Introduction to atomic force microscopy.

Atomic force microscopy (AFM) is an invaluable tool not only to obtain high-resolution topographical images, but also to determine certain physical properties of specimens, such as their mechanical properties and composition. In addition to the wide range of applications, from materials science to biology, this technique can be operated in a number of environments as long as the specimen is attached to a surface, including ambient air, ultra high vacuum (UHV), and most importantly for biology, in liquids. The versatility of this technique is also reflected by the wide range of sizes of the sample that can dealt with, such as atoms, molecules, molecular aggregates, and cells. Indeed, this technique enables biological problems to be tackled from the single-molecule point of view and it allows not only to see but also to touch the material under study (i.e., mechanical manipulation at the nanoscale), a fundamental source of information for its characterization. In particular, the study of the mechanical properties at the nanoscale of biomolecular aggregates constitute an important source of data to elaborate mechano-chemical structure/function models of single-particle biomachines, expanding and complementing the information obtained from bulk experiments.