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Marianne Marchioni

Ecoconception of new biocidal agents based on silver nanoparticles with bio-inspired coating

Published on 15 October 2018

Thesis presented October 15, 2018

Silver nanoparticles are increasingly used in everyday consumer goods as well as in medical devices for their biocidal activity, which is due to the release of Ag(I) ions over time. The hindsight on these nano-objects and, in particular, on their safety is still not sufficient and studies on their transformation and their impact in vivo are currently an intense research field. Indeed, the fate in the body of macro- and micro-materials studied classically is not the same as for nanomaterials. The case of the silver nanoparticles illustrates this problem: the soluble silver injected intravenously is eliminated faster than the same amount of silver injected in nanoparticular form. Moreover, the concentration of silver found in the bloodstream and organs is ten times higher when silver nanoparticles are injected rather than ingested. The development of silver nanoparticle-containing implanted devices that get in direct contact with the body, must thus take into account the related risks. A Safer-by-design approach could be a way to solve this issue.

One of the main components of Safer-by-design development is the functionalization of nano-objects. The affinity of the thiolates for Ag(I) ions is very high, which would make thiolated ligands a good tool for silver nanoparticle functionalization. However, it is known that the thiolated molecules lead to different behaviors, ranging from the dissolution of silver nanoparticles into Ag(I) ions to the simple passivation of the surface of the nanoparticles, which leads to the loss of their biocidal activity.

The Ecodesign of New Biocidal Agents based on Silver Nanoparticles and Bio-inspired Coating is therefore at the interface of several research areas and its main objective was to lay down the conceptual foundations for the development of a Safer-by-design biocidal agent based on the interaction between silver nanoparticles and thiolated molecules.

The development of this project required to study the reactivity of various biological or bio-inspired thiolated molecules with silver nanoparticles. First of all, we have highlighted the importance of the architectural pre-organization of biomolecules in the dissolution kinetics, as well as the role of the number of free thiols in the molecule. In the case of molecules inducing the dissolution of the nanoparticles, its kinetic increases with the number of free thiols present on the molecule and with the pre-organization of the metal binding site. In a second time, the main project of this thesis was the development of a proof of concept of a new biocidal agent composed of silver nanoparticles bridged together via a symmetric tripodal thiolated ligand, which is the chemical mimic of one binding site of a metallothionein. These nanoparticle assemblies were active against bacteria (E. coli) and less toxic than silver nanoparticles on eukaryote cells (HepG2), despite a similar cellular entry. Finally, a screening was performed with polyethylene glycols having two to eight thiols and varying polymer lengths in an attempt to rationalize the differences in the behavior of silver nanoparticles in the presence of the thiolated molecules. This ongoing work leads to the observation of various behaviors that will enable to explore novel ways for the development of biocidal based on nanoparticles assemblies mediated by thiol – Ag(I) bonds.

Therefore, this overall PhD work allows performing both very fundamental researches concerning the reactivity of thiols with silver atoms at the surface of the nanoparticles and the development of products with application potential, silver nanoparticle assemblies that are Safer-by-design biocide.

Silver Nanoparticles, biocide, nanotoxicity

On-line thesis.