Fluorescein

**Semantic type:** Indicator, Reagent, or Diagnostic Aid|Organic Chemical

**Definition:** An organic compound that has wide use as a synthetic coloring agent. It is prepared by heating phthalic anhydride and resorcinol over a zinc catalyst, and it crystallizes as a deep red powder. This agent emits an intense green fluorescence in the presence of alkaline solutions and therefore is used as a label when conjugated to antibodies or as a contrast agent for ophthalmic angiography.

**Synonyms:** - FLUORESCEIN