What is an AFM?

The Atomic Force Microscope (AFM) is a highly sensitive device suited to measure very small forces, down to several pico-Newtons (pN). It is highly versatile and can thus be used for many applications, including surface analysis, force mapping and force spectoscopy. Its working principle is quite simple: a tiny cantilever made of Si₃Ni₄ is mounted onto a piezo elment. A laser is focused on the cantilever and reflected towards a quadrant photodiode, which mesaures the deflection of the cantilever. Every cantilever has a certain stiffness and by Hooke's Law, the deflection can be translated into force:

F = -k * x

Applications in Cell Biology

Martin Benoit and Hermann E Gaub pioneered the field of cell-cell adhesion forces in the late '90s. Cell-cell forces can be measured quite accurately with an AFM. In these applications the cantilever surface is functionalized with a adhesive to immobilize the cell. Another cell is then approached from the top and after a certain contact time the cells are detached and the forces required for de-adhesion are recorded.

Another application is force mapping: A thin tip on top the cantilever is employed to scan adherent cells in a petri dish. The cantilever deflection correlates to the cell's viscoelastic properties.