The Transmission Electron Microscope
- Preparation of
In a TEM, the specimen you want
to look at must be of such a low density that it
allows electrons to travel through the tissue. There
are different ways to prepare your material for that
purpose. You can cut very thin slices of your
specimen from a piece of tissue either by fixing it
in plastic or working with it as frozen material.
Another way to prepare your specimen is to isolate it
and study a solution of for example viruses or
molecules in the TEM.
You can also stain the specimen
in different ways and use markers to locate specific
things in the tissue. It can for example, be stained
with heavy metals like uranium and lead, which
scatters electrons well and improves the contrast in
Below are two examples
described in more detail.
1. Sections of
material contains large quantities of water. Since
the TEM works in vacuum, the water must be removed.
To avoid disruption as a result of the loss of water,
you preserve the tissue with different fixatives.
These cross-link molecules with each other and trap
them together as stable structures. The tissue is
then dehydrated in alcohol or acetone.
After that, your specimen can
be embedded in plastic that polymerize into a solid
hard plastic block. The block is cut into thin
sections by a diamond knife in an instrument called
ultramicrotome. Each section is only 50-100 nm
The thin sections of your
sample is placed on a copper grid and stained with
heavy metals. The slice of tissue can now be studied
under the electron beam.