HTRF Strep-Tactin®-Tb cryptate HTRF®

HTRF Strep-Tactin®-Tb cryptate can be used to capture Strep-tag® II and Twin Strep-tag®-tagged proteins.

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  • No-wash No-wash
  • Ease-of-use Ease-of-use
  • High affinity High affinity

HTRF Strep-Tactin®-Tb cryptate can be used to capture Strep-tag® II and Twin Strep-tag®-tagged proteins.



Strep-Tactin® has been labeled with Tb crypate. Biotin, Twin Strep-tag® and Strep-tag®II bind to Strep-Tactin® with high affinity. The binding is rapid and stable, making it an ideal choice for use in a variety of assays such as enzyme assays, protein-protein binding assays, and molecular biology assays.



Assay principle

In an HTRF interaction assay, one partner is labeled (directly or indirectly) with the donor, and the other with the acceptor (again, directly or indirectly). The intensity of the signal is proportional to the binding of the 2 partners. In the example shown here, Strep-Tactin®-Tb binds to the Strep-Tag®II tagged partner A, while partner B* binds to a specific Ab labeled with an HTRF acceptor.

*partner B can also be biotinylated, tagged, Fc fused. In these cases, use the corresponding HTRF reagent (anti-Tag, anti-species, protA, Streptavidin) labeled with an acceptor for the detection.

Principle of the HTRF protein-protein interaction assay Strep-tactin Tb cryptate

Assay protocol

The example on the right describes the protocol using a 20 µL final assay volume for detection of an interaction between a Strep-Tag®II-tagged partner A and a non-tagged partner B*. Dispense the 2 partners (10 µL), incubate, add Strep-Tactin®-Tb cryptate (5 µL) and anti-partner B labeled with acceptor (5 µL), incubate, and then read.

*partner B can also be tagged, Fc fused or directly labeled. In these cases, use the corresponding HTRF reagent (anti-Tag, anti-species, protA, Streptavidin), labeled with an acceptor for the detection.

Protocol of the HTRF protein-protein interaction assay Strep-tactin Tb Cryptate

How do the number of tests relate to the active moiety?

The average conjugate quantity per well reflects the overall biological material content. Using the active moiety amount is generally preferred to the quantity of total conjugate. For Cryptate and d2 conjugates, the total conjugate amount equals that of the active moiety, since the molecular weight of the label is negligible. This is not the case for XL665 labeled entities, for which the total quantity of conjugate will vary depending on the final molar ratio of the XL665 conjugate. However, the amount of active moiety indicated by Cisbio is constant and based on the number of tests ordered.

Active Moiety

Recommended quantities of Cryptate and XL665 conjugates

Cryptate conjugates must not be excessive, in order to prevent reader saturation and an unacceptable level of background. In most cases, a cryptate concentration of 1 to 5nM is appropriate, and will generate 20,000 to 80,000 cps at 620 nm depending on the HTRF compatible reader used. The XL665 conjugate must match its assay counterpart as closely as possible in order for the maximum number of biomolecules to be tagged with the XL665 acceptor. Thus, to detect a tagged molecule at an assay concentration of 20nM, the concentration of anti-Tag-XL665 should be equimolar or higher.

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Product Insert Strep-Tactin-Tb / 610STTLA-610STTLB

610STTLA-610STTLB - Product Insert

Batch Information Strep-Tactin-Tb / 20250831

610STTLA Batch 01A - Batch Information

Batch Information Strep-Tactin-Tb / 20250831

610STTLB Batch 01A - Batch Information

Plate Reader Requirement

Choosing the right microplate reader ensures you’ll get an optimal readout. Discover our high performance reader, or verify if your lab equipment is going to be compatible with this detection technology.

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