Supplementary Figure 1: Principle of force-distance (FD) curve–based AFM.
From: Imaging G protein–coupled receptors while quantifying their ligand-binding free-energy landscape
(a) FD-based AFM contours the sample surface while oscillating the AFM tip with a sine wave at a frequency of 0.25 kHz. Pixel-by-pixel the AFM tip is approached (blue curve) and retracted (red curve) from the sample. The AFM cantilever deflection measures the force interacting between AFM tip and sample. During these approach and retraction cycles the force vs time (b) and force vs distance (c) is recorded. Thereby, the maximal force (imaging force) used to touch the sample Fi is kept constant using a feedback loop. (c) The mechanical deformation or distance of deformation DDef of a soft biological sample is described by the indentation of a much stiffer AFM tip. This indentation is detected at a certain repulsive force. (d) During retraction, adhesive force FAdh is recorded between the tip and the sample. Using a functionalized cantilever FAdh can detect the rupture of specific interactions between for example a functionalized tip and sample. (e) The parameters extracted from individual force curves can be displayed as maps such as the sample topography (height image) contoured at a given imaging force, the adhesion force or sample deformation1.
1. Medalsy, I., Hensen, U. & Muller, D.J. Imaging and quantifying chemical and physical properties of native proteins at molecular resolution by force-volume AFM. Angew Chem Int Ed Engl 50, 12103-12108 (2011).
