How does the surface chemistry of gold nanoparticles change when they are transferred into natural environments?
Gold nanoparticles (Au NPs) are currently the subject of research efforts focused on developing highly sensitive sensors, diagnostic techniques, and targeted drug therapies. As these NPs move from the research lab to large-scale production, they will inevitably be released into the environment. This project sought to explore the eventual fate of these nanoparticles after release into the environment. The stability of gold nanoparticles capped with three typical ligands was examined in solutions that mimicked natural environments: artificial seawater, locally gathered creek water, and a humic acid organic sediment standard solution. Zeta potential measurements and UV/Vis spectroscopy were used to assess the stability of the NPs. The zeta potential of all tested NPs moved closer to zero when resuspended in the creek water, indicating that either the capping agents had been replaced or overcoated by neutral molecules in the water. The seawater caused all the particles’ zeta potentials to move closer to zero, which may be an effect of the high ionic strength of the solution. The humic acid solution caused a decrease in zeta potential for two out of three capping agents, likely due to the adsorption of carboxylic acids in the humic acid onto the NP surfaces.