Biophysical interactions between engineered nanoparticles and biomimetic model membranes: nanotoxicology and synthetic biology applications

Engineered nanoparticles (NPs) are nanoscale materials with unique physicochemical properties compared to bulk materials which provide novel and still largely unknown ways of interaction with biological systems. Since the gateway to the cell is the plasma membrane, understanding the interplay between NPs and membranes is a primary step towards understanding the behaviour of nanomaterials within biological systems. In this thesis, advanced spectroscopy and fluorescence microscopy techniques are employed to study the responses of large unilamellar lipid vesicles (LUVs) and giant unilamellar lipid vesicles (GUVs), respectively, to the interaction with silver NPs (AgNPs) and silica NPs (SiO2 NPs). Beyond the physicochemical properties of NPs and the membrane, the conditions of the medium also play a fundamental, but often overlooked, role in the NP-membrane interactions. Here, we provide evidence of the influence of the ionic strength of medium on the colloidal stability and membrane interactions of AgNPs, showing that at physiological ionic strength conditions AgNPs form small aggregates which display enhanced membrane activity. In a following investigation, we show that albumin proteins suspended in the medium adhere to the surface of SiO2 NPs reducing the adhesion energy between the NPs and the membrane and consequently inducing major changes in the interaction mechanisms. The ability of NPs to interact with lipid membranes also offer the prospect of using these nanomaterials in synthetic biology to develop membrane remodelling tools simpler and more robust than natural protein complexes. As an example, here we present 30 nm SiO2 NPs as a protein-free membrane fusion system. We propose a mechanistic model to explain the NP-triggered fusion according to which the non-specific interaction between 30 nm SiO2 NPs and lipid vesicles generates the right membrane curvature and tension conditions needed for the membranes to fuse. Finally, we use these NPs to build phase separated GUVs by fusing two single-phase vesicles. This represents a proof of increased membrane complexity achieved via membrane fusion. Moreover, membrane intermediate states during these fusion events reveal interesting phase dynamics involving the formation of transient asymmetric domains and interleaflet coupling processes. These initial observations can inspire future research programs focused on the development of novel-NP-based strategies to mimic protein functions.