CRYO ATOMIC-FORCE MICROSCOPY - A NEW APPROACH FOR BIOLOGICAL IMAGING AT HIGH-RESOLUTION

A low-temperature atomic force microscope (cryo-AFM), operated in liqu id nitrogen vapor, has been constructed for biological applications. T he system provides an adjustable imaging temperature from 77 to 220 K with atomic resolution achieved on crystalline specimens. Imaging with NaCl microcrystals demonstrates that the system is free from surface contamination. Below 100 K, several biological specimens, including im munoglobulins and DNA as well as red blood cell ghosts, were imaged at high spatial resolution. Measurements on individual macromolecules sh owed that the mechanical strength is significantly greater at cryogeni c temperatures with an estimated Young's modulus 1000-10 000 times tha t of a hydrated protein at room temperature, providing a solid basis f or future improvements and applications of cryo-AFM in structural biol ogy.