In histochemistry and cytochemistry, horseradish peroxidase-labeled lectins are often used as probes for the localization of carbohydrates in cells and tissues. In transmission electron microscopy, the most commonly used procedure for detection of carbohydrates is lectin–gold labeling. Horseradish peroxidase catalyzes the formation of insoluble polymerized diaminobenzidine which on exposure to osmium tetroxide forms osmium black, a compound visible in the electron microscope, making horseradish peroxidase an alternative to the more frequently used colloidal gold. This chapter describes a pre-embedding method for carbohydrate localization in which tissue sections are incubated with horseradish peroxidase-conjugated lectin prior to embedding in resin.
