Mountant

Mountant, or mounting medium, is a preparation used in light microscopy to affix a specimen to a glass slide and preserve it for observation. It serves to secure the sample, protect it from dehydration and pigment loss, and minimize optical distortion by matching the refractive index between the specimen, the coverslip, and the glass.

Mountants come in several forms. Aqueous or water-based media, such as glycerin or gelatin-based preparations, are commonly used for living cells or temporary mounts. Resinous or non-aqueous media, including Canada balsam, DPX, Permount, Entellan, and Eukitt, cure or harden to a firm, long-lasting mount. There are also water-soluble mounting media based on polyvinyl alcohol or similar polymers. For fluorescence work, antifade or anti-phade mounting media, such as Vectashield or ProLong, are used to reduce photobleaching and preserve signal.

Application typically involves placing a small amount of mountant on the slide, positioning a coverslip over the stained or unstained specimen, and allowing the medium to set, cure, or evaporate as appropriate. Sealing the edges with nail polish or a specialized sealant can extend longevity.

Choice of mountant depends on sample type, staining method, fluorescent requirements, desired permanence, and storage conditions. Some mountants are optimized for rapid mounting and clearing, while others prioritize long-term preservation and refractive index compatibility with high-resolution microscopy.