23 Mai – Thesis defense - Arantza Zavala Martinez

14 h Amphi Adolphe Pacault - CRPP (Pessac)

Dynamics of self-assemblies of rod-like viruses and spherical gold nanoparticles: from matchstick-like particles to colloidal stars.

In this thesis, we report on the study of the self-diffusion of hybrid gold-virus self-assemblies formed by spherical gold nanoparticles and rod-like viruses. For this purpose, we use genetically modified mutants of filamentous bacteriophages which possess disulfide groups (Cys-Cys) exposed at their proximal end. The presence of a disulfide bridge allows them to bind to metal nanoparticles by one of their tips forming a weak covalent bond. The control of the resulting self-assembled structures is achieved by tuning the molar excess of viruses with respect to nanoparticles. When both components are set in similar proportion, their interaction leads to the formation of matchstick-like particles composed by a 1 µm long virus attached by its tip to a single gold nanobead. However, if the viruses are in high excess, the resulting structures are colloidal stars formed by multiple viruses attached to a single gold nanobead.
The Brownian dynamics of these structures is characterized in dilute and dense regimes both by Dynamic Light Scattering (DLS) and single particle tracking through optical microscopy. An advantage of using both techniques resides in the possibility to study separately the different components forming the hybrid particles. Specifically, the high scattering signal coming from the gold nanoparticle facilitates the determination of the dynamic properties of the structure by observing mostly the bounded bead, whereas the labeling with fluorescent dyes allows the direct determination of the virus diffusion coefficient by microscopy.
Our findings on the self-diffusion of the matchstick-like particles as a function of the nanoparticle size evidence the flexibility of the virus-bead link. Considering the intrinsic asymmetry of the matchstick-like structure, the possibility to induce self-propulsion has been investigated in order to get active hybrid particles by overcoming their Brownian motion thanks to light or chemical fuels.
We quantitatively study the self-organization and diffusion of the colloidal stars as a function of the volume fraction. When the later increases, a progressive dynamical arrest related to the interdigitation of the star viral arms is observed suggesting a glassy state in the dense regime.
In the last part of this thesis, we construct optimized new mutants of filamentous bacteriophages which are engineered to bind metal nanoparticles to both tips. This results in the development of novel hybrid superstructures with more versatile design.

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