| Summary: | Controlling gold nanoparticles (GNPs) surface chemistry is a fundamental prerequisite to tailor their properties and envision their assembly into complex nanomaterials from a “bottom-up” approach. Short peptides have been specifically designed to form self-assembled monolayers on GNPs surface and used to increase their stability. However, their structural characterization is often poorly investigated and challenging to assess. This body of work examines different approaches to elucidate the structure and organization of peptide self-assembled monolayers on GNPs. First, the current knowledge and the methods available to characterize the GNPs surface are reviewed. Second, the attempt at using benzophenone-derivative peptides, to provide insights into the molecular organization and compactness of mixed monolayers self-assembled on GNPs, is reported. Under irradiation at 350 nm, the carbonyl group of the benzophenone moiety crosslinks to an adjacent molecule. However, the photo-cross-linking reaction, monitored by FTIR spectroscopy in solution, was not detected on the GNPs surface. Third, to probe the accessibility of a functional group at the GNPs surface, fluorescently labelled peptides, quenched when bound to the gold surface, and bearing a cleavage site for thrombin enzyme at different positions along the chain, were inserted into different peptide self-assembled monolayers on GNPs. The timings of the increase in fluorescence, upon cleavage by thrombin, probed the accessibility, and hence the molecular environment, of the site within the different monolayers investigated. Fourth, a computational model for peptide-capped GNPs was developed using experimentally characterized CALNN- and CFGAILSS-capped GNPs as a benchmark. The molecular dynamics simulations not only reproduced the experimentally observed dependence of the monolayer secondary structure on peptide capping density and on nanoparticle size, but provided also further insights into the monolayers and inter-peptide interactions at the molecular level.
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