Fluorescein

Fluorescein is a synthetic organic compound belonging to the xanthene dye family, with the formula C20H12O5 and a molar mass of 332.3 g/mol. It appears as a dark orange/red crystalline powder, slightly soluble in water and more soluble in alkalis, and exhibits intense green fluorescence under ultraviolet or blue light due to its unique quinonoid or lactone structure. Fluorescein and its sodium salt (fluorescein sodium or uranine) are extensively used as fluorescent tracers in cell and molecular biology, immunology, microscopy, and as a diagnostic agent in ophthalmology—for instance, to detect corneal abrasions or during retinal angiography. Its fluorescence is highly pH-dependent, making it useful for assays requiring pH sensitivity. It is also used in environmental tracing, forensics, and as a color additive. Fluorescein is not a molecular therapeutic target but rather a tool molecule in diagnostics and research.

Other names

D&C Yellow No. 7Solvent Yellow 94CI 45350:1Uranine (when in disodium salt form)Resorcinolphthalein3',6'-dihydroxyspiro[isobenzofuran-1(3H),9'-[9H]xanthen]-3-oneFluorescein sodium (for the disodium salt)