C. Zobel, M. Beer
International review of cytology
Publisher Summary A method for the identification of various regions in the object may be done by increasing the mass of local regions in the object by the selective attachment of suitable reagents, called electron stains. To identify the chemical nature of various components of the object, a number of methods for selectively increasing their mass have been tried. The chapter reviews these methods such as: direct attachment of heavy metals, attachment of organic reagents or organic reagents substituted with heavy metals, precipitation of antibodies by their homologous antigens, and precipitation of heavy metals by the products of enzymic reactions. A satisfactory stain must fulfill two requirements: First, it must increase the local electron-scattering power of the specimen sufficiently so that an appreciable increase in image contrast results. Second, it must show suitable selectivity so that its localization. This chapter focuses on the use of heavy metal salts as selective reagents to reveal compositional differences in the object under study. The relevant factors for consideration are the selectivity exhibited by the various reagents when used as stains, the amount of material bound, and the resultant increase in contrast in local regions of the electron micrographs. Consideration of selectivity requires analysis of the various factors which affect the specificity of binding such as pH, temperature, concentration of the staining solution, and the effects of fixation and embedding.