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Detection of fibrinogen monolayers on mica by the colloid enhancement

Nattich-Rak M., Adamczyk Z., Wasilewska M., Radziszewska M.

Environmental Biotechnology

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2011

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Vol. 7, No. 1

1-11

EN

Physicochemical properties of bovine plasma fibrinogen (Fb) in electrolyte solutions were characterised, comprising the diffusion coefficient (hydrodynamic radius), electrophoretic mobility (zeta potential) and the isoelectric point, found to be at pH=5.8. Similar electrokinetic measurements were performed for the mica substrate using the streaming potential cell. The kinetics of Fb adsorption on mica under diffusion-controlled transport was also studied. The surface concentration of Fb on mica was determined directly by AFM counting. By adjusting the time of adsorption, and bulk Fb concentration, monolayers of desired coverage were produced. It was confirmed that Fb adsorbed irreversibly on mica both at pH=3.5 and pH=7.4 (physiological value). It was postulated that in the latter case, where both the substrate and fibrinogen molecules were negatively charged, adsorption was due to heterogeneous charge distribution over the protein molecule. In order to check this hypothesis, monolayers of Fb on mica were studied using the colloid enhancement (CE) method, in which negatively and positively charged latex particles were used. Results of these experiments were quantitatively interpreted in terms of the fluctuation theory assuming that adsorption sites consisted of two and three Fb molecules, for pH=3.5 and 7.4, respectively. This allowed one to determine limits of applicability of the classical DLVO theory and confirm a heterogeneous charge distribution over the Fb molecule. It was also concluded that the CE method can be used for a sensitive determination of the Fb bulk concentration for the range inaccessible for other methods, i.e., for 0.1ppm and below. Another effect of vital significance confirmed in this work was that for some range of fibrinogen coverage both the negative and positive latexes efficiently adsorbed. This indicates the formation of superadsorbing surfaces having potential significance for various filtration processes.

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Kinetics of random sequential adsorption of interacting particles on partially covered surfaces

Weroński P.

Bulletin of the Polish Academy of Sciences. Chemistry

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2003

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Vol. 51, No. 3-4

221-239

EN

The random sequential adsorption (RSA) approach was used to analyse adsorption kinetics of charged spheres at charged surfaces precovered with smaller sized, likely charged particles. The algorithm of M. R. Oberholzer et al. [20] was exploited to simulate adsorption allowing electrostatic interaction in three dimensions, that is, particle-particle and particle-surface interactions during the approach of a particle to the substrate. The calculation of interaction energies in the model was achieved with the aid of a many-body superposition approximation. The effective hard particle approximation was used for determination of corresponding simpler systems of particles, namely: the system of hard spheres, the system of particles with perfect sink model of particle-interface interaction, and the system of hard discs at equilibrium. Numerical simulations were performed to determine adsorption kinetics of larger particles for various surface concentration of smaller particles. It was found that in the limit of low surface coverage the numerical results were in a reasonable agreement with the formula stemming from the scaled particle theory with the modifications for the sphere-sphere geometry and electrostatic interaction. The results indicate that large particle-substrate attractive interaction significantly reduces the kinetic barrier to the large, charged particle adsorption at a surface precovered with small, likely charged particles.

3

Colloid adsorption at heterogeneous surfaces

Adamczyk Z., Siwek B., Jachimska B., Kowal A.

Bulletin of the Polish Academy of Sciences. Chemistry

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2002

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Vol. 50, No. 3

347-357

EN

Irreversible adsorption of colloid particles at heterogeneous surfaces was studied experimentally. The substrate of controlled heterogeneity was produced by covering mica sheets by colloid iron oxide (hematite) particles to a desired concentration. The particles of averaged diameter of 70 nm were produced by forced hydrolysis of FeCls solutions followed by a hydrothermal ageing. The coverage of colloid hematite particles (heterogeneity degree) was determined by electron microscopy and atomic force microscopy (AFM). Adsorption kinetics of polystyrene latex (averaged diameter 0.87Mim) at heterogeneous surfaces was studied by using the direct optical microscope observations in the impinging-jet cell. It was demonstrated that the initial adsorption rate attained the limiting value pertinent to homogeneous surfaces for heterogeneity degree of a few per cent. This behaviour was quantitatively interpreted in terms of the theoretical model considering the coupling between surface and bulk transport of particles. Similarly, the experimental results obtained for higher surface coverage of latex (long adsorption times) were in a good agreement with the random sequential adsorption (RSA) model.