Défense de thèse de doctorat en sciences physiques : "gold nanoparticles"

Study of the interactions between gold nanoparticles and models of cell membranes by second order nonlinear optical spectroscopies

Jury

Emmanuel BENICHOU (Univ. Lyon 1), Patricia LOSADA-PEREZ (UHasselt), Yves CAUDANO (UNamur), Benoît CHAMPAGNE (UNamur), Stéphane LUCAS, président (UNamur), Francesca CECCHET, promoteur (UNamur)

Résumé

In the last 20 years, new technologies based on nanoscale materials have drastically increased the exposure of humans to nanoparticles (NPs), either because of their use in many goods, such as paints, cleaning products, cosmetics, clothing, fuel additives, or as imaging contrast agents and drug-delivery carriers in several biomedical applications and diseases treatments, for example.

The goal of this thesis is to study the fundamental interactions driving NPs to adsorb, penetrate and/or alter the cell membrane structure with a new experimental approach, which exploits the selectivity of second order nonlinear optical phenomena, occurring when intense lasers light interacts with matter. The corresponding nonlinear optical spectroscopies own an uncommon sensitivity to nanometer-sized regions, as the one defined by the nanoparticles meeting the membrane. Elucidating the first contacts of NPs with membranes is consensually recognized as necessary to understand physiological responses and to predict biological effects.

In this thesis, the interface between nanoparticles and membranes has been reproduced and simplified by using lipid bilayers films of different composition and charges. A vibrational and an electronic second order nonlinear optical spectroscopy, respectively sum-frequency generation (SFG) and second harmonic generation (SHG), have been applied to the study of the aforementioned nano-bio-interfaces. By measuring the interfacial vibrational response, SFG spectroscopy has allowed highlighting the key role of the electrical charges at the interface in driving the interactions of functionalized gold nanoparticles (AuNPs) with cell membrane models. The vibrational signature of the water molecules surrounding the membrane has been directly measured; and from that, for the first time, the effects of the AuNPs on the organization of the membrane hydration layer have been experimentally observed. Moreover, the vibrational SFG signature of the membrane lipid molecules has allowed probing the damages to the membrane structure itself. Complementary, SHG spectroscopy has enabled a direct and real-time detection of the gold nanoparticles interacting with a membrane model, thus unravelling information on the effects of AuNPs size and charges on the interaction mechanisms.

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