FIGURE 4-30 Metal shadowing makes surface details on very small objects visible by transmission electron microscopy. (a) The sample is spread on a mica surface and then dried in a vacuum evaporator (step 1). The sample grid is coated with a thin film of a heavy metal, such as platinum or gold, evaporated from an electrically heated metal filament (step 2). To stabilize the replica, the specimen is then coated with a carbon film evaporated from an overhead electrode (step 3). The biological material is then dissolved by acid and bleach (step 4), and the remaining metal replica is viewed in a TEM. In electron micrographs of such preparations, the carbon-coated areas appear light—the reverse of micrographs of simple metal-stained preparations, in which the areas of heaviest metal staining appear the darkest. (b) A platinum-shadowed replica of poliovirus particles.

[Part (b) Science Source]