The adsorption of proteins at interfaces plays a role in many fields, such as health, food, environment and analysis. Fundamental aspects are useful when considering applications. We focus here especially on solid-liquid interfaces and present a few fundamental studies regarding adsorption kinetics and conformational changes, and examples of applications to sensors and membranes.
The first part is dedicated to fundamental studies performed using optical waveguide lightmode spectroscopy, as an example of a technique that has the advantage of not requiring labelled proteins, but is limited to specific supports. Conversely, the radiolabelling of proteins, which has the disadvantage of any labelling process, allows application to any kind of surfaces. As proteins bear both positive and negative charges, we can expect the influence of an electric field normal to the interface on the packaging order at interfaces. The refining of data treatment may also lead to the determination of useful structural parameters. The balance between protein-surface and protein-protein interactions is a key point for the description of the structure at high coverage of the surface. Electrokinetic methods, like measurement of the streaming potential, may be helpful in the electrical characterisation of the interfacial layer facing the solution.
The second part includes different bench techniques that were developed to improve the sensitivity of the characterisation of the orientation and structure of the proteins at interfaces: dual polarisation interferometry and total internal reflection ellipsometry are such recent examples. Concerning the determination of the secondary structure at interfaces, Fourier transform infrared (FTIR) spectroscopy and circular dichroism are very well adapted. Application to flat model surfaces can be performed by using the attenuated total reflectance-FTIR technique. The accessibility to the internal part of globular proteins is measured by the hydrogen-deuterium exchange rate. The evaluation of proteins on biodevices by time of flight - secondary ion mass spectroscopy is certainly a challenge given the size of the molecules. Data treatment according to mutual information theory, however, might be very helpful.
The third part considers studies more closely linked to applications. Determination of the conformation and orientation of the proteins at in terfaces is of particular importance for the understanding of the behaviour of cells at interfaces. A model study is presented with fibronectin at polymer surfaces with graded characteristics such as hydrophilicity, charge density and swelling. In addition to sensors, materials with a large area of contact with solutions containing proteins can be used in large-scale applications. Microporous membranes and textiles are typically representative of this category. They can act as concentrators of enzymes for the high-yield transformation of substrates. The biocompatibility of these materials, however, with the specific significance of anti-fouling properties and/or retaining enzyme activity, is a key parameter for satisfactory functioning. Different approaches for obtaining protein-resistant surfaces from poly-acrylonitrile membranes are presented. The modulation of the adsorption and activity of biomolecules can also be performed by surface modification of polypropylene membranes. One important "bio-inspired" route to surface modification is the introduction of phosphorylcholine moieties, since the zwitterionic group of the phospatidylcholine and sphingomyelin polar head covers a large fraction of the external surface of the erythrocyte and platelet membranes.
I would like to thank the authors for their contributions and the editorial staff of Springer for their assistance. I hope that this book may stimulate initiatives of work in the constantly renewing and fascinating field of interfacial phenomena.
Montpellier, February 2006 Philippe Déjardin
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