Fluorescein isocyanate is a chemical substance used in various fields, such as biochemistry, molecular biology, fluorescence microscopy, and medical diagnostics. Fluorescein isocyanate binds covalently to proteins and other biomolecules, resulting in intense fluorescence that can be detected with specialized imaging equipment. Some synonyms for fluorescein isocyanate include fluorescein-5-isothiocyanate (FITC) and fluorescein O-isothiocyanate. FITC is a popular fluorescent dye used in bioanalytical assays and antibody labeling, while fluorescein O-isothiocyanate is mainly used for cell labeling and intracellular monitoring. Other related synonyms include fluorescamine, fluorescein diacetate, and fluorescein thiosemicarbazide. Fluorescein isocyanate and its synonyms have enabled significant advances in biomedical research and diagnostic applications.