Incorporation of quantum dots into the lipid bilayer of giant unilamellar vesicles and its stability

We studied CdSe Quantum dot-Liposome Complexes (QLCs), which are GUVs (Giant Unilamellar Vesicles) incorporated with quantum dots (QDs) loaded into the DOPC lipid bilayer. QLCs were prepared by employing the electroswelling method combined with spin coating techniques. Hexadecylamine (HDA) coated CdSe QDs of five different sizes from blue- (radius ∼2.05 nm) to red-emission (∼3.5 nm) were used to examine what size of QDs can be loaded into the DOPC lipid bilayer. Blue (radius ∼2.05 nm), green (∼2.25 nm), and yellow (∼2.65 nm)-emission QDs were successfully inserted in the lipid bilayer. However, we did not observe any QLCs for the orange-emission QDs (∼3.0-3.15 nm) and red-emission ones (∼3.5 nm). This QD size dependence of the incorporation into the lipid bilayer is partly supporting the predictions in our published theoretical work. DOPC lipids showed a much smaller QLC yield than that of asolectin which is a mixture of many different kinds of lipids. Our model explains this large difference in the population qualitatively. The existence of QDs in the lipid bilayer at a nanometer scale was confirmed by employing laser-scanning confocal microscopy, Cryo-TEM, and negative staining and sectioning TEM.