Oligo Modifications
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HRP for sensitive hybridization probes

Quick facts:

Availability: DNA and RNA

Location: 5′ and 3′

Scale: 250 nmol to mid-scale

Purification: HPLC required; PAGE is not recommended as it can impair enzyme activity

IDT ordering symbol:  This is a Non-Catalog modification. Please contact noncat@idtdna.com with your sequence design for review and quoting.

Horseradish Peroxidase, or HRP (Figure 1), is an enzymatically active glycoprotein that can be conjugated to an oligonucleotide via a maleimide attachment to form a thioester. In the presence of H2O2, this enzyme catalyzes an oxidation reaction that converts reduced, non-fluorescent or non-colorimetric substrates into oxidized, fluorescent or colorimetric forms [1].

Research shows that HRP directly conjugated to hybridization probes can increase signal amplification in Catalyzed Reporter Deposition-Fluorescent In Situ Hybridization (CARD-FISH) protocols [2]. This modification can also be used in nonradioactive immunoassays, northern/Southern blot analysis, and other in situ hybridization applications.

Figure 1. 5′ HRP modification.
(Note that the 3′ HRP modification uses a 3 carbon thiol linker arm.)

Submitting requests for HRP-oligos

Synthesis of HRP-modified oligos requires special chemistry; therefore these sequence designs must undergo review and quoting prior to synthesis.  IDT scientific experts meet regularly to review the complexity and feasibility of producing nonstandard sequence requests including oligos containing HRP modifications. 

Please direct inquiries to noncat@idtdna.com with your contact information and requested sequence, including any additional modifications or yield requirements.


  1. Akkara JA, Senecal KJ, Kaplan DL (1991). Synthesis and characterization of polymers produced by horseradish peroxidase in dioxane. J Polymer Sci 29(11):1561–1574. doi:10.1002/pola.1991.080291105.
  2. Dijk JA, Breugelmans P, et al. (2008). Catalyzed reporter deposition-fluorescent in situ hybridization (CARD-FISH) detection of Dehalococcoides. J Microbiol Methods 73(2):142–147. doi: 10.1016/j.mimet.2008.01.012

Additional reading

Need a non-standard modification?—Review a list of the common modifications IDT can add to oligonucleotides here. Not finding a modification you need on the IDT website? No worries. 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 send a request to noncat@idtdna.com

Improving Immuno-PCR by Optimizing Antibody-Oligo Conjugation—Immuno-PCR, a modified antigen detection method, uses an antibody coupled to DNA, which is then amplified using real-time PCR. The method can significantly increase antibody-target detection sensitivity by 100–10,000X over standard ELISA assays. Innova Biosciences provides both a kit and a service to generate the antibody-oligonucleotide conjugates, and affirms that the high quality of IDT oligos provides optimal conjugation.

Fluorescent Dyes With No Licensing Restrictions—A Growing Portfolio—Learn about fluorescent dyes that are suitable for commercial and diagnostic applications and that have no patent licensing restrictions. Access a table of Freedom Dye alternatives here.

Author: Amanda Bowersox is a research scientist at IDT. 


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