Adsorbed Layers of Ferritin at Solid and Fluid Interfaces Studied by Atomic Force Microscopy

doi:10.1006/jcis.1999.6680

Journal of Colloid and Interface Science

Volume 223, Issue 2, 15 March 2000, Pages 261-272

https://doi.org/10.1006/jcis.1999.6680 Get rights and content

Abstract

The adsorption of the iron storage protein ferritin was studied by liquid tapping mode atomic force microscopy in order to obtain molecular resolution in the adsorbed layer within the aqueous environment in which the adsorption was carried out. The surface coverage and the structure of the adsorbed layer were investigated as functions of ionic strength and pH on two different charged surfaces, namely chemically modified glass slides and mixed surfactant films at the air–water interface, which were transferred to graphite substrates after adsorption. Surface coverage trends with both ionic strength and pH indicate the dominance of electrostatic effects, with the balance shifting between intermolecular repulsion and protein–surface attraction. The resulting behavior is more complex than that seen for larger colloidal particles, which appear to follow a modified random sequential adsorption model monotonically. The structure of the adsorbed layers at the solid surfaces is random, but some indication of long-range order is apparent at fluid interfaces, presumably due to the higher protein mobility at the fluid interface.

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It should be mentioned that similar trends as these shown in Fig. 8 were also observed for other proteins. For example Johnson et al. [97] showed using the direct AFM imaging under wet conditions that the maximum surface coverage of ferritin on modified glass systematically increase with the ionic strength (the κdH parameter). For low κdH range it was ca. 0.2, and for κdH = 14 it attained 0.53, i.e., the value close to hard particle monolayers.
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²: Present address: Westvaco Corp., P.O. Box 118005, Charleston, SC 29423.

¹: To whom correspondence should be addressed. Fax: +1-302-831-4446. E-mail: [email protected].

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Regular ArticleAdsorbed Layers of Ferritin at Solid and Fluid Interfaces Studied by Atomic Force Microscopy

Abstract

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Adsorbed Layers of Ferritin at Solid and Fluid Interfaces Studied by Atomic Force Microscopy