Spatial Distribution of Proteins in the Adsorbed Layer

Neutron reflectrometry in combination with water-contrast variation can probe the interfacial layer thickness with a resolution of a few angstroms and has provided information on mean structural conformations for globular protein layers at the aqueous-solid interface (Follows et al. 2004; Lu et al. 2005; Marsh et al. 1999; Tiberg et al. 2001).

Direct imaging methods like atomic force microscopy (AFM), surface force microscopy (SFM) and scanning tunnelling microscopy are well suited for probing the protein morphology on solid supports (Haggerty and Lenhoff 1993a). Most studies of the adsorption of proteins by AFM have been carried out using dry-sample imaging methods (Ortega-Vinuesa et al. 1998). The number of in situ experiments on adsorption at the liquid-solid interface is much more limited (Kim et al. 2002). These techniques provide complementary information about parameters such as the lateral distribution of protein molecules on surfaces and also allow direct measurements of forces between the adsorbent phase and a single protein (Claesson et al. 1995). With SFM, measurements of forces and distances between two proteins coated on mica surfaces have been evaluated for bovine serum albumin (BSA; Perez and Proust 1987) and for lysozyme (Haggerty and Lenhoff 1993b). By tracking the effect of the chemical properties using self-assembled monolayers as chemically patterned surfaces, many AFM

studies track the effect of the chemical properties as well as the surface topology of the sorbent support on the conformation of the individual protein molecules in the adsorbed layer (Li et al. 2003; Marchin and Berrie 2003; Patel et al. 1998; Wadu-Mesthrige et al. 2000).

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