why is glutaraldehyde used for SEM sample fixation rather than formalin?

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Abe
Abe's picture
why is glutaraldehyde used for SEM sample fixation rather than formalin?

A colleague asked me why we use glutaraldehyde for SEM samples and formalin for histological samples, and I didn't have a good answer. Is this just historical or are there technical differences between the methods. Doesn't glutaraldehyde cross-linking have effects that can show up as artifacts for SEM?

Dan Dwyer
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The reason for using

The reason for using glutaraldehyde versus formaldehyde lies in the "strength" of the fixation reaction. Glutaraldehyde is a more gentle fixative which is less likely to distort membrane and cytoskeletal proteins and their ultrastuructural prsentation in and on the cell. It still provides the needed cross-links to fix the sample but it doesn't cross-link so heavily that the structures assume an unnatural shape. Formaldehyde is quite a strong cross-linking fixative and at the higher levels of magnification used in SEM, and especially TEM, can cause obvious distortion of cellular structures. This can especially be seen if glutaraldehyde, formaldehyde and flash-frozen samples are compared.

Depending on the study being undertaken with SEM, it may be possible to use formaldehyde, but better preservation of ultrastructural features such as microvilli are obtained with glutaraldehyde.

Hope this helps.

Lubrol

Abe
Abe's picture
Thanks for the explanation.

Thanks for the explanation.

Abe