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Need a non-standard modification?

Need a modification you don’t find on our website? IDT offers 89 modifications that are not listed in our online catalog. A few of the more popular ones are described along with information on how to order them. IDT will consider any modification you have in mind. Just make a request at

Not finding the modification you need on the IDT website? No worries. IDT currently offers 89 modifications that are not listed in our online catalog. We have experience synthesizing these “off-catalog modifications”, but they are not in high demand like our 209 catalog options (see the below sidebar, Standard IDT Oligonucleotide Modifications, for a summary of those listed on our oligo modification catalog page).

The main difference between catalog and off-catalog modifications is that off-catalog modifications are not typically kept in stock. Therefore, these special modifications need to be prepared prior to oligonucleotide synthesis. This may increase turnaround time by 1–3 business days.

Off-catalog modifications we can synthesize for you

Here are a few examples of the off-catalog modifications we can provide:

Internal NHS ester modifications. We can provide several internal NHS ester modifications as off-catalog orders (Table 1). All internal NHS ester modifications are attached post synthesis to an amino modifier, C6 dT. Thus, such modifications will require a dT base at the position modified in your final oligo (for further explanation, see the article, When dT is required for modification attachment).

Table 1. Modification codes for off-catalog NHS esters.

Off-Catalog Modification Modification Code
DIG NHS ester /iDigN/
Cy® 5 NHS ester /iCy5N/
Cy® 3 NHS ester /iCy3N/
Most Alexa Fluor® Dye NHS esters Varies*

* For Alexa Dye mod codes, contact IDT Customer Care via web chat, phone (800-328-2661), or email (

Representative internal NHS Ester modifications

Digoxigenin NHS ester.

Figure 1. Internal DIG NHS Ester.

Dibenzocyclooctyl (DBCO). DBCO (Figure 2) is used for copper-free click reactions. We can place this modification on the 5′ or 3′ ends of an oligo. To order, use the 5′ modification code /5DBCON/, and the 3′ modification code /3DBCON/.

Figure 2. Dibenzocyclooctyl (DBCO).

DBCO-TEG, (Figure 3), offers a longer linker arm and is available for modification of the 5′ end of oligos; to order, use the 5′ modification code /5DBCOTEG/.

Figure 3. Dibenzocyclooctyl (DBCO)-TEG.

Puromycin. We can synthesize oligos with puromycin on the 3′ end (Figure 4). This modification is an antibiotic that mimics transfer RNA (tRNA). It is commonly added to the end of RNA oligos to facilitate binding in the ribosome’s A site. From there, it can attach to the growing peptide to ultimately stop elongation. Order this modification using the code /3Puro/.

Figure 4. Puromycin.

How to order off-catalog modified oligos

The codes used to order off-catalog modifications can be obtained from our Customer Care department. Contact them via web chat, phone (800-328-2661), or online using our IDT Help Request Form. Once you receive the modification codes for your off-catalog modifications, you can order them through the website just like standard catalog modifications. These oligos receive yield guarantees, and pricing will be provided in the website shopping cart.

IDT will consider any modification you have in mind. Please make such inquiries to

Standard IDT oligonucleotide modifications

You can find a list of 209 standard modifications we make to oligonucleotides on the Modifications page of our online catalog. These include modifications of the following types:

  • Phosphorylation
  • Spacers
  • Fluorophores
  • Iowa Black® Dark Quenchers
  • Dark Quenchers
  • Attachment Chemistry / Linkers
  • Modified Bases
  • Phosphorothioate Bonds
  • Click Chemistry

Published Mar 5, 2015
Revised/updated Nov 2, 2017