Bare gold SPR chips, non-functionalized gold coated plate
Carboxylate functionalized SPR chips carry negative charge in buffer with pH greater than 4. They covalently bind to primary amine groups after EDC/NHS activation. This binding is more efficient than aldehide-amine binging. Carboxyl groups are grafted to gold surface though selfassembled monolayer in planar chips. They are matrix free, so no diffusion problem. The mixed type of planar chips have short and long alkyl chains, and thus less steric hindrance when react with the shielded primary amines. Polyethylene glycol (PEG) is monofunctional polymer that is well known for resisting non-specific adsorption. Polysaccharides (dextran and arginic acid) have long and bulky chains that extend out from gold surface, and thus have increased reacting sites compared to planar surface. Synthetic polymers (SP) have long and slim chains. They take less space in the surface area than bulky polysaccharide chains do, and thus leave more space to the target molecules. SP type I is highly negatively charged polymer due to high density of carboxylate. SP type II is mildly negatively charged polymer. SP type III has long spacer arms that extend the carboxylate groups away from the main chains.
Amine functionalized SPR chips carry positive charge in buffer with pH less than 10. They covalently bind to biomolecules with EDC/NHS activated carboxyl groups.
Epoxide functionalized SPR chips covalently bind to thiol,amine, hydroxyl, and other nucleophilic groups. The reaction with hydroxyl groups requires high pH and takes more than 12 hours.
Maleimide functionalized SPR chips covalently bind to thiol groups (-SH). This reaction is very specific and fast.
Disulfide functionalized SPR chips covalently bind to thiol groups (-SH) through thio-disulfide exchange. After binding, the new formed disulfide bond can be broken by another thiol compound.
Ni complexed SPR chips bind to his-tagged proteins.
UV-initiator modified SPR chips covalently bind to all biomolecules under ultraviolet illumination. The reaction does not rely on any chemical groups on the biomolecules. It takes about 15 minutes under 100W UV lamp.
Protein A immobilized SPR chips bind to many mammalian immunoglobulins (antibodys), especially IgGs, through Fc region. It makes these chips good candidate for label free immunoassay
Streptavidin immobilized SPR chips bind to biotin-labeled biomolecules.