| Product code | Prefix (designates the instrument): SCB, SCBS, SCBN, SPP, SCBI, SPSM, SCH, SPMX, SCR, SCS, SD + Add: STP, STHC200M, STD200L, Example: SCBS STHC200M |
|---|---|
| Intended purpose | Site-directed, reversible capture immobilization of Twin-Strep-tagged fusion proteins under physiological conditions with picomolar affinity. Recommended applications include the investigation of biomolecular kinetics involving proteins, peptides, nucleic acids and small molecules. |
| Storage | Store at -20 °C, desiccated over molecular sieve 4A or at 2–8 °C in physiological buffer. |
| Related products |
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STP, STD, and STHC sensor chips are coated with a bioinert polycarboxylate matrix, pre-functionalized with the 52 kDa Strep-Tactin®XT tetramer [1][2]. Though part of the avidin family, Strep-Tactin®XT has only a weak micromolar affinity for biotin, making it unsuitable for stable biotinylated biomolecule immobilization. However, it demonstrates exceptionally high picomolar affinity for the small 3 kDa Twin-Strep-Tag (TST) sequence, with typical dissociation rates (koff) of ≤ 10⁻⁵ s⁻¹ [3]. This allows precise, site-directed immobilization of TST-fusion proteins on XanTec ST sensor chips under physiological conditions, ensuring uniform ligand orientation and preserving activity.
The Strep-Tactin®XT/TST complex can be quantitatively regenerated with brief pulses of 3 M Guanidine·HCl, with ST sensor chips tolerating over 100 regeneration cycles. Compared to the NTA/His-tag system, ST chips offer significantly lower nonspecific binding in protein-rich environments, making them ideal for biomolecular interaction studies involving TST-fusion proteins and reducing assay optimization time. 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 provides three versions of Strep-Tactin®XT-modified sensor chips for SPR applications. The 2D STP chip offers superior diffusion properties, suitable for bulky analytes or weak binders with rapid kinetics, while the ST200L and STHC200M chips support higher immobilization densities, ideal for smaller analytes.
Twin-Strep-tagged biomolecule (to be provided by the user)
3 M Guanidine (product code B GU-50ML): 3 M Guanidine·HCl
Optional: Conditioning buffer 1 (product code B C1-50ML): 50 mM NaOH, 1 M NaCl
Ensure that the flow system of your SPR equipment is free from any protein contamination, as even small amounts of desorbed protein can accumulate on the charged sensor surface. If necessary, clean the system using either 1 % Tween 20 or, for a more stringent cleaning, 0.5 % SDS for 5 minutes, followed by 50 mM glycine·HCl (pH 9.5) for 10 minutes (both included in the Desorb Kit, product code K D-500ML). The glycine is required to remove residual traces of SDS.
Allow the sealed sensor chip pouch to equilibrate at room temperature to prevent condensation on the chip surface.
After opening the pouch, install the sensor chip by following the instrument manufacturer’s instructions.
Note: XanTec SPR sensor chips, like all nanocoatings, are prone to degradation when exposed to the atmosphere due to reactive oxygen species in the air. To prevent this, unmounted sensor chips should be stored in a closed container under an inert gas atmosphere or in a physiological buffer for short-term storage.
| Procedure | Flowrate [µL/min] |
Injection time [s] |
|
|---|---|---|---|
| 1 | Equilibrate your SPR-system with physiological running buffer like HBSTE or HBSTE+ and mount a compatible XanTec ST sensor chip. | ||
| 2 | Condition all channels with 3 M Guanidine·HCl. Wait until the baseline has stabilized. |
15 | 5x60 |
| 3 | Optional: Strip the surface with Conditioning buffer I. This step will decrease the binding capacity by 30 %–50 % but can improve the diffusion characteristics of the surface. | 15 | 600 |
| 4 | Divert your reference channel and inject your TST-fusion protein at concentrations of 2–50 nM. Low ligand concentrations and flow rates are recommended to achieve good control over ligand immobilization levels. Adjust conditions and repeat ligand injection as required to achieve the target immobilization level. Wait until the baseline has stabilized. |
1–10 | 60–300 |
| 5 | Start interaction analysis. | ||
| 6 | Regenerate the surface with 3 M Guanidine·HCl | 15 | 3x60 |
Avoid prolonged incubation of the sensor chip in water, as this can negatively affect the integrity of the sensor coating over time. Instead, use a physiological buffer like HBSTE.
For later reuse, sensor chips can be stored either dry or wet under physiological conditions. When handling the sensor chip, avoid touching the top coating with gloves or tweezers. Reuse of planar STP sensor chips is not recommended due to the lower overall stability and robustness of planar sensor coatings.
Biacore users only: To prevent detachment of the glass chip in the instrument after chips have been stored under buffer or at 100 % humidity, we strongly recommend checking the mechanical stability of the assembly before inserting the chip cartridge into the instrument.
Reichert users only: If the sensor chip is intended for later reuse, use the refractive index matching foil instead of immersion oil when installing the sensor chip for the first time. Oil traces may contaminate the hydrogel top coating after chip removal, potentially causing irreversible damage to the immobilized Strep-Tactin®XT.
| Dry storage | |
|---|---|
| 1 | Dismount the used sensor chip from your SPR instrument. |
| 2 | Rinse the hydrogel surface of the sensor chip carefully with ultrapure water. |
| 3 | Optional: Carefully remove excess water from the edge of the hydrogel coating using a pipette. Place a droplet (30 µL for SCB and SCBS) of XanTec stabilization buffer onto the wet chip surface and allow it to spread, ensuring it covers the entire surface. Let it dry for approximately 60 minutes in a desiccator with desiccant (4A molecular sieve). This step helps prevent denaturation of the immobilized Strep-Tactin®XT and prolongs the shelf-life of the sensor chip. |
| 4 | Dry the sensor chip with a jet of filtered air or nitrogen. |
| 5 | Store the sensor chip dry, using a 3A or 4A molecular sieve, in a cold environment (-25 °C) under an inert gas atmosphere in a tightly sealed container. The stability of the sensor chip depends on the stability of the immobilized ligand. The underlying hydrogel coating should remain stable for several weeks to months. |
| 6 | Reinstallation No protective top coating: Equilibrate the sensor chip to room temperature before opening the storage container, then insert the chip according to the instrument manufacturer‘s instructions. Protective top coating applied: Equilibrate the sensor chip to room temperature before opening the storage container. Immerse the chip in physiological buffer for 10 minutes to remove the protective layer from the hydrogel coating. Rinse gently with ultra-pure water and carefully dry it using a jet of filtered air or nitrogen. |
| Wet storage | |
|---|---|
| 1 | Dismount the used sensor chip from your SPR instrument. |
| 2 | Rinse the hydrogel surface of the sensor chip carefully with ultra-pure water. Place the sensor chip in a container filled with sterile filtered, physiological buffer and seal it tightly. For Cytiva sensor chips, 50 mL centrifugation tubes are applicable. Store the sensor chip refrigerated at 2–8 °C. The underlying hydrogel coating as well as the immobilized Strep-Tactin®XT should be stable for several days to weeks at such conditions. Long-term storage in water is not advised, as this can negatively affect the integrity of the sensor coating.. |
| 3 | Reinstallation Remove the sensor chip from the container, preferably using clean tweezers. Rinse with ultra-pure water to remove buffer salts, and carefully dry it using a jet of filtered air or nitrogen. Then, insert the chip according to the instrument manufacturer‘s instructions. |
| Issue | Possible solution |
|---|---|
| Inefficient regeneration | In cases where unsatisfactory regeneration is obtained, it might be worth trying 10 mM NaOH with 500 mM NaCl (freshly prepared) or 3 M MgCl2 as an alternative regeneration solution. Furthermore, the addition of 2 % dioxane or 0.1 %–0.25 % SDS to the regeneration solutions might be tested. However, acidic regeneration procedures should be avoided. |
| Instable baseline | Make sure that all solutions are free from biotin. This can be achieved by a desalting procedure, or by using a blocking agent such as avidin. Baseline drift can also be caused by very high immobilization levels. In this case, baseline stabilization after ligand immobilization must be extended. |
V. 11/24a
For in-vitro use only. Not for use in clinical diagnostic procedures.