Albumin and fibrinogen adsorption onto phosphatidylcholine monolayers investigated by Fourier transform infrared spectroscopy

Dipalmitoylphosphatidylcholine (DPPC) monolayers were deposited onto a germanium attenuated total reflectance (ATR) crystal using the Langmuir-Blodgett technique. The DPPC-coated crystal was then exposed to human serum albumin or human fibrinogen solutions while measuring the protein adsorption by recording FTIR spectra. The effect of the zwitterionic nature of the DPPC polar headgroup towards protein adsorption has been ascertained by exposing either the phospholipid headgroup or the acyl chains to the protein solution; this was possible by the use of a silanized or a bare germanium crystal. Calibration curves have been made to measure the protein surface concentrations. After 3 h, the albumin surface concentration on DPPC monolayers was about three times higher when the proteins were exposed to the lipid acyl chains instead of the polar headgroups (e.g. 3 vs. 1 μg cm^-2). As for fibrinogen (FGN) adsorption, when the lipid polar headgroups were exposed to the protein solution, the FGN adsorption was low reaching a maximum value of 0.5 μg cm^-2. When interacting with the lipid acyl chains, the FGN adsorption reached a plateau at a value of 2.1 mg cm^-2 after 3 h. Clearly, both albumin and FGN showed a low tendency to adsorb on surfaces where the lipid polar headgroups are exposed toward the protein solution.