Frozen Section Embedding Medium

Frozen sectioning is a cryostat-based tissue preparation method in which fresh, fixed, or cryoprotected tissue is rapidly frozen, embedded in a support medium such as OCT, cut into thin cryosections, and mounted on slides for rapid morphology, histochemistry, immunofluorescence, in situ hybridization, enzyme activity, lipid, mucin, or downstream molecular analysis. The method preserves antigenicity and avoids dehydration/clearing steps used in paraffin processing, but frozen sections are physically less stable and generally show more freezing or cutting artifact than FFPE sections; therefore, frozen sectioning is useful for rapid diagnosis, spatial molecular assays, and preservation of labile targets, but not always optimal for fine morphology alone.

Immunohistochemistry-Frozen (IHC-F) of frozen samples is a widely used technique for detecting and locating specific antigens within preserved cellular structures. Unlike formalin-fixed paraffin-embedded samples, frozen tissues retain their natural antigenicity, making them particularly suitable for targets sensitive to chemical fixation, and the procedure is relatively simple and rapid.

Polymer-based two-step IHC detects tissue antigens by first binding an unlabeled primary antibody to the antigen and then applying an HRP-polymer secondary reagent that carries multiple secondary antibodies and HRP molecules on a polymer backbone; the localized HRP converts chromogens such as DAB or AEC into visible deposits for light-microscopic interpretation. The method is \"two-step\" because the primary antibody step is followed directly by the polymer-enzyme secondary reagent, rather than by separate secondary-antibody and avidin-biotin complex steps; published comparisons reported similar or higher sensitivity than several multistep systems and avoidance of endogenous-biotin interference.

Avidin-biotin or streptavidin-biotin immunohistochemistry detects tissue antigens by binding a primary antibody to the target antigen, then detecting that antibody with a biotinylated antibody and an avidin-biotin-enzyme or streptavidin-enzyme detection complex; the enzyme reaction produces a visible chromogenic deposit at the antigen site for light-microscopic localization. The classic ABC method uses the high-affinity avidin-biotin interaction to bridge biotinylated secondary antibody and biotinylated peroxidase, and early comparative studies reported stronger immunoperoxidase staining than PAP-based methods in formalin-fixed tissue sections.

Frozen-section immunofluorescence/immunohistochemistry detects antigens in cryosectioned tissue using primary antibodies and fluorescent or enzyme/fluorophore-linked detection reagents, allowing spatial localization of proteins or other antibody-recognized targets in preserved tissue architecture. Frozen tissue is useful when markers are poorly compatible with FFPE processing, and multiplex fluorescence can detect several markers on one frozen section.