Zinc in fixatives
The role of zinc in formalin-based fixatives was covered in detail in
my review article published in Biotechnic & Histochemistry
68(2):7582, 1993. To summarize very briefly, zinc functions in at
least 2 ways:
1. it prevents or at least inhibits crosslinking by formaldehyde, and
2. it apparently holds macromolecules in their native 3-dimensional
Together, this creates superior morphological detail at the level of
the light microscope, and allows the use of nearly any antibody
without having to resort to antigen retrieval or epitope recovery.
Tissues fixed in NBF take 24-48 hours to fix properly for good
morphology, but zinc formalin will produce the same level of quality
in 8 hours (for surgical specimens, less for biopsies).
Tissues can be stored in zinc formalin for weeks or months without
significant loss of immunoreactivity.
There are several formulations, and they do make a difference. The
most common is unbuffered zinc sulfate formalin which may produce
formalin pigment artifact in bloody tissues. Published formulations
generally cause precipitation of zinc salts inside tissues (making
them somewhat harder to section), and frequently make a mess inside
tissue processors (some processor manufacturers recommend against
zinc formalin for this reason). However, there are commercial
products that have gotten around both of those problems (see Anatech
and Shandon for further information) and these can be used in
Buffered zinc formalin avoids the formalin pigment problem, but it is
tricky to make since zinc precipitates at about pH 6.0. Commercial
products are generally stable.
Zinc chloride is sometimes used. It is faster, hardens tissues more
and cannot be used for storage. It is corrosive to metal and must
not be used on tissue processors.
Zinc salicylate has been used rarely, offers no advantage over other
zinc formulations, and is expensive (homemade or commercial). It is
available from Polysciences.
Further details, both purely techni
<< Previous Message | Next Message >>