fluorescéine

Fluorescein, commonly used in its sodium salt form (disodium fluorescein), is a synthetic xanthene dye that emits bright green fluorescence when excited by blue light. It is water-soluble and exists in equilibrium between a nonfluorescent lactone form (acidic conditions) and a highly fluorescent open-chain form in neutral to basic conditions. The dye is widely used in medical and environmental diagnostics.

Optical properties include an excitation maximum near 494 nm and emission around 521 nm. Fluorescence is pH-dependent, increasing as the dye opens from the lactone form; photobleaching can occur with prolonged exposure to light.

In ophthalmology, fluorescein is applied as eye drops or administered intravenously for fluorescein angiography to visualize retinal vessels. It stains the tear film to assess corneal integrity and helps detect ulcers. It is also used as a tracer dye in hydrology and, in surgery, to delineate tissues and perfusion.

Safety considerations: adverse reactions are uncommon but can include nausea, dizziness, or allergic responses. Urine and skin may take a yellow-green color for a day or two; contact lenses can be stained. Regulatory use exists in many countries; standard precautions apply and injections should be performed by trained personnel.

History: Fluorescein was developed in the 19th century, with Adolf von Baeyer describing its synthesis in 1871. It has since become a standard tool in clinical imaging and environmental tracing.