Optical properties of proteins and protein adsorption study

Haemocompatibility is one of the most important properties, together with the tissue compatibility, corrosion and wear resistance that determine the biocompatibility of the artificial implants. Carbon-based thin films, such as amorphous carbon and amorphous hydrogenated diamond-like carbon (a-C:H or DLC) are considered as excellent candidates in order to be used as biocompatible coatings on biomedical implants. The aim of this work is to develop a methodology in order to study the protein adsorption phenomenon on thin films and to explore the optical properties of two basic blood plasma proteins, human serum albumin (HSA) and fibrinogen (Fib) and their adsorption mechanisms on amorphous hydrogenated carbon (a-C:H) thin films. Two techniques advantageous for the study of biological samples are used: Vis–UV spectroscopic ellipsometry (SE) and atomic force microscopy (AFM).a-C:H Films are grown with rf reactive magnetron sputtering. Static and real-time SE measurements are made. In the energy range of Vis–UV, proteins are almost transparent, while they present an absorption peak at higher energies. Different protein adsorption behaviour is observed on amorphous hydrogenated carbon films deposited under different conditions. This is probably due to their different surface structure, composition and topography of the surface and its interaction with the protein molecule. Adsorption phenomenon is studied through AFM technique as well. AFM results are in accordance with those derived by SE. The combination of the two techniques provides us a more accurate description of protein adsorption mechanisms.