Metal nanoclusters composed of primary nanoparticles are of great interest in various advanced applications, including biomedical imaging, catalysis, and imaging subsurface reservoirs.  Recently, we demonstrated a new colloidal synthesis to make reversible monodisperse self-limited clusters of nanoparticles in the range of 20-100 nm in less than a minute from 5 nm GSH-capped Au NPs by balancing short-ranged attraction against long-ranged repulsion.  The size of the clusters could be tuned simply by controlling the pH, primarily to vary the short-ranged attraction between the glutathione molecules on the surface rather than the long-ranged repulsion between particles. For example, as the pH is lowered from 5.4 to 3.8, partial protonation of GSH anions to form a mixture of anions and zwitterions increased the hydrogen bonding between GSH markedly resulting in an increase in the hydrodynamic diameter of the clusters from 20 to 100 nm.  This change is far greater than would be expected from the change in long-ranged electrostatic repulsion, given a small change in the zeta potential.  The clusters fully dissociate to primary Au NPs upon raising the pH to 7 to break the hydrogen bonds between the GSH molecules, but on a slower time scale of ~ 1 hour.  The slower time scale for dissociation versus association may be attributed to greater attraction between a nanoparticle and a cluster versus that between two nanoparticles.<br/> Although the low zeta potential of the GSH-capped Au clusters (&lt;10mV) was enough to provide long-ranged repulsion for self-limited growth at time scales less than several hours, the electrostatic repulsion between the clusters was too weak to prevent aggregation between clusters at longer time scales. With the addition of small amount of amounts of charged citrate to the GSH coated nanoclusters (for example 1/1 CIT/GSH), the time scale of cluster-cluster aggregation was lengthened, such that the hydrodynamic diameter of the clusters was constant for 1 day. This greater stability of the clusters may be explained by the greater charge (electrostatic repulsion) of the clusters and reduced GSH-GSH interactions upon adsorption of citrate.<br/>

Reversible self-assembly of monodisperse gold nanoparticle clusters in aqueous solution via pH-tunable interactions between surface ligands

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.