Biological AFM: where we come from--where we are--where we may go.

Biological atomic force microscopy (AFM) is a fast growing and advancing field. This review's objective is to overview the state of the art and to retrace achievements of biological AFM as presented by past and present research, and wishes to give a (subjective) outlook where AFM may go in the upcoming years. The following areas of interest are discussed: High-resolution imaging, cell imaging, single molecule force spectroscopy, cell mechanical measurements, combined AFM instrumentation, and AFM instrumentation. Of all these topics, particular representative examples are shown, each of them standing for a variety of achievements by many research groups.