fluorescein

Fluorescein is a synthetic organic compound used as a fluorescent dye. It belongs to the xanthene family and emits green fluorescence when excited with blue light. In neutral solution its absorption maximum is around 494 nm and its emission maximum near 521 nm; fluorescence increases with deprotonation, and the dye is highly water-soluble. The dye exists in several forms, including the neutral molecule and the disodium salt, which is commonly used in medical and laboratory applications. Fluorescein fluorescence is pH-dependent and can be affected by light exposure, making photobleaching a consideration in some uses.

Applications of fluorescein span medical diagnostics, research, and environmental tracing. In ophthalmology, sodium fluorescein is used topically to stain the ocular surface and to perform fluorescein angiography after intravenous injection, highlighting retinal vasculature. It helps assess tear film stability and detect corneal epithelial defects. In fluorescence microscopy and related techniques, fluorescein and fluorescein-labeled derivatives (such as FITC) label tissues and biomolecules for visualization in immunofluorescence, flow cytometry, and fluorescence in situ hybridization.

Beyond medicine, fluorescein serves as a tracer dye in environmental and industrial contexts, where it helps map water movement and dispersion in hydrological studies and engineering applications. Its bright fluorescence and well-characterized spectral properties make it useful in imaging and detection protocols.

Safety considerations include the potential for rare allergic or adverse reactions. Commonly, administration may cause temporary nausea, vomiting, or faintness, and urine or stools may appear yellow-green for a short period after use. Handling should minimize patient exposure to excessive light to reduce photobleaching and ensure proper disposal of contaminated materials.