Reversible Self-Assembly of Glutathione-Coated Gold Nanoparticle Clusters via pH-Tunable Interactions.

Nanoparticle (NP) clusters with diameters ranging from 20 to 100 nm are reversibly assembled from 5 nm gold (Au) primary particles coated with glutathione (GSH) in aqueous solution as a function of pH in the range of 5.4 to 3.8.

Control of Primary Particle Spacing in Gold Nanoparticle Clusters for Both High NIR Extinction and Full Reversibility.

Reversible NIR-active nanoparticle clusters with controlled size from 20 to 100 nm were assembled from 5 nm gold nanoparticles (Au NP), with either citrate (CIT) or various binary ligands on the surface, by tuning the electrostatic repulsion and the hydrogen bonding via pH. The nanoclusters were bound together by vdW forces between the cores and the hydrogen bonds between the surface ligands and dissociated to primary nanoparticles over a period of 20 days at pH 5 and at pH 7. When high levels of citrate ligands were used on the primary particle surfaces, the large particle spacings in the nanoclusters led to only modest NIR extinction.

Formation of Small Gold Nanoparticle Chains with High NIR Extinction through Bridging with Calcium Ions.

The self-assembly of citrate-capped Au nanoparticles (5 nm) resulted in branched nanochains by adding CaCl2 versus spherical nanoclusters for NaCl. These assemblies were formed between 1 s to 30 min by tuning the electrostatic repulsion and the interparticle bridging attraction between the cations and citrate ligands as a function of electrolyte concentration. For dilute Ca(2+), strong interparticle bridging favored particle attachment at chain ends.