Gold nanoparticles in a two-dimensional (2D) array in water have potential to be useful in techniques such as surface enhanced Raman spectroscopy (SERS). Our lab has developed a new strategy to prepare water-stable 2D gold nanoparticle arrays by embedding the particles into the interior of peptoid nanosheets. Nanosheets are synthesized through the creation of monolayers and the disruption of the oil-water interface, leading to collapse into a bilayer sheet, similar to the phospholipid bilayer of a cell. Gold nanoparticles remain trapped in the hydrophobic center between the two monolayers of peptoids. Previous studies monitored the insertion of 5 nm particles functionalized with dodecanethiol ligands (each is 12 carbons long) into the nanosheet interior. These studies suggested that the interparticle gap distance, and thus plasmonic properties, could be controlled with the bulk nanoparticle concentration and potentially the length of the ligand. In this study, we carefully monitored the interparticle gap distance of 5 nm particles functionalized with hexadecanethiol ligands (each is 16 carbons long). Peptoid nanosheets were made with differing nanoparticle concentrations in order to determine ideal concentrations for monolayer collapse at the oil-water interface and for nanosheet synthesis. The peptoid nanosheets were then examined with the use of UV-visible spectroscopy as well as light microscopy to determine the packing density of the particles in the sheets. We expect the minimum interparticle gap distance achievable with the hexadecanethiol-functionalized particles will be larger than that observed with the dodecanethiol-functionalized particles (~ 3 nm). This general strategy to produce tunable, water-stable 2D arrays of gold nanoparticles can open doors for future nanomaterial-based detection applications.

Hexadecanethiol-functionalized gold nanoparticle dispersion in peptoid nanosheets

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