Used primarily in histology and pathology to stain acidic polysaccharides such as glycosaminoglycans (GAGs) in tissues. It is especially effective for visualizing mucins in epithelial cells, cartilage, and connective tissues. Commonly applied in the identification of mucin-producing tumors, assessment of basement membranes, and evaluation of cartilage degradation in joint diseases. Works best at low pH (2.5) where it selectively binds to carboxyl and sulfate groups of acidic mucins. Often used in combination with other stains like periodic acid-Schiff (PAS) to differentiate types of mucins in tissue sections. Also utilized in cytology for detecting mucin in cell smears.