Preparation of a dipalmitoylphosphatidylcholine/cholesterol Langmuir-Blodgett monolayer that suppresses protein adsorption

The adsorption patterns of human serum albumin (HSA) on the monolayers of d ipalmitoylphosphatidylcholine (DPPC) and DPPC/cholesterol mixtures were stu died by using the tapping mode atomic force microscopy (AFM). The pure DPPC and DPPC/cholesterol monolayers with different packing density were deposi ted on alkylated substrates by using the Langmuir-Blodgett technique, with the varying concentrations of cholesterol. The structures of solid supporte d pure DPPC and solid supported DPPC/cholesterol monolayers were analyzed b y using AFM, ellipsometry, and cyclic voltammetry. The results indicated th at the 10-30 mol % cholesterol mixed monolayers had densely packed and orde red structures, but the 50 mol % cholesterol mixed monolayer had irregular and disordered structures. When the DPPC and DPPC/cholesterol monolayers we re exposed to a 0.1 mg/mL solution of HSA, the adsorption patterns of album in indicated that the pure DPPC and the 50 mol % cholesterol mixed monolaye rs greatly activated protein adsorption, whereas the 10-30 mol % cholestero l mixed monolayers strongly suppressed protein adsorption due to highly pac ked phosphocholine groups. Highly packed DPPC molecules in the monolayer we re vertically oriented and the protein-resistant neutral phosphocholine gro ups were in direct contact with proteins, thereby reducing protein adsorpti on. Therefore, the protein adsorption patterns greatly depended on the cond ensing effect of cholesterol in the DPPC monolayer.