Directional Sensing of Protein Adsorption on Titanium with a Light-Induced Periodic Structure
Directional dependence of adsorbed human plasma fibrinogen (HPF) and human serum albumin (HSA) on highly ordered pyrolytic graphite (HOPG), on polished titanium (Ti(p)), and on titanium with a light-induced periodic surface structure (Ti(LIPSS)) was investigated. Analyses, in the temporal domain, were conducted with a diffractive optical element (DOE)-based sensor that senses both topography (optical roughness) and reflectance related (gloss) parameters of the biomolecule-covered surface in phosphate buffered saline. Optical analysis was conducted from data measured with DOE in vitro. During the measurements, the probing laser beam had three different angular directions of the electric field of photons to inspect the directional responses from the studied surface types. First, results showed that the HOPG was found to be statistically inert for the measured biomolecule HPF adsorption, but with HSA, it was found to be adsorbed onto the HOPG surface. The Ti(p) and Ti(LIPSS) showed a more reactive adsorption process in comparison to the HOPG. Second, the directional dependence from the electric field angle of the probe beam had a clear effect only with the measured Ti(LIPSS) surface, which was produced for this investigation. Third, the existence of trapped gas nanobubbles was observed on the HOPG and on the Ti(p) sample surfaces with the HPF molecule. Fourth, the HPF and the HSA molecules showed different DOE responses on all studied surfaces, which was interpreted to be caused by the structural differences of these two proteins. Finally, ellipsometric measurements were performed to confirm the analysis of the DOE gloss signals.