Hematoxylin and eosin
Elastic fiber stain
Reticular fiber stain
Transmission and Scanning Electron
In slightly over 60 years,
has gone from a scientiF
c curiosity to an essential tool in the study of tis-
sue structure. The general steps used in TEM are conceptually similar to those used in light microscopy
but customized to meet the unique needs of this technique. The tissue blocks are quite small, usually
about 1 cubic millimeter, specially F xed to retain the F
ne integrity of the cellular constituents, and inF l-
trated with unpolymerized plastic rather than with wax or ﬂ
uid. Sections usually in the range of 0.02 to
m are cut using a knife fashioned from glass or diamond (steel cutting edges are not used in TEM).
These tiny thin sections can be treated with solutions of heavy metal salts, such as lead citrate or uranyl
acetate, to enhance contrast of the section. These salts become deposited on different structures within
the cell making them electron dense, and they appear darker in electron micrographs. Once treated, the
sections are mounted on perforated copper grids and the grids inserted into an electron microscope.
A beam of electrons passes through the section, creating an image that can be viewed on a ﬂ
plate and used to create a negative or digital image.
Scanning electron microscopy
is similar, in many aspects, to TEM methods, except that small
pieces of tissue are specially coated with a thin layer of gold or palladium. Sometimes, the tissue is
frozen and then fractured to reveal internal structure before the metal-coating step. The electron beam
passes over the surface of the specimen, and the metallic coating reﬂ
ects some of these electrons. The
reﬂ ected electrons are detected and are used to create a three-dimensional image of the surface of the
specimen. Such images can be recorded as negatives or digital images.
Transmission electron microscopy (TEM)
Scanning electron microscopy (SEM)