Biological applications of atomic-force microscopy

Atomic force microscopy (AFM) has been successfully applied to image many biological specimens such as proteins, DNA molecules, membrane fragments, synthetic lipid bilayers and monolayers and even whole cells, with a resolution ranging from hundreds of nm to sub-nm. In particular, AFM has a unique capability of operating in solutions; thus, proteins in situ can be directly imaged to study their functional relationships to the structure. Because in AFM, the contrast reflects direct force interactions between the probe and the specimen surface, the resolution of AFM images is highly dependent on the specimen being studied. We, and others, found that atomic resolution images on hard crystal surfaces are among the easiest to be obtained in AFM. For example, periodic surface atomic structures with hexagonal, rhombohedral, and cubic lattices were clearly resolved by AFM [9-12]. Using the NanoScope II AFM with various home-made accessories, such as motion stages and fluid cells, we have studied several different biological materials with a resolution from tens of nm to subnm.