Dynamic Surface Properties of Mixed Dispersions of Silica Nanoparticles and Lysozyme

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Abstract
The surface properties of mixed aqueous dispersions of lysozyme and silica nanoparticles were studied using surface-sensitive techniques in order to gain insight into the mechanism of simultaneous adsorption of protein/nanoparticle complexes and free protein as well as the resulting layer morphologies. The properties were first monitored in situ during adsorption at the air-water interface using dilatational surface rheology, ellipsometry and Brewster angle microscopy. Two main steps in the evolution of the surface properties were identified. First, the adsorption of complexes did not lead to a significant deviation of the dynamic surface elasticity and dynamic surface pressure from those for a layer of adsorbed lysozyme globules. Second, through gradual displacement of protein globules from the interfacial layer as a result of the further complex adsorption, the layer became more dense with much higher dynamic surface elasticity (~ 280 mN/m compared with ~ 80 mN/m for a pure protein layer). These layers were shown to be fragile and could be easily broken into separate islands of irregular shape by a weak mechanical disturbance. The layer properties were then monitored following their transfer to solid substrates using atomic force microscopy and scanning electron microscopy. These layers were shown to consist of nanoparticles surrounded by a rough shell of protien globules while some particles tended to form filamentous aggregates. This comprehensive study provides new mechanistic and morphological insight into the surface properties of a model protein/nanoparticle system, which is of fundamental interest in colloidal science and can be extended to systems of physiological relevance.
Funding Information
  • Russian Foundation for Basic Research (18-33-00015, 19-53-52006)

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