Imaging adhesion forces on proteins with the atomic force microscope

We investigated the adhesion forces between single protein molecules and the silicon-nitride tip of an atomic force microscope. Force curves were taken on a sample with single adsorbed proteins while the tip was raster scanned laterally. Out of these force maps we can calculate several images showing for instance the topography or the adhesion force as a function of lateral position. Two systems were investigated here: actin adsorbed on mica and tubulin adsorbed on positively charged silanized surfaces, the adhesion force of the tip on the protein was smaller by about a factor of three to five compared to the force measured on the substrate. This is in agreement with previous studies of lysozyme and DNA adsorbed on mica. The data were analyzed by estimating the van der Waals force between the tip and a single protein and between the tip and a flat substrate. The measured adhesion force between the tip and the substrate can be understood by van der Waals. However in the case of the proteins the observed adhesion is larger than expected by only van der Waals forces. So we conclude that there are additional interactions determining the adhesion between the tip and the protein.

Duke Scholars

Author Christoph F. Schmidt Physics