Salt-induced immobilization of affinity ligands onto epoxide-activated supports

The immobilization of affinity ligands onto epoxy-activated stationary phases is enhanced at high concentrations of certain salts, such as ammonium sulfate and potassium phosphate. This enhancement is thought to occur because of a salt-induced hydrophobic interaction between the affinity ligand and the surface of the stationary phase. The increase in concentration of the affinity ligand near the reactive epoxy groups leads to an increase in the rate of reaction between the nucleophilic groups on the affinity ligand and the epoxide. The salt-induced enhancement is applicable to proteins and nucleotides at neutral pH and to small affinity ligands at elevated pH. In most cases, the hydrolysis of the epoxy groups does not limit the amount of affinity ligand immobilized. This review discusses the use of high salt concentrations to immobilize proteins, oligonucleotides and peptides to epoxy-activated silica and polymer supports. These modified supports can be used in affinity applications such as affinity chromatography or immunoassays.