6-Carboxyfluorescein (6-FAM) is a fluorescent dye with an absorption wavelength of 495 nm and an emission wavelength of 517 nm. A carboxyfluorescein molecule is a fluorescein molecule with a carboxyl group added. They are commonly used as a tracer agents. It is used in the sequencing of nucleic acids and in the labelling nucleotides.
Commercially available FAM is a mixture of two isomers, 5-FAM and 6-FAM, and the correct name is 5(6)-carboxyfluorescein.
The dyes are membrane-impermeant and can be loaded into cells by microinjection or scrape loading. It can be incorporated into liposomes, and allow for the tracking of liposomes as they pass through the body. In addition, carboxyfluorescein has been used to track division of cells.
Popular derivatives for cell tracing purposes are Carboxyfluorescein diacetate succinimidyl ester (CFDA-SE) and Carboxyfluorescein succinimidyl ester (CFSE).