Equilibrium adsorption of LDL and gold immunoconjugates to affinity membranes containing PEG spacers

The objective of this study was to provide insight into the effects of spacer chemistry on immunoaffinity separations for the capture of large macromolecules and biological complexes. Immunoaffinity membranes were prepared by immobilization of immunoglobulin G (IgG) to flat sheet microporous membranes. Two different systems were examined: immobilized IgG for the immunoadsorption of human low-density lipoprotein (LDL) and immobilized IgG for the immunoadsorption of gold particle immunoconjugate. The IgG was immobilized either directly to the membrane or via a polyethylene glycol (PEG) spacer. Adsorption of LDL was significantly greater for anti-LDL IgG immobilized via PEG than for IgG immobilized directly to the membrane. With the PEG spacer, the adsorption capacity for LDL matched the theoretical density of a monolayer of LDL particles on the membrane surface. The gold particle immunoconjugate, similar in size to LDL, was examined as a generalized model of restrictions to immunoaffinity adsorption of large (>20 nm) biological complexes. Adsorption of gold particles was greater for IgG immobilized via PEG than for IgG immobilized directly to the membrane. It is postulated that the PEG spacer allows lateral movement of the immobilized IgG and dense monolayer packing of adsorbed particles on the membrane surface. These results are pertinent to the removal of LDL from human plasma and the purification of gene therapy delivery vectors, viral vaccines, and other large biological complexes.