Accessing the dynamics of end-grafted flexible polymer chains by atomic force-electrochemical microscopy. Theoretical modeling of the approach curves by the elastic bounded diffusion model and Monte Carlo simulations. Evidence for compression-induced lateral chain escape.

The dynamics of a molecular layer of linear poly(ethylene glycol) (PEG) chains of molecular weight 3400, bearing at one end a ferrocene (Fc) label and thiol end-grafted at a low surface coverage onto a gold substrate, is probed using combined atomic force-electrochemical microscopy (AFM-SECM), at the scale of approximately 100 molecules. Force and current approach curves are simultaneously recorded as a force-sensing microelectrode (tip) is inserted within the approximately 10 nm thick, redox labeled, PEG chain layer. Whereas the force approach curve gives access to the structure of the compressed PEG layer, the tip-current, resulting from tip-to-substrate redox cycling of the Fc head of the chain, is controlled by chain dynamics.

Probing the structure and dynamics of end-grafted flexible polymer chain layers by combined atomic force-electrochemical microscopy. Cyclic voltammetry within nanometer-thick macromolecular poly(ethylene glycol) layers.

The combined atomic force-electrochemical microscopy (AFM-SECM) technique was used in aqueous solution to determine both the static and dynamical properties of nanometer-thick monolayers of poly(ethylene glycol) (PEG) chains end-grafted to a gold substrate surface. Approach of a microelectrode tip from a redox end-labeled PEG layer triggered a tip-to-substrate cycling motion of the chains' free ends as a result of the redox heads' oxidation at the tip and re-reduction at the substrate surface. As few as approximately 200 chains at a time could be addressed in such a way.

Fabrication of submicrometer-sized gold electrodes of controlled geometry for scanning electrochemical-atomic force microscopy.

A method for fabricating submicrometer-sized gold electrodes of conical or spherical geometry is described. By generating an electric arc between an etched gold microwire and a tungsten counter electrode, the very end of the gold microwire can be melted and given an overall spherical or conical shape a few hundred nanometers in size. The whole wire is subsequently insulated via the cathodic deposition of electrophoretic paint.