FAM is the most commonly used fluorescent dye for oligonucleotides attachment. It exhibits high quantum yields and it is compatible with most fluorescence detection equipment. Since it has decreased fluorescence below pH 7 it is typically used in the pH range 7.5 - 8.5.
There are two isomer derivatives of FAM (carboxyfluorescein): 5-FAM and 6-FAM. By default, Eurogentec uses 6-FAM for oligonucleotide labelling.
3’ 6-FAM allows effective blockage of the 3’terminus from polymerase extension as well as exonuclease digestion.