  Nanofilms of thickness of about two nanometers have been formed at the
air-water interface using functionalized castor oil (ICO) with cross-linkable
silylated groups. These hybrid films represent excellent candidates for
replacing conventional polymeric materials in biomedical applications, but they
need to be optimized in terms of biocompatibility which is highly related to
protein adsorption. Neutron reflectivity has been used to study the adsorption
of two model proteins, bovine serum albumin and lysozyme, at the silylated oil
(ICO)-water interface in the absence and presence of salt at physiologic ionic
strength and pH and at different protein concentrations. These measurements are
compared to adsorption at the air-water interface. While salt enhances
adsorption by a similar degree at the air-water and the oil-water interface,
the impact of the oil film is significant, with adsorption at the oil-water
interface three-to four-fold higher compared to the air-water interface. Under
these conditions, the concentration profiles of the adsorbed layers for both
proteins indicate multilayer adsorption: The thickness of the outer layer
(oil-side) is close to the dimension of the minor axis of the protein molecule,
~ 30 {\AA}, suggesting a side-way orientation with the long axis parallel to
the interface. The inner layer extends to 55-60 {\AA}. Interestingly, in all
cases, the composition of oil film remains intact without significant protein
penetration into the film. The optimal adsorption on these nanofilms, 1.7-2.0
mg$\bullet$m-2 , is comparable to the results obtained recently on thick solid
cross-linked films using quartz crystal microbalance and atomic force
microscopy, showing in particular that adsorption at these ICO film interfaces
under standard physiological conditions is non-specific. These results furnish
useful information towards the elaboration of vegetable oil-based nanofilms, in
direct nanoscale applications or as precursor films in the fabrication of
thicker macroscopic films for biomedical applications. 2
