A NEUTRON REFLECTIVITY STUDY OF POLYMER-MODIFIED PHOSPHOLIPID MONOLAYERS AT THE SOLID-SOLUTION INTERFACE - POLYETHYLENE GLYCOL-LIPIDS ON SILANE-MODIFIED SUBSTRATES

The structure of polymer-decorated phospholipid monolayers at the soli d-solution interface was investigated using neutron reflectometry. The monolayers were composed of distearoylphosphatidylethanolamine (DSPE) matrixed with varying amounts of DSPE-PEG (DSPE with polyethylene gly col covalently grafted to its headgroup). Mixed lipid monolayers were Langmuir-Blodgett deposited onto hydrophobic quartz or silicon substra tes, previously hydrophobized by chemically grafting a robust monolaye r of octadecyltrichlorosilane (OTS). We show that this method results in homogeneous and continuous phospholipid monolayers on the silanated substrates and determine that the grafted PEG chains extend away from the monolayers into the solvent phase as a function of their density, as expected from scaling theories. In addition, ligands were coupled to the end of the PEG chains and selective binding was demonstrated us ing fluorescence microscopy. Our results demonstrate that these constr ucts are ideal for further characterization and studies with well-defi ned monomolecular films.