In situ characterization of the adsorbed Concanavalin A on germanium surface at various pH

The adsorption of Concanavalin A (Con A) through pH cycle (pH 4.8-7.4-4.8) on germanium substrate was studied in situ by attenuated total reflection infrared (ATR-IR) spectroscopy. The qualitative and quantitative evaluation of the adsorbed protein layers was performed by the comparison of experimental spectra with simulated spectra of hypothetical surface layers using assumed parameters, such as composition, thickness, and structure of adsorbed layers. The results show that Con A readily adsorbs from phosphate-buffered saline, forming close to monolayer coverage on the surface of germanium covered with native oxide after short-time contact. Further adsorption was found to be pH dependent, and it is irreversible to pH changes. It was identified that the adsorption process is not solely electrostatically controlled. Protein-protein interaction by hydrogen bonding or hydrophobic interaction may dominate the adsorption process. The hydration of absorbed Con A layer at different pH was evaluated. The washing experiments with water and various electrolyte solutions confirmed physisorption of Con A on germanium surface. The experimental methodology using spectral simulation was proven to provide a deeper insight into the structure, composition, and hydration level of the produced protein coatings.