Supported lipopolymer membranes as nanoscale filters: Simultaneous protein recognition and size-selection assays

A technique for size-selective discrimination of protein analytes was developed by incorporating poly(ethylene glycol) (PEG) lipopolymers into supported lipid bilayers. The membranes also contained biotinylated lipids, which recognized both streptavidin and anti-biotin IgG. By employing various PEG lipopolymer concentrations, clear discrimination against anti-biotin (M_w = 150000 Da) binding could be observed, which became more pronounced at higher polymer densities. On the other hand, streptavidin (M_w = 52800) binding to the membrane remained unaffected even at PEG concentrations that were well into the mushroom-to-brush phase transition. These observations were exploited to create an on-chip ligand-receptor binding assay that favored streptavidin binding over anti-biotin by several orders of magnitude in the presence of the lipopolymer. Control experiments revealed that the two proteins are bound to similar extents from a multi-protein analyte solution in the absence of PEG.