Thin films. A biological example

There are many applications of ellipsometry in the measurement of mono-layer and sub-monolayer films. The theory of the optical signal to be expected from an adsorbed layer less than one monolayer thick has been placed on a firm footing by Smith [15] in some elegant experiments on adsorption in a Langmuir trough. Simultaneous ellipsometric and surface potential measurements were made on various molecules spread in thin layers on mercury as the surface pressure was varied. One conclusion was the simple result that the effective thickness divided by the thickness of the island molecules in the adsorbed islands was equal to the fractional coverage of the surface area. 

Two examples follow of the kind of information that ellipsometry can give about the adsorption of biological molecules. Ma et al. [18] studied the 

These ideas are being taken further in recent papers by Jonsson et al. [19] where the reactions between adsorbed and solution species are of the more specific antigen-antibody kind. Great attention is paid in this work to pretreating the silicon dioxide substrate to ensure that the active adsorbate is not denatured or changed in conformation. 

Ellipsometry was used in situ at all stages of the preparation of the substrates with their intermediate coatings as a monitor of surface concentration, and this study provides an excellent illustration of the power of the technique as a non-destructive and highly sensitive surface probe. 

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