Streptavidin & affinity reagents

Unique set of reagents for developing homogeneous high-throughput assays.

The streptavidin-biotin reaction is one of the most frequently used affinity systems. Streptavidin-biotin binding is rapid and relatively 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. Cisbio offers a line of HTRF Europium and Lumi4®-Terbium-Cryptate, XL665, and d2 conjugated streptavidins, to provide increased ease and flexibility in HTRF® assay development.

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Product Specifications

Build HTRF Protein-Protein interaction (PPI) assays for your specific application

Reagents are sold by the number of tests (384-well, 20 µl reactions). Antibodies conjugated to XL665 or d2 are supplied on the basis of 20ng of antibody per well. The amount of active moiety per vial is also provided (as well as the number of tracers per vial - see product description sheet). The active moiety is defined as the active part of a conjugate (e.g. antibody).

How do the number of tests relate to active moiety?

The average conjugate quantity per well is information that reflects overall biological material content. For Eu3+ cryptate and biotin conjugates, the total conjugate amount equals that of the active moiety, since the molecular weight of the label is negligible.

For XL665 labeled entities, however, the amount of active moiety will not equal the amount of total conjugate. In practice, using the active moiety amount is generally preferred to the quantity of total conjugate as a basis for calculating reagent usage per well during assay development. The quantity of total conjugate supplied by Cisbio Bioassays will vary depending on the final molar ratio of the XL665 conjugate. The amount of active moiety, however, is constant and based on the number of tests ordered.


Streptavidin is available labeled either with Europium or with Lumi4-Terbium Cryptate donors, and with XL665 or d2 acceptors. Cisbio Bioassays offers two XL-665 streptavidin conjugates: Streptavidin XL665 and Streptavidin-XLent!.

Streptavidin-XLent! is a high grade streptavidin-XL665 conjugate for which the coupling conditions have been optimized to yield a conjugate with enhanced performances for certain assays, particularly those requiring high sensitivity. When compared to competitor SA-APC conjugates, Streptavidin-XLent! shows overall superior performance (see figure below). Streptavidin-XLent! features include:

  • Improved signal-to-noise ratio
  • Higher performance
  • Increased sensitivity
  • Long term stability

Description Active Moiety/5,000 tests
Streptavidin K 9 µg
Streptavidin Tb 4 µg
Streptavidin XL665 250 µg
Streptavidin XLent! 250 µg
Streptavidin d2 250 µg
WGA XL665 100 µg

To compare Streptavidin-XLent! with other commercially available conjugates, HTRF reagents (Europium-Cryptate PT66 and Streptavidin-XLent!) and conjugates from two other suppliers were used in an HTRF tyrosine kinase assay.

Assay Performances

Streptavidin-XLent! produces an average signal increase of 40% for a variety of assays. Here, the figure shows the results of a side-by-side comparison of SA-XL665 and Streptavidin-XLent! for an EGFR tyrosine kinase assay. Over 25% less enzyme was required when using streptavidin-XLent! to produce identical assay signals. Not only does assay performance include increased sensitivity, but streptavidin-XLent! also means lower enzyme consumption - a key consideration when quantities of the enzyme are limited or cost prohibitive.

Increasing quantities of EGFR were incubated with biotinylated polyGAT (50 nM). The enzymatic reaction was stopped using EDTA following a 20 minute incubation. Europium-labeled PT66 (20 ng/well) and Streptavidin-XL665 (50 nM) or StreptavidinXLent! (50 nM) were added. HTRF signal was detected following a 20 minute incubation.

Part#, inserts & MSDS

Ordering Info

DescriptionCat. noProduct insertMSDS
Streptavidin-d2 - 5,000 tests610SADLA
Streptavidin-d2 - 20,000 tests610SADLB
Streptavidin-d2 - 1,000 tests610SADLF
Streptavidin-Eu cryptate - 5,000 tests610SAKLA
Streptavidin-Eu cryptate - 20,000 tests610SAKLB
Streptavidin-Tb cryptate - 5,000 tests610SATLA
Streptavidin-Tb cryptate - 20,000 tests610SATLB
Streptavidin-Tb cryptate - 1,000 tests610SATLF
Streptavidin-XL665 - 5,000 tests610SAXLA
Streptavidin-XL665 - 20,000 tests610SAXLB
Streptavidin-XL665 - 1,000 tests610SAXLF
Streptavidin-XLent! - 5,000 tests611SAXLA
Streptavidin-XLent! - 20,000 tests611SAXLB

Companion products

DescriptionCat. noProduct insertMSDS
PPI - Terbium detection buffer - 200 mL61DB10RDF
PPI - Europium detection buffer - 200 mL61DB9RDF