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Products | SPR Sensor chips | Hydrogels

Hydrogels

With a sufficiently sensitive detector, 2D surfaces are a good basis for many biomolecular interaction studies; however, numerous applications require a ligand density greater than one monolayer, either because the analyte is small (<2 kDa), or the optics are not sufficiently sensitive. In these cases, use of hydrogels can be advantageous.  A structurally flexible and strongly hydrated polymer brush is useful to shield the substrate and suppress non-specific interactions. Enhanced accessibility of the ligand’s binding sites and its increased mobility when immobilized through molecular spacers are further advantages of using hydrogels. Hydrogels can also help to solubilize hydrophobic ligands that would otherwise tend to form insoluble aggregates on the chip surface, and protect sensitive ligands against denaturation, especially in the dry state.

These advantages led to the development of surface-grafted, typically brush-structured, 3D hydrogels with thicknesses ranging from <10 nm to >1000 nm. These structures provide an increased density of attachment sites on the chip and, more importantly, use a higher volume fraction of the evanescent field for the specific interaction compared with 2D coatings. A welcome side effect of this approach is that the absolute influence of nonspecific factors such as bulk shifts decreases proportionally with increasing occupation of the evanescent field volume by the ligand–analyte pair.

In principle, surface-grafted hydrogels can be made from any water-soluble polymer; however, in practice, polycarboxylates, polyethers and polyols are preferred as they show significantly lower backgrounds than, for example, polyamines. In the early 1990s, the first commercial sensor chip coatings were derived from well-characterized, dextran-based solid phases for affinity chromatography. The most popular matrix material today is carboxymethylated dextran. Other carboxylated polysaccharides such as alginate, pectin, carboxymethylcellulose and hyaluronic acid can be used as well, but are less common. Because these polymers are of natural origin, their structures are often irregular; i.e., they can be more or less branched, or form hyperstructures such as helices or suprafibers. Furthermore, especially in the hydrated state, carbohydrates are relatively bulky molecules, occupying a considerable volume of the evanescent field that is then not available for the immobilization of ligand, and hindering the free diffusion of analyte.

For these and other reasons, efforts have been made to substitute polysaccharides with better defined synthetic polycarboxylates or zwitterionic polymers with lower background and smaller molecular footprints. In addition to reducing steric issues, coatings containing no hydroxyl groups have the advantage that they cannot form ester crosslinks upon EDC/NHS activation, a common side reaction occurring with carboxymethylated carbohydrates.

Hydrogel surfaces

3D immobilization matrices allow multilayer ligand immobilization which leads to significant signal amplification. They are employed for qualitative screening, concentration determinations and detection and kinetic analysis of low molecular weight compounds. As a rule of thumb, the smaller the analyte is, the thicker and denser the hydrogel structure should be.

The new hydrogel coatings of the HC family are currently available in four different thickness / porosity combinations: HC30M, HC200M, HC1000M and HC1500M. The HC type is based on a linear, synthetic polycarboxylate. Compared to the branched dextrans, it is better defined, shows a higher signal to noise ratio, has improved diffusion properties (better curve fits) and lower nonspecific interactions. Even more inert is the new HLC version which is available in the same thickness density combinations.

Hydrogel surfaces
Surface codeProduct description
AGAgarose hydrogel.
ALAlginate hydrogel.
AZD xAzide modified carboxymethyldextran surface. Click coupling.
50L, 200M
AZHC xAzide modified linear polycarboxylate hydrogel, medium charge density. Click coupling.
30M, 1500M
BDxBiotin, immobilized in a carboxymethyldextran hydrogel.
50L, 50M, 50D, 200L, 200M, 200D, 500L, 500M, 500D, 700L, 700M
BHC      Biotin, immobilized in a polycarboxylate hydrogel.
30M, 200M, 1000M, 1500M
C19RBDHC30M                                  Receptor Binding Domain (RBD) of SARS-CoV-2 Spike Protein immobilized on HC30M hydrogel
C xLinear polycarboxylate hydrogel, high charge density. Immobilization of nucleic acids.
30M, 80M, 150D
CMCCarboxymethylcellulose hydrogel.
CMD xxCarboxymethyldextran hydrogel.
50L, 50M, 50D, 200L, 200M, 200D, 500L, 500M, 500D, 700L, 700M
CMPG xCarboxymethylpolyethyleneglycol. Molecular weight: 4 kDa, alternative Mws upon request.
CS xxPolycarboxylate hydrogel, partially sulfonated. Preconcentration/immobilization of ligands with low pI.
30M, 80M, 150D
D xDextran hydrogel.
50M, 200M, 500M
DCD xDBCO modified carboxymethyldextran surface. Click coupling.

50L, 200M
GELGelatin hydrogel.
HC xPolycarboxylate hydrogel, medium charge density. Protein immobilization, standard.
30M, 200M, 1000M, 1500M
HEPHeparin. Approx. 50 nm hydrogel.
HLC Polycarboxylate hydrogel, low charge density. Extremely low level of non-specific interactions.
30M, 200M, 1000M, 1500M
HYHyaluronic acid hydrogel. Thin hydrogel with low non-specific interactions.
HZHC xHydrazide modified linear polycarboxylate hydrogel.
30M, 200M, 1000M, 1500M
LDLipophilic anchor groups attached to a 500 nm CM dextran hydrogel.
NAD xNeutravidin, immobilized in a carboxymethyldextran hydrogel. 

50L, 200M, 700L
NAHC xNeutravidin, immobilized in a linear polycarboxylate hydrogel. 

30M, 200M, 1500M
NIHC xPoly - NTA derivatized linear polycarboxylate hydrogel with high affinity.
30M, 200M, 1000M, 1500M
NID xxNTA derivatized carboxymethyldextran hydrogel.
50L, 50M, 50D, 200L, 200M, 200D, 500L, 500M, 500D, 700L, 700M
PAGDProtein A/G derivatized carboxymethyldextran hydrogel.
50L, 50M, 200L, 200M, 500L, 700L
PAGHCProtein A/G derivatized linear polycarboxylate hydrogel.
30M, 200M, 1000M
PCPectin hydrogel.
PEGPolyethyleneglycol. Molecular weight: 6 kDa, alternative MWs upon request.
PLYPoly-L-lysine.
SAHC xStreptavidin, immobilized in a linear polycarboxylate hydrogel.
30M, 200M, 1000M, 1500M
SAD xStreptavidin, immobilized in a carboxymethyldextran hydrogel.
50L, 50M, 50D, 200L, 200M, 200D, 500L, 500M, 700L, 700M
THC xDisulfide modified linear polycarboxylate hydrogel.
30M, 200M, 1000M, 1500M
TD xDisulfide modified carboxymethyldextran hydrogel.
50L, 50M, 50D, 200L, 200M, 200D, 500L, 500M, 500D
UVDUV crosslinker immobilized in a carboxymethyldextran hydrogel.
50L, 50M, 200L, 200M, 500L, 500M, 700L, 700M
ZCZwitterionic hydrogel. Cationic after NHS activation.
30M, 80M
ZCCCationic, zwitterionic hydrogel for pre-concentration scouting.
30M, 80M

The above mentioned SPR substrates are mainly intended for biomolecular interaction analysis, but may also be used as intermediate platforms for further modifications. The 2D and 3D coatings are covalently coupled to a protective interlayer and resist non-oxidative aqueous solutions from pH 1 - 13 as well as most organic solvents.

Alternative formats and custom coatings available upon request.