Should I add 4FB or HyNic to my amino-modified oligo?

We have found that our Hynic oligos have a tendency to dimerize if not used immediately after modification. If you are planning on immobilizing the oligo on 4FB beads, if the Hynic oligo is added to the 4FB magnetic microspheres immediately after desalting, then you shouldn’t see too much dimerization. We have used this scheme before with success. For these reasons, for typical reactions, such as antibody-oligo conjugations, you want to modify your oligo with 4FB, not with HyNic.