SPI-Mark™ Colloidal Gold Reagents
Embedding
Tissues may be embedded in different types of resin for EM applications. In
either case the embedding should allow good preservation of the antigens of
the antigens without sacrifice of structural information. Generally there are two
types of resin, epoxy resins (e.g. Araldite, Epon), which have an aromatic ring
structure and are strongly cross linked, and acrylic resins (e.g. UNICRYL),
which have a lower cross linking. Epoxy resins are hydrophobic whereas
acrylic resins may be hydrophobic or hydrophilic.
The best structural preservation and stability is provided by epoxy resins while
the best immunolabeling is achieved with acrylic resins. This is because
acrylic resins, especially UNICRYL, cut in such a way as to reveal the proteins
at the section surface and they also wet more easily, thus giving greater
accessibility to the antibodies during subsequent incubations. For optimal
results a compromise must be reached and the usual choice is a polar (i.e.
hydrophilic) resin with moderate cross linking. UNICRYL, manufactured by BBI,
gives excellent immunolabeling characteristics together with a high degree of
stability and structural preservation. UNICRYL allows the embedding
procedure to be performed at low temperatures. This ensures that vital
components are not extracted during dehydration and that no excessive
temperature rise occurs during polymerisation, which may damage the tissue antigens.
For LM applications tissues may be embedded in acrylic resins such as
UNICRYL as described above, or in paraffin wax. Resin embedded sections
provide very high resolution of labeling but only allow labeling of those
proteins at the surface. Wax embedded sections permit the whole depth of the
section to be labelled when dewaxed. Where high temperatures must be
avoided cryosections can sometimes be used for immunolabeling for LM
studies.
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Thursday May 17, 2012
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