Professor Kislon Voitchovsky,  Soft and Bio NanoInterfaces Lab,
Durham University, UK

Towards probing the dynamics of single molecules and ions at solid-liquid interfaces
Scanning probe microscopies have enabled unprecedented insights into the assembly, and properties of molecules and ions at interfaces. However, most studies are conducted at equilibrium with little information about the interfacial dynamics. Probing the diffusion of single ions or molecules or ions does not only requires sub-nanometer spatial resolution, but also the ability to probe phenomena on the micro to nano-second timescale.

Here I present recent experimental developments aimed at tackling this problem with high-resolution Atomic Force Microscopy (AFM). For larger molecules naturally diffusing along a solid-liquid interface, AFM can be augmented with ultrafast actuators (>50kHz) to mechanically probe the local diffusion process faster than the moving molecules, for example with fluid lipid membranes. The problem is more challenging for smaller and faster ions. One possible strategy is to use AFM to impose an AC electric field over a range of relevant frequencies and measure its effect on the interface, in an approach analogous to dielectric spectroscopy. While already established, this approach requires significant improvements to achieve highly localised measurements.