An in situ study of protein adsorption on combinatorial Cu-Al films using spectroscopic ellipsometry

An approach to quantifying adsorbed protein layers at the protein/metal interface through spectroscopic ellipsometry using an in situ technique is described. A combinatorial binary Cu_1-xAl_x (0≤x≤1) linear composition gradient was prepared by magnetron sputter deposition. Studies on composition spread libraries of samples allow the screening of multiple compositions at once, resulting in less measurement time, less preparation time, better systematic experiments, increased reliability of data, and the opportunity for better understanding of the impact of composition on protein adsorption. Using a custom-designed tubular flow cell, the metallic thin films were exposed to protein solutions of fibrinogen and albumin at two concentrations. The thickness of adsorbed protein layers was monitored dynamically by spectroscopic ellipsometry. It was found that both fibrinogen and albumin preferentially adsorbed onto Cu-rich surfaces, and for an Al content above ∼21at.%, a significantly lower protein thickness was observed for both fibrinogen and albumin. These amounts depended greatly on the Al₂O₃ content of the film surface, with a higher oxide content leading to a decreased protein thickness. Vastly different amounts of fibrinogen were found to adsorb on pure copper when measured using in situ or ex situ techniques due to a copper corrosion effect that occurs during ex situ measurements.