Janus nanoparticles as versatile phase-transfer reagents.

Janus nanoparticles were prepared by interfacial ligand-exchange reactions of hexanethiolate-protected gold (AuC6) nanoparticles with 3-mercapto-1,2-propanediol (MPD) at the air|water interface. As nanoscale analogues to conventional amphiphilic molecules, the resulting Janus nanoparticles were found to form oil-in-water micelle-like or water-in-oil reverse micelle-like superparticulate structures depending on the solvent media. These unique characteristics were exploited for the effective transfer of diverse guest nanoparticles between organic and water phases. The transfer of hydrophobic nanoparticles from organic to water media or water-soluble nanoparticles to the organic phase was evidenced by transmission electron microscopy, dynamic light scattering, UV-vis, and photoluminescence measurements. In particular, line scans based on energy-dispersive X-ray analysis showed that the vesiclelike structures consisted of multiple layers of Janus nanoparticles which encapsulated the guest nanoparticles in the cores. The results highlight the unique effectiveness of using Janus nanoparticles in the formation of functional nanocomposites.