Interaction between nanostructured materials and synthetic and plasmatic membranes

Understanding the interplay between nanostructured materials and cell membranes is the basis of their possible usage for therapeutics and for engineering new bio-applications. With the aim to unravel the mechanisms of interaction at the molecular scale, I have studied during my PhD the interaction between CdSe/CdS semiconductor nanorods (NRs) and polymeric micelles with model and plasmatic lipid membranes. NRs were in-house synthetized and functionalized with different amount of bis-amino polyetilenglycol (PEG) and a tertiary amine to tune their surface potential (ζ) between -50 mV and +10 mV. Their interaction with lipid mixtures of different composition in form of supported lipid bilayers (SLBs), lipid monolayers (LMs) and different in vitro cell lines was tested. In particular, NRs adsorption to SLBs was monitored by quartz crystal microbalance with dissipation monitoring (QCM-D) varying lipid mixtures charge and investigating the influence of gel phase domains; interactions with LMs same in composition as SLBs were measured by surface pressure-area isotherms. Results showed that tuning the mutual properties of the system regulates the interaction with NRs on the membranes and that the increase of membrane complexity inhibits it: in particular a strong interaction was registered with fluid state membranes and NRs opposite in charge when Δζ > 70 mV, whereas the interaction was hindered in presence of gel phase domains. LMs models gave more detailed information, showing removal of lipid molecules from air-water interface or insertion of NRs between lipids according to the overall system charge. QCM-D and surface pressure-area isotherms results were in agreement. Since the polymer coating of the NRs was shown to regulate the interaction, in order to elucidate its effect I have employed also fluorescent polymeric micelles of different dimension (60 and 300 nm in diameter). I have tested the interaction of both NRs and micelles with different cell lines, namely post-natal mouse neuronal network (known to have a dynamically changing membrane potential), mouse neuroblastoma Neuro2a (that can differentiate in neuronal-like cells) and Chinese hamster ovary cells (epithelial, with a static membrane potential), using confocal microscopy both on fixed samples and in real time. Preliminary results showed adhesion of negatively charged NRs and micelles on both dynamic potential membrane cell lines. Again a threshold value was found for NRs interacting with neurons (ζNR < -18 mV), similarly to what was observed with models. A neurotoxin was then introduced in the experiments, to reduce the spikes of the active cells. A satellite project is finally presented as a full paper at the end of the thesis. The project concerns the fabrication and characterization of thin anodic porous alumina (tAPA) substrates, which surface was made surface-enhanced Raman spectroscopy (SERS) -active by coating with a thin gold (Au) layer. My part in this project was related to the monitoring of the chemisorption of thiols and the formation of SLB models from lipid vesicles by using the QCM-D technique on Au substrates.