Paper on multifrequency AFM
We wrapped up our investigation of the surface structure of TMV: "Multifrequency Force Microscopy of Helical Protein Assembly on a Virus"
A. Calò, A. Eleta-Lopez, P. Stoliar, D. de Sancho, S. Santos, A. Verdaguer, A.M. Bittner
Sci. Rep. 6 (2016) 21899, DOI: 10.1038/srep21899
We relied on raw AFM data and power spectra from adsorbed virus particles, but compared standard AFM with multifrequency AFM, where the cantilever is excited at two (or more) frequencies. In this way we were able to detect the 6.9 nm repeat, but also the 2.3 nm helical pitch of the coat proteins that make up the Tobacco mosaic virus TMV. This was as yet only achieved with averaging methods (X-ray diffraction, cryo electron microscopy reconstruction), but never on a single virion. The problem is lateral AFM resolution, but also an irregular superstructure on the surface.