The adsorption or adhesion of large particles (proteins, colloids, cells, . . . ) at the liquid-solid interface plays an important role in many diverse applications. Despite the apparent complexity of the process, two features are particularly important: 1) the adsorption is often irreversible on experimental time scales and 2) the adsorption rate is limited by geometric blockage from previously adsorbed particles. A coarse-grained description that encompasses these two properties is provided by sequential adsorption models whose simplest example is the random sequential adsorption (RSA) process. In this article, we review the theoretical formalism and tools that allow the systematic study of kinetic and structural aspects of these sequential adsorption models. We also show how the reference RSA model may be generalized to account for a variety of experimental features including particle anisotropy, polydispersity, bulk diffusive transport, gravitational effects, surface-induced conformational and orientational change, desorption, and multilayer formation. In all cases, the significant theoretical results are presented and their accuracy (compared to computer simulation) and applicability (compared to experiment) are discussed.

Most of the adsorption experiments of proteins on solid surfaces are interpreted with the Langmuir kinetic equation. We show that this equation does not accurately describe the surface exclusion effect. We propose improvements in twoJimiting cases; (i) the particles, once adsorbed, can diffuse rapidly on the surface; (ii) the particles can neither diffuse on the surface, nor desorb from it; the so called random sequential adsorption (RSA) model. In the last case, we compare our results with computer simulations.

We study the random sequential adsorption (RSA) of unoriented anisotropic objects onto a flat uniform surface, for various shapes (spherocylinders, ellipses, rectangles, and needles) and elongations. The asymptotic approach to the jamming limit is shown to follow the expected algebraic behavior, 0(03)-0(t)-t-1'3, where 8 is the surface coverage; this result is valid for all shapes and elongations, provided the objects have a nonzero proper area. In the limit of very small elongations, the long-time behavior consists of two successive critical regimes: The first is characterized by Feder's law, t-l", and the second by the t-1'3 law; the crossover occurs at a time that scales as E-"2 when e-+0, where E is a parameter of anisotropy. The influence of shape and elongation on the saturation coverage 0(03) is also discussed. Finally, for very elongated objects, we derive from scaling arguments that when the aspect ratio a of the objects becomes infinite, e(00) goes to zero according to a power law a-4 where p= l/(1+2fl). The fractal dimension of the system of adsorbed needles is also discussed.

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We investigate the initial stages of hen egg-white lysozyme (HEWL) adsorption at a charged solid interface using Brownian Dynamics simulation. The protein is modeled at the atomistic level and the adsorption surface is represented by a planar array of positively charged sites. Adsorption reactions are simulated at neutral pH and at low and high salt concentrations. We find that the HEWL, which has a net positive charge, can adsorb onto the positively charged surface. The results are consistent with an electrostatically driven adsorption process. While the orientational distribution of the adsorbed protein is nonuniform, there is no dominant patch composed of two or more oppositely charged residues. The electric field distribution around the protein is the best predictor of the adsorption behavior.