Molecular orientation distributions in adsorbed protein films

Abstract

Understanding and controlling protein adsorption is fundamentally important to the successful development of synthetic biomaterials and implantable chemical sensing devices. However, the study of protein adsorption, and in particular, orientation in protein thin films has been hampered by inadequate methods with which to study weakly absorbing thin protein films. In this work, Integrated Optical Waveguide-Attenuated Total Reflection Linear Dichroism (IOW-ATR LD) coupled with fluorescence emission anisotropy was used to study: (1) the orientation of Mb as a function of the adsorbent surface and surface coverage, and (2) the orientation distributions of cyt c adsorbed to various surfaces. It was found that the average molecular orientation of an adsorbed protein film: (1) is dependent on the chemical and/or physical characteristics of the adsorbent surface, and (2) is dependent on the protein surface coverage. It was also determined that the macroscopic order of an adsorbed protein film is dependent on the number of different types of protein-surface interactions in a given system. If there is one dominant type of interaction between the between the protein and the surface which is limited to a specific region on the surface of the protein, an ordered protein film will be produced. However, as the number of the type of protein-surface interactions increases, the distribution of orientations also increases, leading to a disordered film. Finally, a broadband waveguide coupling device has been developed which allows spectroscopic measurements of submonolayer to monolayer surface coverages of proteins to be performed.