Phase-State Dependent Silica Nanoparticle Uptake of Giant Unilamellar Vesicles

Abstract

We quantify endocytosis-like nanoparticle uptake of model membranes as a function of temperature and therefore phase state. As model membranes, we use giant unilamellar vesicles consisting of 1,2-dipentadecanoyl-sn-glycero-3-phosphocholine (15:0 PC). Time-series micrographs of the vesicle shrinkage show uptake rates that are a highly non-linear function of temperature. A global maximum appears close to the main structural phase transition at T = Tm + 3 K, and a minor peak at the pretransition T = Tp = 22 °C. The quality of the kinetics linear fits reveals a deviation from the linear trend at the vesicle shrinkage peaks. To further elucidate the origin of the shrinkage peak, we performed force spectroscopy on a supported lipid bilayer. The results indicate a collapse of the adhesion energy at the structural phase transition. Further using literature results on the bending modulus as function of temperature and Helfrich’s model, this allows us to make qualitative conclusions on the membrane tension as function of temperature.