Reversible phase transfer of quantum dots by gas bubbling

Amine-capped, lipophilic CdSe/ZnS quantum dots can be transferred in the presence of a switchable surfactant, specifically N′-oleyl-N,N-dimethylacetamidine, from an organic phase to water and then reverted to the organic phase simply by the addition/removal of carbon dioxide. The strategy is based on interdigitation of the surfactant between the non-polar ligands of the nanoparticles. The reversibility of the phase transfer is possible in at least ten cycles, after which the initial quantum dots, with their optical features preserved, can be recovered by simple precipitation in methanol, followed by centrifugation. This approach is most appealing, since external stimulus (carbon dioxide bubbling) could be obtained from a waste product, which is easily removed from the system by nitrogen bubbling. This article contains supporting information that will be made available online once the issue is published.