Unraveling the amino-acid mediated aggregation behavior of citrate-functionalized gold nanoparticles.

Citrate-capped gold nanoparticles are investigated in different solvent conditions and in the presence of single amino acids. Of specific interest is the aggregation behavior of the capped nanoparticles and the comparison of this behavior in different conditions and different capping densities. Using Coarse-grained Molecular Dynamics simulations, we could identify three aggregation modes of the nanoparticles in an aqueous environment with and without the presence of the amino acids. These modes were directly assigned to the distinct physical properties of the amino acids and are also influenced by the solvent environment and the ionic concentration, providing linear trends. By analyzing the underlying mechanisms, dynamics, as well as the statistical and thermodynamic properties of the complex nanoparticle-functionalization-salt-amino acid system, we provide important molecular level insights. These are discussed in the context of amino acid detection and the use of functionalized nanoparticles for biomedical applications.