Water partial pressure X-ray photoelectron spectroscopy study of the conformation of fibrinogen on silanized hydrophilic/hydrophobic surfaces

Near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) allows the study of the conformational state of adsorbed proteins on surfaces at water partial pressures of a few mbar. In the present study, we used two organosilanes to prepare hydrophilic and hydrophobic surfaces. For the NAP-XPS study, human fibrinogen, a sorbent serum protein with conformational dependent function, was adsorbed on contrasting surfaces, studied at 2 mbar H 2 O vapor pressure and compared with analysis at ultrahigh vacuum (UHV). Two different excitation energies were used to gain in-depth sensitivity. The C 1s core level was fitted, and the components correlated with the presence of surface-exposed hydrophobic or hydrophilic moieties. The mode of analysis significantly affects the data on the conformation of fibrinogen on hydrophilic surfaces, showing surface-exposed (more intense) hydrophobic cues in the H 2 O NAP mode than in the UHV mode. Furthermore, the intensity of the C-H peak exhibits the greatest variability in intensity, being more surface segregated on hydrophilic surfaces than on hydrophobic ones. The latter statement is sustained only for H 2 O NAP conditions, with no significant differences observed in the UHV mode. The work envisages greater sensitivity for forthcoming analyses of adsorbed proteins and other biomolecules by using water partial pressure XPS mode.