Credit: © 2006 Wiley

Quantum dots (QDs) are highly fluorescent inorganic nanoparticles that show significant promise as biological probes. By incorporating QDs into the bilayer membrane of lipid vesicles, researchers in Switzerland have investigated how these nanocontainers interact with live cells.

Horst Vogel and co-workers1 at the Ecole Polytechnique Fédérale de Lausanne and the Université de Lausanne used phospholipid molecules to prepare spherical vesicles in the presence of CdSe QDs. Fluorescence imaging and diffusion measurements indicated that the QDs are located only in the shell of the vesicles and not the interior. Significantly, the choice of phospholipids affected how these ensembles interacted with live cells. Those prepared from a mixture of two small-molecule lipids were transferred whole into the cells. In contrast, when a small amount of a phospholipid bearing a long polymeric chain was added to the mixture, the resulting vesicles were observed to fuse with cell membranes.

This fusion process allows for the selective delivery of two different cargoes to two specific regions of the cell. The QDs are integrated into the cell membrane whereas any species initially carried inside the vesicle — Vogel and co-workers use calcium ions as a model — is transferred into the cytoplasm. Although unmodified QDs are toxic, these vesicles did not show any cytotoxic effects, and combined with the potential to control their interaction with cells, these nanocontainers may be promising candidates for targeted drug delivery.