Eosine is a widely recognized synthetic dye, noted for its distinctive vibrant red or pink color. This compound is used across various scientific and industrial fields due to its strong staining properties and visual appeal.
What is Eosine?
Eosine is a fluorescent xanthene dye, specifically a brominated derivative of fluorescein. Its chemical name is 2′,4′,5′,7′-Tetrabromofluorescein disodium salt, and its molecular formula is C20H6Br4Na2O5. When exposed to ultraviolet (UV) light or visible light, eosine emits fluorescence in the red to orange-red range, enhancing contrast and visibility in stained specimens.
The dye appears as a dark red to maroon powder or crystals, which dissolve in water or alcohol to create a vibrant pink-to-red solution. Eosine is an acidic dye, meaning it is negatively charged. This allows it to bind to basic, or positively charged, components within cells and tissues. This binding occurs electrostatically with basic amino acid residues in proteins, such as histidine, arginine, and lysine, found in the cytoplasm, collagen, and muscle fibers.
Common Applications
Eosine is commonly used as a counterstain in histology, particularly in the hematoxylin and eosine (H&E) staining technique. In H&E staining, hematoxylin stains cell nuclei blue or purple, while eosine stains the cytoplasm and extracellular matrix various shades of pink or orange-pink. This combination provides pathologists with detailed structural information, aiding in the identification of tissue types and morphological changes for medical diagnosis. Eosine Y, a common variant, is used in concentrations of 1% to 5% by weight in water or ethanol for this purpose.
Beyond microscopy, eosine is also used in the cosmetics industry. Its vibrant color makes it a suitable colorant for products such as lipsticks and blushes, where it contributes to their characteristic red and pink shades. It also finds application as a red dye in inks, though it can degrade over time, causing the color to shift. It also serves as a photosensitizer in organic synthesis and has been explored in medical diagnostics, including vitamin measurement in food and as a radioactive tracer in certain drugs.
Safety and Handling
When handling eosine, general safety precautions should be followed. Avoid ingestion, skin contact, and inhalation of the powder or solutions. Eosine can cause skin irritation and is a strong dye, leading to staining of skin and clothing. If skin contact occurs, wash thoroughly with soap and water.
For safe storage, keep eosine in a dry, tightly closed container, away from incompatible substances like strong acids, strong bases, and sources of ignition. Ensure proper ventilation where it is handled to prevent dust formation. Dispose of eosine and its containers according to local and national regulations, often at hazardous waste collection points.