Adsorption kinetics, ellipsometric study

Many ingenious methods have been introduced to study protein adsorption. If the kinetics of the adsorption process are important, the ellipsometric method introduced by Rothen (3) is probably the best. In this method protein adsorption can be studied ijn situ from a solution. The method has been used to study the kinetics of both the adsorption of protein in single layers and in double layers that can occur in the immune-reaction. When protein such as bovine serum albumin (BSA) was adsorbed from a dilute solution onto a surface, after a delay of a few seconds, steady-state diffusion controlled the adsorption process and, consequently, the amount bound to the surface increased linearly with time. However, as the surface became covered, adsorption slowed down, because it was now limited by the number of available sites on the surface. The final layer of BSA was roughly 2 nanometer thick. 

Although ellipsometry is well established as an experimental technique for the investigation of adsorbed layers, the number of studies at fluid/liquid interfaces is relatively small. Ellipsometry was used for investigation of the layer thickness between two immiscible liquids near the critical point (254, 255). This technique was also quite often used for in situ studies of the adsorption kinetics at an air/protein solution surface or polymer monolayers at an air/water interface (251, 256). It was also shown that ellipsometric re-... 

Fig. 3. Adsorption kinetics for human fibronectin on a hydrophobic silicon surface. The parameter Delta is obtained from ellipsometric studies and is a measure of the adsorbed amount of organic material on the surface. The triangles represent the result when the final protein concentration (30 pg/ml) was added at once. The circles represent subsequent additions to a final concentration of 30 pg/ml. The first addition was 2.5 pg/ml. (The dashed lines show the type of kinetics expected from the simple dynamic model presented here if steady state is achieved during the first addition.) The experimental points are taken from Jonsson et al. [8]...

A proper choice of the dipping time presupposes a study of the adsorption kinetics. In situ measurements of the adsorption of PAH (from a 0.01 M solution with 0.5 M MnCl2 added) on a PSS-coated optical waveguide showed that the adsorption is practically completed after 3 minutes [107]. It was shown that the kinetics of adsorption are not transport limited. Similar results hold for subsequent polyelectrolyte adsorption. Ellipsometric measurements of the thickness of... 

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