There are many ways of preparing specimens for electron microscopy. The EMP staff are available to help investigators determine the best way of getting the information they need from their specimens.
In life science, specimen preparation methods perform the task of stabilizing the initially hydrated molecule, so that it can be placed and observed in the vacuum of the electron microscope. Biological specimens are typically prepared using
negative staining or
cryo-fixation (vitrification) techniques.
1.- Negative Staining
The contrast produced by the molecules itself is normally insufficient for direct observation in the electron microscope and a contrasting method has to be used. Negative Staining with heavy metal salts such as uranyl acetate produce high contrast and protects the molecule from collapsing. Instead of the molecule (with its interior density variations) only a cast of exterior surface of the molecule is imaged, and only its shape can be reconstructed.
2.- Cryo-fixation (vitrification)
Cryo-fixation is a method to “sustain” the molecule in a medium that closely approximates the aqueous environment. The samples are embedded in vitreous ice and we can obtain images of fully hydrated macromolecules (“Frozen-hydrated”). The vitrification process enables the structure of macromolecules and the cellular architecture to be studied in a frozen hydrated near native state. For preparing the cryo-samples a VITROBOT (FEI) is available.