Significance of particle size and charge capacity in TiO2 nanoparticle-lipid interactions

The activity of submicron sized titanium oxide (TiO2) particles towards biomembrane models is coupled to their charge carrying capacity and their primary particle size. Experiments: Electrochemical methods using a phospholipid layer on mercury (Hg) membrane model have been used to determine the phospholipid monolayer activity of TiO2 as an indicator of biomembrane activity. The particles were characterised for size, by dynamic light scattering (DLS) and scanning electron microscopy (SEM), and for charge, by acid-base titration. Findings: TiO2 nanoparticles aggregate in 0.1 mol dm-3 solutions of KCl. The charge capacity of TiO2 nanoparticles depends on their primary particle size and is unaffected by aggregation. TiO2 particles of ~40 nm primary particle size interact significantly with phospholipid layers. Aggregation of these particles initially has a small effect on this interaction but long term aggregation influences the interaction whereby the aggregates penetrate the lipid layer rather than adsorbing on the surface. Fulvic acid does not inhibit the ~40 nm particle/phospholipid interaction. P25 TiO2 particles of larger particle size interact less strongly with phospholipid layers and the interaction is alleviated following particle aggregation. The semiconductor properties of TiO2 are evident in voltammograms showing electron transfer to TiO2 adsorbed on uncoated Hg.