AFM-FS

In AFM single molecule dynamic force spectroscopy (AFM-FS), binding forces between two molecules of interest are measured by functionally immobilizing them on two different surfaces (i.e. the tip of an AFM and an appropriate counter surface) that are brought in mechanical contact under physiological conditions (see Figure 2). 

In our AFM-FS experiments of protein-DNA complexes, the respective DNA target sequences were covalently coupled to Si3N4 AFM cantilevers via monolayer activation and a functional heterobifunctional spacer molecule. The corresponding (His)6ExpG protein was immobilized on a silanized mica surfaces by a short linker molecule coupled to one of the five ExpG lysines. We used a commercial AFM instrument at 25°C that has been modified with a home-built electronics and data acquisition (Bartels et al. 2003). 

McGuiggan et al. [982] measured the friction on mica surfaces coated with thin films of either perfluoropolyether (PFPE) or polydimethylsiloxane (PDMS) using three different methods the surface forces apparatus (radius of curvature of the contacting bodies 1 cm), friction force microscopy with a sharp AFM tip R 20 nm), and friction force microscopy with a colloidal probe R 15 pm). In the surface force apparatus, coefficient of frictions of the two materials differed by a factor of fs 100, whereas for the AFM silicon nitride tip, the coefficient of friction for both materials was the same. When the colloidal probe technique was used, the coefficient of frictions differed by a factor of 4. This can be explained by the fact that, in friction force microscopy experiments, the contact pressures are much higher. This leads to a complete penetration of the AFM tip through the lubrication layer, rendering the lubricants ineffective. In the case of the colloidal probe, the contact pressure is reduced and the lubrication layer cannot be displaced completely. 

Figure II. 11 Subternary C3A-CaS04-CaCl2 ternary diagram from Nielsen et al. (2003). Ett ettringite Fs Friedel s salt Hs hemisulfate Ks Kuzel s salt Ms monosulfete. See Table I l.l for phase composition. (From Nielsen, E. P. et al.. Effect of solid solutions of AFm phases on chloride binding. Proceedings of the Nth International Congress on the Chemistry of Cement, Durban, South Africa, 2003.)...

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