Preparing biological specimens for the TEM, whilst retaining the structural morphology of the material is a challenge. However, researchers have been looking at biological material for many years and many protocols exist which allow us to look at biological material in many different ways. Whole mounts Small or very thin objects can be examined directly by mounting them onto a support film and introducing them directly into the electron beam.
Contrast is provided by heavy metal precipitation in one of three ways.
The specimen appears light on a dark background. More details can be found here . Rotary shadowing, where the specimen is uniformly coated with heavy metal is used to visualize nucleic acids and proteins. Often the sections are further contrasted with uranyl acetate and lead citrate prior to examination in the microscope. In some cases, macromolecules can be specifically labelled prior to embedding and sectioning.