AFM study of F-actin on chemically modified surfaces

Biomolecules, such as DNA and cytoskeleton proteins, self-assemble in long-range-ordered nano-aggregates. The process of formation of these long-range ordered nanostructures have large biological interest but, increasingly, they also offer good inspiration for bottom-up 'fabrication' processes leading to large nanostructured areas with the design embedded in their smaller components, as opposed to the classical top-down nanofabrication. To this end, we report here an atomic force microscopy (AFM) study of the high order self assembly of F-actin on mica. AFM is a classical tool for elucidating the topography of biomolecules-covered surfaces, including proteins, and mica is commonly used as a substrate for AFM imaging at molecular resolution due to its atomically-flat surface. Beyond this classical aspects, the most interesting aspect of our work was the capability of fabrication ordered patterns formed by F-actin filaments, through the tuned interplay between F-actin self-assembly forces and forces applied by the AFM tip in a contact mode. More specifically, increasing the force applied by the AFM tip we could observe the shift from the visualisation of individual actin filaments to parallel actin filaments 'rafts'. Thus we could produce ordered hybrid nano-structured surfaces through a mix-and-match nanofabrication technology.