11 - Electron Microscopy of Isolated Virus Particles and Their Components

Abstract

Publisher Summary This chapter focuses on the electron microscopy of isolated virus particles and their components. The choice of supporting film or substrate depends on the type of specimen it has to carry. The choice is very often a compromise between film thickness, stability, and the amount of material deposited on the support. It is a general practice to use either Formvar [poly(vinyl Formol)] or collodion (nitrocellulose) dissolved in a suitable volatile solvent for plastic films. Films of collodion or Formvar can be cast on a distilled water surface or spread onto a cleaned glass surface. Carbon-supporting films have the important advantages of being relatively thin and are stable in the electron beam. However, a serious limitation is encountered in the structure resulting from contrast effects superimposed on the structure of the specimen. This is particularly noticeable in instruments capable of very high resolution. The extreme thinness of the object required for very high resolution may be overcome by spreading the specimen over holes. The presence of suitable holes in the supporting film has the additional advantage of indicating the level of focusing and astigmatic error. One of the earliest and most successful methods for enhancing the contrast in isolated particles for electron microscopy was the technique of shadow casting. The advantages of the shadow-casting procedure are two-fold. Contrast in the specimen is considerably improved, and a three-dimensional appearance to the specimen is introduced.