Monomolecular films of cholesterol oxidase and S-Layer proteins

► Reproducible and stable Langmuir films of cholesterol oxidase were obtained. ► S-Layer proteins extracted from Bacillus sphaericus were used to produce monolayers. ► S-Layer protein monolayers were also reproducible and very stable. ► No hysteresis was observed until a surface pressure of 15 mN m−1. ► Mixed films exhibiting an ideal-like behavior were obtained.