eosina

Eosin, known in Spanish as eosina, refers to a group of synthetic acidic dyes in the xanthene family. The most commonly used forms are eosin Y and eosin B, typically supplied as disodium or tetrasodium salts. They are water-soluble anionic dyes whose color ranges from pink to red under standard light, and certain preparations can exhibit fluorescence under ultraviolet light.

In histology, eosin is employed as a counterstain to hematoxylin in routine staining protocols. Hematoxylin stains nuclei blue to purple, while eosin stains the cytoplasm, connective tissue, collagen, muscles, and other eosinophilic structures pink to red. The staining is pH-dependent; eosin binds more readily to basic or positively charged cellular components. In many laboratories, eosin Y is used in the standard hematoxylin-eosin (H&E) procedure, and eosin-based dyes appear in some polychromatic stains for cytology, including certain Pap stain formulations.

Applications extend beyond H&E; eosin dyes are used in cytology, histochemistry, and some microbiology contexts as general counterstains. Because of their fluorescence, eosin compounds can also be used to label specimens under fluorescence microscopy, though this is less common in routine histology.

Safety and handling: Eosin solutions are irritants; they should be handled with gloves and eye protection, and waste disposed of according to local chemical waste regulations. In storage, eosin salts are typically kept dry and protected from prolonged light exposure to minimize bleaching.