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 spac er chemistry on immunoaffinity separations for the capture of large macromo lecules and biological complexes. Immunoaffinity membranes were prepared by immobilization of immunoglobulin G (IgG) to flat sheet microporous membran es. Two different systems were examined: immobilized IgG for the immunoadso rption of human low-density lipoprotein (LDL) and immobilized IgG for the i mmunoadsorption of gold particle immunoconjugate. The IgG was immobilized e ither directly to the membrane or via a polyethylene glycol (PEG) spacer. A dsorption 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 mono layer of LDL particles on the membrane surface. The gold particle immunocon jugate, similar in size to LDL, was examined as a generalized model of rest rictions to immunoaffinity adsorption of large (>20 nm) biological complexe s. Adsorption of gold particles was greater for IgG immobilized via PEG tha n for IgG immobilized directly to the membrane. It is postulated that the P EG spacer allows lateral movement of the immobilized IgG and dense monolaye r packing of adsorbed particles on the membrane surface. These results are pertinent to the removal of LDL from human plasma and the purification of g ene therapy delivery vectors, viral vaccines, and other large biological co mplexes. (C) 1999 Elsevier Science Ltd. All rights reserved.