Filming Biomolecular Processes by High-Speed Atomic Force Microscopy

A review of the application studies of high-speed atomic force microscopy (HS-AFM), in which dynamics of proteins and live cells are visualized, is presented. In HS-AFM set-up, the cantilever tip is always in contact with the sample while scanned across the sample surface during topography acquisition. The cantilever is deflected by the tip-sample interaction. The extent of cantilever deflection, and hence the tip-sample interaction force, is kept constant during scanning by feedback control. In noncontact mode, the so-called frequency-modulation (FM) mode is typically used. The choice of substrate surfaces on which samples are placed is a key to successful dynamic imaging by HS-AFM. The surface of freshly cleaved natural muscovite or synthetic fluorophlogopite mica has frequently been used for AFM imaging because it provides atomically flat surfaces over large areas. If an ATP analog visualizable even with AFM is available, HS-AFM should also be able to visualize the expected cooperative binding and hydrolysis of the ATP analog and concomitant structural changes at the subunit level.