The role played by hydration forces in the stability of protein-coated particles: non-classical DLVO behaviour

An anomalous colloidal stability is observed when protein-covered particles are exposed to high salt concentrations, in opposite to the classical theory (DLVO) predictions. In hydrophilic systems some other discrepancies with respect to this theory has also been described in the literature and hydration forces are invoked to rationalize these phenomena. In our case, the dependence of the anomalous behaviour with pH and electrolyte ion concentration points to the specific adsorption of cations as responsible. An extension to the DLVO theory including hydration forces and its dependence with salt concentration is proposed. From the practical point of view, this stabilization mechanism is of great interest in the development of clinical latex immunoassays, which often suffer from colloidal stability problems.