Rapid separation and purification of nanoparticles in organic density gradients.

Nanoseparation and concomitant purification of nanoparticles by ultracentrifugation in a nonhydroxylic organic density gradient has been demonstrated by separating several typical colloidal nanoparticles, including Au, Ag, and CdSe. Successful separation of Au nanowires from their spherical counterparts showed that colloidal particles can be separated not only by size but also morphology. In addition to extending the range of colloidal systems which can be separated and providing monodisperse samples that cannot be obtained by synthesis optimization alone, this method simplifies the postsynthesis treatment process and facilitates subsequent bulk assembly of the monodisperse colloids. Dissolution of organic polymers in the gradient medium both enhances the separation efficiency and also allows the direct fabrication of functional composite films with discrete monodisperse nanoparticles embedded inside.