NEW POSSIBILITIES IN THE OBSERVATION OF NUCLEIC-ACIDS BY ELECTRON SPECTROSCOPIC IMAGING

The conditions for the use of Electron Spectroscopic Imaging (ESI) in the observation of DNA molecules adsorbed on carbon film are described. The Zeiss 902 electron microscope with its built-in spectrometer allows original modes of imaging, such as energy-filtered annular dark-field. The six different modes of imaging are illustrated with either positively stained or metallized DNA preparations to show the resulting important differences in contrast. The very strong contrasts obtained in annular or spectroscopic dark-field modes on specimens presenting a very low contrast in traditional bright-field are very useful for the observation of biological macromolecules. The advantages of some observation modes for imaging different types of preparations are discussed.