Nanoparticle core properties affect attachment of macromolecule-coated nanoparticles to silica surfaces

Transport, toxicity, and therefore risks of engineered nanoparticles (ENPs) are unquestionably tied to interactions between those particles and surfaces. In this study, we proposed the simple and untested hypothesis that coating type can be the predominant factor affecting attachment of ENPs to silica surfaces across a range of ENP and coating types, effectively masking the contribution of the particle core to deposition behaviour. To test this hypothesis, TiO2, Ag0 and C60 nanoparticles with either no coating or one of three types of adsorbed macromolecules (poly(acrylic acid), humic acid and bovine serum albumin) were prepared. The particle size and adsorbed layer thicknesses were characterised using dynamic light scattering and soft particle electrokinetic modelling. The attachment efficiencies of the nanoparticles to silica surfaces (glass beads) were measured in column experiments and compared with predictions from a semi-empirical correlation between attachment efficiency and coated particle properties that included particle size and layer thickness. For the nanoparticles and adsorbed macromolecules in this study, the attachment efficiencies could not be explained solely by the coating type. Therefore, the hypothesis that adsorbed macromolecules will mask the particle core and control attachment was disproved, and information on the properties of both the nanoparticle surface (e.g. charge and hydrophobicity) and adsorbed macromolecule (e.g. molecular weight, charge density extended layer thickness) will be required to explain or predict interactions of coated nanoparticles with surfaces in the environment.