It has long been recognized that one of the major limitations in biolo
gical atomic force microscopy (AFM) is the softness of most biological
samples, which are easily deformed or damaged by the AFM tip, because
of the high pressure in the contact area, especially from the very sh
arp tips required for high resolution. Another is the molecular motion
present at room temperature due to thermal fluctuation. Using an AFM
operated in liquid nitrogen vapor (cryo-AFM), we demonstrate that cryo
-AFM can be applied to a large variety of biological samples, from imm
unoglobulins to DNA to cell surfaces. The resolution achieved with cry
o-AFM is much improved when compared with AFM al room temperature with
similar specimens, and is comparable to that of cryo-electron microsc
opy on randomly oriented macromolecules. We will also discuss the tech
nical problems that remain to be solved for achieving even higher reso
lution with cryo-AFM and other possible applications of this novel tec
hnique.