety of devices including high-frequency molecular diodes or biomolecular sensors. We introduce a formalism to describe the electrochemical shot noise of such a monolayer, confirmed experimentally at room temperature in liquid. The proposed method, carried out at equilibrium, avoids parasitic capacitance, increases the sensitivity, and allows us to obtain quantitative information such as the electronic coupling (or standard electron transfer rates), its dispersion, and the number of molecules.

Nanoscale electrochemical charge transfer kinetics investigated by electrochemical scanning microwave microscopy.

We show how microwave microscopy can be used to probe local charge transfer reactions with unprecedented sensitivity, visualizing surface reactions with only a few hundred molecules involved. While microwaves are too fast under classical conditions to interact and sense electrochemical processes, this is different at the nanoscale, where our heterodyne microwave sensing method allows for highly sensitive local cyclic voltammetry (LCV) and local electrochemical impedance spectroscopy (LEIS). LCV and LEIS allow for precise measurement of the localized charge transfer kinetics, as illustrated in this study for a ferrocene self-assembled monolayer immersed in an electrolyte.

Attoampere Nanoelectrochemistry.

Electrochemical microscopy techniques have extended the understanding of surface chemistry to the micrometer and even sub-micrometer level. However, fundamental questions related to charge transport at the solid-electrolyte interface, such as catalytic reactions or operation of individual ion channels, require improved spatial resolutions down to the nanoscale. A prerequisite for single-molecule electrochemical sensitivity is the reliable detection of a few electrons per second, that is, currents in the atto-Ampere (10 A) range, 1000 times below today's electrochemical microscopes.