Custom Oligos

Custom siRNA Oligos

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High quality and cost-effective custom siRNA sequence synthesis available for your unique sequence or by using our in-house design service, utilizing the Rosetta Design Algorithm. Choose from a wide range of modifications, purifications and quantities to tailor to your specific needs.

Ready to order? Custom siRNA (2OD - 50OD) Click here.
Need our siRNA design service? Email

(Provide the gene symbol, refseq and species, or transcript to target for design, and the # of designs needed. Our bioinformatics dept. will provide siRNA sequences designed by our Rosetta design algorithm, and will return the results to you by email within 3 business days).


  • Variety of Modifications available
  • Deprotected, desalted and ready-to-use
  • µg to multi-gram capacity
  • Purified by HPLC, RPC (cartridge purified) PAGE or in vivo quality upon request
  • Free siRNA design available for a variety of species
  • Available in duplex or single-stranded form
  • Phosphodiester or Phosphorothioate backbones available
  • Comprehensive QC and technical data sheet provided with each siRNA
  • Rapid turn-around time and high throughput capacity


For siRNA we design, we guarantee that 2 out of 3 siRNA per gene will achieve knockdown of ≥75%.

Superior Manufacturing Capacity

With a capacity to synthesize over one million siRNA oligos per year, we offer reliable delivery times, no matter how many oligonucleotides you order.

RNA Chemistry and Proprietary Technology

Our RNA synthesis relies on the use of fast deprotection ribonucleoside phosphoramidites protected at the 2' position by a tert-butyldimethylsilyl (TBDMS) group and, at the 3' position, by a phosphoramidite.

RNA synthesis and deprotection are performed using our proprietary technology e.g., Ultra Fast Parallel Synthesis (UFPS) and Ultra Fast Parallel Deprotection (UFPD). The use of these technologies means higher coupling efficiency and faster deprotection, resulting in higher quality synthesis and faster turn-around times.

UNA (Unlocked Nucleic Acid) Modification

UNAs (Unlocked Nucleic Acid) are helix destabilizing, non-nucleotide analogues of RNA in which the bond between the C2’ and C3’ atoms is not present (see Figure 1). Incorporation of UNA results in considerable reduction in the RNA:RNA duplex melting temperature (Tm) while maintaining an A-form helical structure1.

Figure 1. General structure of UNA

Like LNA, UNA enables fine tuning of duplex thermodynamic stabilities. Their antipodal structural characteristics make UNA and LNA complementary with respect to effect on binding affinity towards a DNA or RNA target: Tm is decreased by 5-10°C per UNA monomer2; Tm is increased by 3-10°C per LNA monomer.

Specifications of siRNA Oligos


Quality control Individual strands are analyzed by mass spectrometry. Depending on manufacturing site, PAGE may be used to assess siRNA duplexes. siRNA quantity is systematically validated by UV absorbance at 260 nm.
Purification Fully deprotected and desalted
Purified by HPLC, RPC (cartridge), In vivo quality or PAGE upon request
Quantities offered
2 OD (~10 nmol), 5 OD (~25 nmol), 10 OD (~50 nmol), 50 OD (~250 nmol)—online
1-25 mgs, 50 mgs – 1 G Email
Length 19 to 45 mers
RNA, DNA, 2'OMe, UNA (Unlocked Nucleic Acid)
Backbone Phosphodiester or Phosphorothioate bond
Labels and modifications Amine, biotin, Cyanine-dyes, 6-FAM, fluorescein, phosphate. Other labels available upon request
Format Duplex siRNA oligos are delivered dry or liquid
Storage and stability Although oligonucleotides are stable in solution at 4°C for up to 2 weeks, we recommend storage at -20°C. Repetitive freeze-thaw cycles should be avoided by storing as aliquots. For long-term storage, siRNA oligos should be dried. Oligonucleotides with fluorescent labels should be protected from light. We guarantee our oligonucleotides for six months, when stored under the above conditions.
Shipment Shipped by express delivery, dry or liquid in individual, transparent tubes
Technical Data
Oligonucleotides are delivered with an Oligonucleotide Technical Data Sheet, which includes oligonucleotide name, sequence, concentration, precise quantity in OD and nmols, Tm, MW, size, extinction coefficient and purification data. Additional gel images are provided for duplex confirmation upon request.
Services available upon request Aliquoting
Free design support
Pricing Please contact your local sales representative or email us at
Ordering On-line, by email or by fax


  1. Langkjær, N., Pasternak, A. and  Wengel, J. (2009) UNA (unlocked nucleic acid): A flexible RNA mimic that allows engineering of nucleic acid duplex stability. Bioorg. Med. Chem., 17. 5420-5425.
  2. Nielsen P., Dreiøe L. H. and Wengel J. (1995) Synthesis and evaluation of oligodeoxynucleotides containing acyclic nucleosides Bioorg. Med. Chem., 3, 19-28.

Pasternak, A. and  Wengel, J. (2011) Unlocked Nucleic Acid – an RNA Modification with Broad Potential. Org. Biomol. Chem., 9. 3591-3597.

Bramsen, J.B., laursen, M.B., Nielsen, A.F. et al. (2009) A large-scale chemical modification screen identifies design rlues to generate siRNAs with high activity, high stability and low toxicity. Nucleic Acids Res., 37, 2867-2881.

Kenski, D.M., Cooper, A.J. et al (2010) Analysis of acyclic nucleoside modifications in siRNAs finds sensitivity at position 1 that is restored by 5’-terminal phosphorylation both in vitro and in vivo. Nucleic Acids Res., 38, 660-671.

Narendra Vaish, Feng Chen. (2010)  Improved Specificity of Gene Silencing by siRNAs Containing Unlocked Nucleobase Analogs. Nucleic Acids Research, 39-5 1823-1832.

Yang, X. et al. Gene Silencing Activity of siRNA Molecules Containing Phosphorodithioate Substitutions. ACS Chem Biol. 2012 Apr 18. [Epub ahead of print]

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siRNA Literature for Download

siRNA Users Guide by Tuschl et al.

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