Dispersion and stability studies of resorcinarene-encapsulated gold nanoparticles

Two resorcinarene surfactants with sulfur-functionalized headgroups have been evaluated for their ability to stabilize dispersions of midnanometer (16-87 nm)-sized gold particles in organic solvents. Citrate-stabilized colloidal gold nanoparticles were extracted from aqueous solutions into toluene or chloroform by tetrabenzylthiol resorcinarene 1 or tetraarylthiol resorcinarene 2. The nanoparticle dispersions were subjected to various conditions and monitored for changes in plasmon absorption intensity. The stability of the dispersions was dependent on the chemisorptive properties of the surfactant headgroup, with tetrabenzylthiol 1 being the more effective dispersant. Nanoparticles encapsulated by 1 were also highly robust, demonstrated good resistance to alkanethiol-induced flocculation, and could be redispersed after repeated precipitations in polar solvents. Surface-enhanced Raman scattering analysis and X-ray photoelectron spectroscopic studies confirmed significant differences in the chemisorptive properties of tetrathiols 1 and 2, indicating that surface passivation is an important factor in the dispersibility of colloidal gold nanoparticles in nonpolar solvents.