Modifications are divided into the following groups:

However, internal or 5'-position modifications can also be inserted at the 3' end of an oligonucleotide using special procedures. Please inquire.

If the modification you require is not shown on the list below, please contact us, as we have experience in incorporating a wide range of both commercial and custom modifications.


Internal or 5’ redundancies are made without additional charges. We only charge extra for 3’ redundancies. Redundancies or mixed base positions are indicated using the ambiguity table from International Union of Biochemistry.

M (AC) Y (CT) D (AGT)
R (AG) K (GT) B (GCT)
S (CG) H (ACT)    


Doped oligonucleotides are described by inserting numbers (1, 2, 3, 4, 5, etc.) in the sequence in the doped positions. Each number, then, may refer to a specific kind of doping specified by you or one of the following doping types.


90% G + 3.3% each of A, C and T


70% A + 20% G + 5% each C and T


80% A + 20% dInosine

(Please note exact specification in your order.)

Each doping type may occur in several positions within the oligonucleotide sequence, e.g., the oligonucleotide contains 3 different doping types.

5'-TG1 2TT 1GA TA3 CCC TC 123 TT-3'