Quantitative assessment of tip effects in single-molecule high-speed atomic force microscopy using DNA origami substrates.

High-speed atomic force microscopy (HS-AFM) is widely employed in the investigation of dynamic biomolecular processes at a single-molecule level. However, it remains an open and somewhat controversial question, how these processes are affected by the rapidly scanned AFM tip. While tip effects are commonly believed to be of minor importance in strongly binding systems, weaker interactions may significantly be disturbed. Here, we quantitatively assess the role of tip effects in a strongly binding system using a DNA origami-based single-molecule assay. Despite its fM dissociation constant, we find that HS-AFM imaging can disrupt monodentate binding of streptavidin (SAv) to biotin (Bt) even under gentle scanning conditions. To a lesser extent, this is also observed for the much stronger bidentate SAv-Bt complex. This demonstrates the importance of a careful and quantitative evaluation of tip effects in the HS-AFM imaging also of strongly binding systems. The presented DNA origami-based assay can be universally employed to quantify tip effects in strongly and weakly binding systems and to optimize the experimental settings for their reliable HS-AFM imaging.