The AFM tip is extended toward and then retracted from the surface as the deflection of the cantilever is monitored as a function of distance. The retraction part of the curve (in red) will show any adhesion force between the tip and the sample. In molecular recognition force measurements, ligand molecules (A) are attached to the AFM tip, whereas receptor molecules (B) are present on the sample surface. Use of a linker molecule (e.g. PEG) results in a characteristic curved unbinding peak as the linker stretches, enabling easier identification of specific unbinding interactions between A and B (see representative curve in inset).