Ellipsometry as a tool to study the adsorption behavior of synthetic and biopolymers at the air–water interface

TLDR

The study investigates the use of ellipsometry to probe the adsorption behavior of proteins and synthetic macromolecules at the air–water interface. Ellipsometric measurements of surface density (Γ) and thickness were performed on κ‑casein, bovine serum albumin, and polyvinyl alcohol, and the results were validated against two independent techniques. Ellipsometry demonstrates that protein adsorption yields a constant refractive‑index increment, BSA reaches a plateau surface density of 2.9 mg m⁻² above 0.05 wt %, κ‑casein forms multilayers with increasing surface density, and the method provides insights into conformational changes, adsorption rates, and the conditions under which they occur.

Abstract

Abstract The application of ellipsometry of the study of the adsorption behavior of proteins and synthetic macromolecules at the air‐water interface has been investigated. It is shown that for macromolecules the amount adsorbed per unit area, Γ, as determined by ellipsometry, only has a well‐defined physical meaning if the refractive‐index increment remains constant up to high concentrations present in the adsorbed layer. It has been found experimentally that this conditioned is fulfilled for proteins. The ellipsometric Γ values of some protein agree satisfactorily with those obtained by two independent techniques has been used to investigate the adsorption from solution of κ‐casein, bovine serum albumin, and polyvinyl alcohol. For bovine serum albumin, Γ reaches a plateau value of 2.9 mg/m 2 for concentrations ≥ 0.05 wt%. The thickness of the adsorbed molecules. For κ‐casein, Γ steadily increases with increasing centration and multilayers are formed. The technique provides interesting information on conformational changes in adsorbed macromolecules, on the rate of the process, and on the conditions under which these occur.