Products | SPR Sensor chips | Data sheets

Strep-Tactin XT–modified sensor chips (ST)

XanTec’s Strep-Tactin XT–modified (ST) sensor chips are coated with a bioinert (poly)carboxylate matrix pre-functionalized with a recombinant 52 kDa Strep-Tactin XT tetramer. Although a member of the avidin family, Strep-Tactin XT exhibits only weak micromolar affinity for biotin and is therefore not suitable for stable immobilization of biotinylated biomolecules. Instead, it binds the 3 kDa Twin-Strep-Tag (TST) sequence with exceptionally high picomolar affinity, displaying typical dissociation rates (koff) of ≤ 10−5 s−11,2.

This enables defined, site-directed immobilization of TST fusion proteins under physiological conditions, ensuring uniform ligand orientation and preservation of biological activity. The Strep-Tactin XT/TST complex can be quantitatively regenerated using brief pulses of 3 M guanidine·HCl, with ST chips tolerating more than 100 regeneration cycles.

Compared with NTA/His-tag systems, ST chips exhibit markedly lower nonspecific binding of proteins and peptides, making them particularly suitable for kinetic and affinity studies involving these analytes.

XanTec offers three versions of Strep-Tactin XT–modified chips. The 2D STP chip provides superior diffusion properties, ideal for bulky analytes or weak binders with rapid kinetics. The STD200L and STHC200M chips enable higher immobilization densities for applications involving smaller analytes.

Key features:

Schematic illustration of a 3D ST sensor chip. Red dots represent negatively charged carboxyl groups distributed along the green polymer chains. The magnified view depicts an immobilized Strep-Tactin XT tetramer (turquoise) capturing a protein ligand (yellow) via a Twin-Strep-Tag (blue).3
Product code STP STD200L STHC200M
Base coating 2D, ultra-short CM-dextran (high density) 3D, 200 nm bioinert CM-dextran (low density) 3D, 200 nm bioinert polycarboxylate (medium density)
Capture immobilization capacity [µRIU]4 ≈ 500–1,000 ≈ 5,000–7,000 ≈ 5,000–7,000
Recommended ligands TST-modified proteins and peptides
Recommended analytes
  • proteins
  • peptides
  • nucleic acids
  • viruses and cells
  • proteins
  • peptides
  • nucleic acids
  • small molecules
  • proteins
  • peptides
  • nucleic acids
  • small molecules
  • carbohydrates
Intended purpose
  • reversible capture of TST-modified ligands
  • kinetics of medium and large analytes
  • especially suitable for weak binders with fast on- and off-rates
  • reversible capture of TST-modified ligands
  • kinetics of medium and small analytes
  • applications requiring high capture densities
  • reversible capture of TST-modified ligands
  • kinetics of medium and small analytes including carbohydrates
  • applications requiring high capture densities

1 Apparent dissociation rate constants (koff) determined at ligand capture densities < 50% of maximum immobilization level.

2 Binding of Strep-Tag II is feasible but exhibits limited stability (koff ≈ 10−2–10−3 s−1).

3 All illustrations are schematic representations and are not drawn to scale; dimensions, densities, and spatial relationships do not reflect actual physical or chemical proportions.

4 Based on specific capture immobilization of 500 nM TST-GFP in PBS.