Tissue preparation snap-freezing

Air drying, usually with subsequent chemical post-fixation, is applicable for cell smears, cytospins and cryosections. Snap freezing (usually in liquid nitrogen) is routinely employed for tissue probes for subsequent cryosectioning. Chemical fixation is commonly carried out in aldehydes (e.g. formaldehyde) for tissue probes and cultured cell monolayers, and in acetone or alcohols (methanol or ethanol) for cryosections and cell preparations. 

Those interested in using immunohistochemistry to study apoptosis need to consider the method of tissue preparation and fixation. Since many antibody epitopes do not survive formalin/glutaraldehyde fixation or paraffin embedding, investigators should determine under what conditions the antibody of interest will work prior to sample collection. There are antibodies that will successfully bind to formalin-fixed, paraffin-embedded material, but if the investigator is unsure, fresh snap-frozen samples can be used to optimize conditions for success since freezing generally will not alter epitopes. 

Snap freezing - widely used term to describe freezing tissue for immunocytochemistry the term comes from food preparation industry and for biomedical sciences it has no single definition and can mean freezing in liquid nitrogen, on dry ice, or in isopentane. 

Recent observations by Svensson et al. (29) point toward post-mortem changes in the proteome of susceptible peptides and proteins within minutes. To prevent these alterations of the sample Svensson et al. use focused microwave irradiation to sacrifice the animals. Since focused microwave irradiation is not available in every laboratory, an alternative way to minimizing alterations is snap-freezing of the dissected tissue and defrosting only just before sample preparation starts. 

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