Interfacial Properties of Mixed DPPC-Hydrophobic Fumed Silica Nanoparticle Layers

The combination of interfacial thermodynamic, dilational rheology, and Brewster angle microscopy (BAM) has allowed the evaluation of the effect of hydrophobic fumed silica nanoparticles on the interfacial properties of Langmuir monolayers of 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC). Fumed silica particles modify the surface pressure-area (II-A) isotherm of DPPC, modifying both the phase behavior and the collapse conditions. These modifications are strongly dependent on the relative quantity of DPPC and Nanoparticles initially spread at the air-water interface. The incorporation of nanoparticles at the fluid interface alters the balance of interactions within the monolayer, thus leading to the disruption of the interfacial structure and consequently of the lipid packing. Measurements of dilational viscoelastic modulus against the frequency have been carried out by the mean of the oscillatory barrier method at different degrees of compression of the monolayer. The dynamic response is also modified by the presence of increasingly amount of nanoparticles at the interface. DPPC, being a lipid generally used as classical model for the study of biological relevant systems, the results here obtained can be used to deepen on the understanding of the effects of nanoparticles on the interfacial properties of biosystems.