Cationic bilayers over silica: adsorption and colloidal stability at low ionic strength / Bicamadas catiônicas em sílica: adsorção e estabilidade coloidal a baixa força iônica

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

The study of adsorption of model-membranes on the surface of solid partic1es is an important line of research in rapidly developing research areas such as biosensors design, building up of immunological kits or design ofbiocompatible materiais. In this work, interactions between hidrophilic silica particles and cationic liposomes made up of dioctadecyldimethylammonium bromide (DODAB) were evaluated from a physicochemical point of view. The challenge of breaking open rigid bilayer vesicles upon contact with silica particles was circumvented by using a dioctadecyldimethylammonium bromide (DODAB) dispersion consisting of open, nanosized bilayer fragments instead of vesicles. At low ionic strength and pH 6.5, DODAB adsorption from bilayer fragments on silica was quantified from adsorption isotherms at 0, 0.1, 0.5,1.0 and 10.0 mM KCI. Adsorption increased as a function of KCI concentration and surface charge density on particles. Isotherms shape was typical of competitive adsorption with a maximum possibly due to hydrophobic attraction between adsorbed and free bilayer fragments. Upon adsorption as fiat patches on particles, the fragments did not apparently seal into a continuous and closed bilayer surrounding the particle, instead interacted via hydrophobic edges with free fragments in dispersion. At pH 6.5, over a range of DODAB (0 - 1.0mM) and KCI concentrations (0.1 - 10.0 mM), from particle sizing, zeta-potential analysis, photographs of the mixtures and particle sedimentation kinetics, colloid stability of particles in the mixtures was govemed by the ratio R of total surface areas for bilayers Ab and partic1es Ap, R= Ab/Ap. At R ~ 0.5, mean zeta-potential ( ζ ) was zero, mean particle diameter (Dz) was at maximum, sedimentation was rapid and colloid stability was at minimum; at R >1, ζ was positive, Dz was minimized, sedimentation was absent and colloid stability was high. At low ionic strength ([KCI] <10 mM), high colloid stability for particles in presence of cationic bilayer fragments was achieved at or above R=I, i.e., from the equivalence of total surface areas for bilayer fragments and particles.

ASSUNTO(S)

adsorption colloidal lipid pilayer partículas adsorção de membranas silica particle dodab dodab bicamadas sílica

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