Products | SPR Sensor chips | Data sheets

  Instructions for use

  Related whitepaper: A superior alternative to His-Tag/NTA – Stable, reversible and highly specific immobilization on SPR sensor chips using Strep-Tactin®XT

Strep-Tactin XT–modified sensor chips

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, making it unsuitable for stable immobilization of biotinylated biomolecules. However, it possesses exceptionally high picomolar affinity for the small 3 kDa Twin-Strep-Tag (TST) sequence, with typical dissociation rates (koff) of ≤ 10⁻⁵ s⁻¹.1,2 This allows defined, site-directed immobilization of TST fusion proteins under physiological conditions, ensuring uniform ligand orientation and preserving 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 the NTA/His-tag system, ST chips display markedly lower nonspecific binding of proteins and peptides, making them ideal for kinetic and affinity studies involving these analytes. Together, these features establish ST sensor chips as an efficient and reliable tool for studying biomolecular interactions with TST fusion proteins, streamlining workflows and accelerating research.

XanTec offers three versions of Strep-Tactin XT–modified chips for SPR applications. The 2D STP chip provides superior diffusion properties, ideal for bulky analytes or weak binders with rapid kinetics, whereas the ST200L and STHC200M chips enable higher immobilization densities, well suited for 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 decaying red gradient represents the evanescent field. 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 TST-modified proteins and peptides 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 immobilization of TST-modified ligands
  • kinetics of medium and large analytes
  • especially suitable for weak binders with fast on- and off-rates
  • reversible capture immobilization of TST-modified ligands
  • kinetics of medium and small analytes
  • especially suitable for situations requiring high capture densities
  • reversible capture immobilization of TST-modified ligands
  • kinetics of medium and small analytes including carbohydrates
  • especially suitable for situations requiring high capture densities

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

2 Binding of Strep-Tag II is feasible but the complex exhibits limited stability, with dissociation rates of 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 the specific capture immobilization of 500 nM TST-GFP in PBS.