Products | SPR Sensor chips | Data sheets

NTA–modified sensor chips (Ni)

XanTec’s NiD and NiHC sensor chips are coated with a bioinert (poly)carboxylate hydrogel matrix modified with nitrilotriacetic acid (NTA) functionalities. These sensor chips enable the reversible capture immobilization of His-tagged biomolecules through complex formation with transition metal ions, preferably Ni2+. For sufficient binding stability, the His-tag should contain 6–10 histidine residues. Complete regeneration of both NiD and NiHC surfaces is typically achieved by removal of chelated Ni2+ ions using chelating agents (e.g., EDTA) or competitive ligands such as imidazole.

Binding characteristics:
NiD sensor chips exhibit predominantly monovalent interactions between NTA(Ni2+) complexes and His-tags, resulting in dissociation rates (koff) in the range of 10−3 s−1.
NiHC sensor chips support multivalent binding due to the flexibility of the polymer chains, increasing binding stability by up to three orders of magnitude. Baselines after His-tagged ligand capture show minimal to no drift, with typical koff values of 10−5–10−6 s−1.1

A known limitation of NTA-based capture surfaces is the potential for nonspecific interactions between chelated Ni2+ ions and protein analytes or complex sample matrices (e.g., FBS). Proteins containing exposed histidines or metal-affinity motifs may bind non-selectively, increasing background signals. For assays sensitive to nonspecific binding, alternative immobilization strategies (e.g., anti-His-tag antibody capture) should be considered.

Key features:

Schematic illustration of a 3D Ni sensor chip. Green and red dots represent NTA-bound Ni2+ ions and negatively charged carboxyl groups distributed along the green polymer chains. The decaying red gradient represents the evanescent field. The magnified view shows an NTA-bound Ni2+ ion coordinating a protein ligand (yellow) via its His-tag (light blue).2
Product code NiP NiD200M NiHC200M NiHC1500M
Base coating 2D, ultra-short bioinert CM-dextran
(high density)		 3D, 200 nm bioinert CM-dextran
(medium density)		 3D, 200 nm bioinert polycarboxylate
(medium density)		 3D, 1500 nm bioinert polycarboxylate
(medium density)
Capture immobilization capacity [µRIU]4 ≈ 120 ≈ 400 ≈ 1,200 ≈ 2,000
Ligands His-tagged peptides and proteins
Recommended analytes
  • proteins
  • large peptides
  • large nucleic acids
  • proteins
  • peptides
  • nucleic acids
  • nucleic acids
  • small molecules
  • peptides
  • carbohydrates
  • nucleic acids
  • small molecules
  • small carbohydrates
Intended purpose
  • suitable for weak binders
  • recommended in combination with EDC/NHS stabilization
  • equivalent to competitor NTA chips
  • suitable for weak binders
  • recommended in combination with EDC/NHS stabilization
  • ideal for medium to small analytes
  • higher capture densities
  • minimal baseline drift
  • maximum capture capacity
  • optimized for small analytes
  • minimal baseline drift

1 Maximum binding stability requires immobilization at approximately one-third of the chip’s maximum capture capacity.

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

3 Table includes a selection from XanTec’s full Ni sensor chip portfolio.

4 Binding capacities are based on the capture level of His6-peptide from a 5 µM solution after a 180 s stabilization period, with 1 µRIU corresponding approximately to 1 RU. Immobilization capacities of His-tagged proteins are considerably higher.