ELECTRON CRYOMICROSCOPY OF GRAPHITE IN AMORPHOUS ICE

Embedding biological macromolecules or molecular assemblies in amorphous ice provides natural surroundings for them which probably leaves their structure intact. However, it has been difficult in practice to get high-resolution information from such non-conducting, beam-sensitive samples. In this work graphite embedded in amorphous ice in the presence of detergent was used to investigate whether image degradation occurs also with a beam-insensitive object. Lattice images showing the 0.34 nm spacing were obtained but the choice of imaging conditions was important in determining the success rate. The best results were obtained using spot-scan with a beam diameter of 150 nm, under conditions which minimize the effects of charging of the specimen. Thus there is no intrinsic problem to obtaining high-resolution images of an object due solely to being embedded in amorphous ice. It should therefore be possible to get high-resolution information from biological objects, if the problem of charging can be overcome.