Modification of solid substrates by controlled adsorption of macroions

Mechanisms of cationic macroion adsorption on negatively charged solid substrates comprising mica and silica were thoroughly discussed. Attention was focused on poly(allylamine hydrochloride) (PAH), poly(dimethyl-diallylammonium chloride) (PDDA) and poly-L-lysine (PLL) widely used in practice. The bulk physicochemical parameters controlling the macroion adsorption such as the diffusion coefficient, hydrodynamic diameter, intrinsic viscosity and electrophoretic mobility were discussed. The latter, experimentally accessible parameter, enables to determine the electrokinetic charge of macroion molecules, their isoelectric points and zeta potentials. On the other hand, the analysis of the hydrodynamic diameter and the intrinsic viscosity data confirmed a largely elongated shape of the molecules even for concentrated electrolyte solution. These results are used for a quantitative interpretation of macroion adsorption at solid substrates investigated using in situ streaming potential measurements. It is confirmed that the macroion mostly adsorb in the side-on orientation forming layers whose maximum coverage can be regulated by the ionic strength of the solution. This streaming potential method can also be used to determine the stability of the layers performing controlled desorption kinetic measurements. It is shown that at pH 7.4 the PDDA and PLL macroions form stable layers on solid substrates, which can be used for an efficient immobilization of negatively charged macroions and bioparticles comprising protein molecules and viruses.