Fibronectin adsorption, conformation, and orientation on polystyrene substrates studied by radiolabeling, XPS, and ToF SIMS.

Protein adsorption is widely studied by a variety of techniques, but there still is little known about protein orientation and conformation after adsorption. This probably is due to the large number of parameters involved, such as the characteristics of the surface and the structure of the protein. In this study, the adsorption of fibronectin was investigated with three different techniques: radiolabeling, X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectrometry (ToF SIMS) on polystyrene and oxidized polystyrene. The first two techniques have been widely used to study protein adsorption, allowing us to determine the amount of protein adsorbed on each surface. The ToF SIMS, however, is a technique just emerging for the study of protein adsorption. This study confirms its utility since ToF SIMS is found to be sensitive to the protein orientation and/or conformation at the surface. Indeed, the ToF SIMS peaks characteristic of the protein show differences in their reduced intensity between the two substrates. These differences, which are not detected by XPS, are attributed to different orientations and/or conformations of the protein.