Abstract
The atomic force microscope (AFM) has emerged as a powerful tool for measuring the dynamic strength of intermolecular bonds. The unbinding properties of various ligand–receptor systems including avidin/biotin, antibody/antigen, and p-selectinlcarbohydrate pairs have been characterized by force spectroscopy. These experiments are used to resolve interactions down to a single ligand–receptor pair under well-defined conditions. AFM has also been applied to molecules under more native environments. The chapter presents the binding strength of ligand–receptor interactions has been measured between AFM tips functionalized with specific ligand and receptors on the surface of living cells. In addition to revealing the adhesive forces of the individual receptor-ligand bond changes in receptor group dynamics could also be monitored. This chapter presents the basic methodology for acquiring ligand–receptor force measurements, followed by a discussion on some recent applications and findings from these techniques. Modification of the typical AFM design used for imaging can improve the quality of the signal acquired in the AFM force measurements.