Overview
Eosin Y is a brominated derivative of fluorescein and one of the most widely used counterstains in histology, particularly in Hematoxylin and Eosin (H&E) staining protocols. First synthesized in 1871, it selectively stains cytoplasmic components, collagen, and red blood cells pink-red. The dye's fluorescence properties make it valuable in modern biomedical research, including live-cell imaging and flow cytometry. As a tetrabromo compound, Eosin Y exhibits superior lightfastness compared to non-brominated dyes. Its anionic nature allows selective binding to positively charged tissue components. Commercial grades vary by purity (70–95%), with histological-grade products optimized for consistency in diagnostic applications.
Physical and Chemical Properties
Eosin Y demonstrates unique photophysical characteristics with an absorption maximum at 514–518 nm and emission peaking at 540–550 nm. The dye undergoes reversible dimerization in aqueous solutions above 10−4 M concentration, affecting its spectroscopic behavior. Its fluorescence quantum yield is approximately 0.19 in water but increases in less polar solvents. The compound shows marked pH sensitivity, transitioning from yellow (acidic) to red (neutral/alkaline) due to lactone ring opening. It forms insoluble eosin-metal complexes with cations like Pb2+ or Al3+, a property exploited in pigment manufacturing. Thermal decomposition occurs above 300°C without distinct melting.
Main Applications
In diagnostic pathology, Eosin Y is the standard cytoplasmic counterstain in H&E preparations, providing contrast to hematoxylin-stained nuclei. It differentially stains connective tissue (pink) and muscle fibers (deep red). The dye also serves in Romanowsky-Giemsa blood smears for malaria diagnosis. Research applications include fluorescent tracking of cell viability (dead cells uptake eosin), membrane permeability assays, and as a photosensitizer in photodynamic therapy. Industrial uses encompass red ink formulations, paper dyes, and as a colorant in cosmetics (restricted concentration). Recent studies explore its role in organic photovoltaics due to light absorption efficiency.
Safety and Storage
While Eosin Y has low acute toxicity (LD50 >2000 mg/kg orally in rats), it may cause eye/skin irritation and allergic reactions in sensitized individuals. Powder handling requires NIOSH-approved dust masks and chemical goggles. Spills should be contained with absorbent materials and cleaned with copious water. Long-term storage stability requires protection from humidity (use desiccants) and oxidation (amber glass containers recommended). Aqueous solutions remain stable for months at 4°C but should be filtered if precipitation occurs. Incompatible with strong oxidizers and concentrated acids.
B2B Procurement Guide
When sourcing Eosin Y, verify certification for intended use – histological grade (USP/BP) for medical applications versus technical grade for industrial purposes. Key specifications include dye content (typically 85–95%), heavy metal limits (<10 ppm), and solubility performance. Batch-to-batch consistency is critical for staining reproducibility. Leading manufacturers include Sigma-Aldrich, Thermo Fisher, and TCI. Bulk purchases (1kg+) may reduce costs by 15–30%. Request Material Safety Data Sheets (MSDS) and Certificate of Analysis (CoA) for regulatory compliance. Consider prepackaged staining kits for standardized workflows.
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