Orcein [1400-62-0]

Orcein is a natural dye derived from lichen species, composed of a mixture of phenazone compounds that bind to chromatin through electrostatic and hydrophobic interactions at acidic pH. For fluorescence microscopy, orcein solutions exhibit emission peaks at 587 nm at low concentrations and 620 nm at high concentrations, with stained chromatin showing an emission peak at 585 nm and a shoulder at 620 nm. In light microscopy, acetic orcein remains a standard method for visualizing polytene chromosome banding in Drosophila salivary glands, enabling high-resolution analysis of interphase chromatin structure after endoreplication. Additionally, orcein selectively stains elastic fibers and has been used to evaluate fibrosis quality in liver tissue, where its staining pattern helps distinguish progressive from regressive fibrosis.