Investigation of the effects of titanium dioxide and cerium oxide nanoparticles on liposomes using fluorescent dye leakage

Nanoparticles are common additives in many consumer products and medicines, including foods, toothpaste, and other personal care items. Despite their ubiquity, there has been limited research into the disruptive effect of nanoparticles on biological membranes. Using synthetic liposomes as model membranes, we used fluorescent dye leakage to analyze the effects of two types of nanoparticles: titanium dioxide nanoparticles, which are used to whiten and brighten products, and cerium nanoparticles, which have shown promise as biological anti‐oxidants. Liposomes were formed from different types of purified lipids using the extrusion method. The pH‐dependent dye fluorescein was trapped inside the liposomes, which was maintained at pH 10 by a glycine buffer, while the buffer outside the liposomes was maintained at a neutral pH where the dye would be quenched. By monitoring the fluorescence emission intensity of the liposome solution as nanoparticles were added, it was possible to determine rates of leakage as a function of NP concentration, solution temperature, and NP diameter. Controls were performed in the absence of nanoparticles and in the presence of known membrane disruptors such as detergents. In conclusion, we have developed an assay to investigate the disruption of lipid bilayers by nanoparticles. Preliminary results from the assay indicate that low micromolar concentrations of nanoparticles increase the rate of dye leakage from the liposomes by more than a factor of two, consistent with particle interaction and membrane disruption. These results will be presented in the context of a larger, ongoing study that investigates mutagenicity and cytoxicity of nanoparticles. Support or Funding Information Defense Threat Research Agency