Atomic Force Microscopy Measurements of Intermolecular Binding Strength - Methods in Molecular Biology: Extracellular Matrix Protocols - page 106

Fig. 1. Schematic representation of AFM measurements of intermolecular binding
strength between glyconectin 1 proteoglycans in physiological solution. Yellow force
distance curve represent measurements in artificial sea water with physiological
10 m M Ca 2+ and red curve is obtained with 2 m M Ca 2+ . Adhesion molecule abbrevi-
ated as am symbolizes glyconectin 1.
bamate and acylimidazoles, respectively. Amine-containing molecules (pro-
teins, glycoproteins, proteoglycans, and glycans containing linkage amino acid)
will be rapidly and quantitatively coupled to these groups to yield stable car-
bamate and amide linkages, respectively. Unreacted imidazole carbamate will
hydrolyze in the presence of water to the hydroxyl groups and imidazole.
The cantilever tip with attached cell-adhesion molecule is carefully moved
with subnanometer precision with AFM piezoelectric scanner toward the
complementary receptor on the mica surface in the liquid cell containing physi-
ological solution until contact between two molecules is made ( Fig. 1 ). This
approach is followed by retraction of the cantilever tip. During such a dislodg-
ment, the cantilever bends until the pulling force becomes equivalent to the
intermolecular binding strength between adhesion molecules crosslinked to the
tip and receptor attached to the mica. When the power applied by AFM piezo-
electric scanner tube exceeds ligand-receptor binding force, the lever jumps
off the contact and straitens. The cantilever deflection and distance from the
surface is permanently monitored by deflection of the laser from the cantilever