Kinetics of diffusion-controlled adsorption of colloid particles and proteins

A theoretical model was developed for describing localized adsorption kinet ics of proteins and colloid particles at solid/liquid interfaces. In contra st to previous approaches the adsorption and desorption rate constants as w ell as the surface blocking function were evaluated explicitly without usin g empirical parameters. It was also predicted that irreversible adsorption kinetics can unequivocally be characterized in terms of the adsorption rate constant I;, and the maximum (jamming) coverage Theta(mx) known for variou s particle shapes from previous Monte-Carlo simulations. The dimensionless constant (k) over bar(a) was shown to be inversely proportional to the conc entration of particles which is usually very low for protein and colloid ad sorption measurements. From the theoretical model it was also deduced that in this case the asymptotic adsorption law for large dimensionless time tau can be expressed as Theta(mx) - Theta similar to 1/tau(1/(n-1)) (where n = 3 for spheres, n = 4 for side-on adsorption of spheroids, n = 5 for random ly oriented spheroid adsorption). It was also shown that this limiting adso rption regime occurs for proteins at surface coverage Theta(1) very close t o the jamming value Theta(mx) becoming therefore difficult to detect due to limited experimental accuracy. These analytical predictions were found to be in agreement with numerical calculations performed by using the finite-d ifference scheme, valid for an arbitrary range of adsorption time. Moreover , it was demonstrated that these numerical results adequately reflected the experimental results of Johnson and Lenhoff who determined the kinetics of colloid particle adsorption using atomic force microscopy. Previously used approaches assuming that particle adsorption flux is reduced by the factor B(Theta) were found to be inadequate. It was also demonstrated that due to the similarity of underlying parameters the results obtained for colloid s ystems can be exploited as well-defined reference data for estimating the a dsorption kinetics Of proteins. (C) 2000 Academic Press.