Fig. 2

Force-distance curve-based AFM. a Principle of force-distance (FD) curves by approaching (red) and withdrawing (blue) the AFM tip from the sample. The tip of the cantilever is initially distant from the sample [1] to which it is brought into contact [2]. During retraction [3] of the AFM tip, adhesive events may occur at different distances due to nonspecific [4] or specific [5] interactions between tip and sample. b The force-curve plot from an AFM measurement. The slope value is fitted with a linear fit (red line) (a), the adhesion is measured as a single value and the mechanical value of the point (b) indicates the adhesion force