The Effect of Peptoid Monolayers on Functionalized Gold Nanoparticle Film Assembly at the Oil-Water Interface

Gold nanoparticles (AuNPs) that are ordered in two-dimensional (2D) arrays have been shown to exhibit optoelectronic properties that make them useful in a variety of technologies, including sensors for pollutants. These properties depend on the way the particles are arranged within the array. Previous work has shown that AuNPs can be simply and inexpensively assembled into 2D arrays at fluid interfaces using a Langmuir trough, but controlling the exact patterning of the AuNPs at the interface remains a challenge. Our research focuses on controlling the assembly of hydrophobic AuNPs at fluid interfaces using amphiphilic peptoids that readily form highly ordered monolayers. To study whether peptoid monolayers effectively control the 2D assembly of dodecanethiol ligated and phenylethanethiol ligated 5nm AuNPs, we use the Langmuir-Blodgett method to transfer composite films from fluid surfaces to silicon thermal oxide wafers. The deposited films are then characterized using optical microscopy and AFM imaging. Preliminary results show that the AuNPs do not completely cover the peptoid monolayer, but instead assemble into regions in which they are densely packed. In these regions, the AuNP ligands integrate into the peptoid monolayer. The peptoid-AuNP composite films are more uniform than those of only peptoid or only nanoparticle, and the peptoid-dodecanethiol AuNP composite films demonstrate a more uniform film than those with phenylethanethiol AuNPs. The flower-like pattern observed with the peptoid-phenylethanethiol composite film is likely due to the pi-pi interactions between the peptoid and the phenylethanethiol AuNPs. Additionally, the increasing the concentration of dodecanethiol ligated AuNPs has been shown to create more uniform films than lower concentrations.