Delivery of cationic quantum dots using fusogenic liposomes in living cells

Quantum dots (QDs) are fluorescent nanocrystals that present unique optical properties, especially a high photostability. However, their use for intracellular studies is still limited since their passage through the living cell membranes does not occur passively. In this work, we adapted the ethanol injection method to encapsulate cationic hydrophilic QDs into fusogenic liposomes, to deliver them in living cells. Liposomes were characterized using zeta potential, dynamic light scattering (DLS), fluorescence microscopy and transmission electron microscopy (TEM). Red blood cells (RBCs) were applied as models in this study to probe the liposome fusion with the cell membrane since RBCs do not present endocytic activity. Therefore, HeLa cells were also applied to test the QDs delivery by the liposomes. The TEM and the fluorescence microscopy confirmed the QDs encapsulation, with an efficiency of 43%, determined by UV vis spectroscopy. Zeta potential showed that the QDs-loaded fusogenic liposomes were positively charged and presented an average size of 343 nm, determined by DLS. Furthermore, fluorescence microscopy analyses of RBCs and HeLa cells confirmed the liposomes fusion with the cell membrane and suggested the release of QDs into cells. Thus, we expect that this work will contribute to improve the use of QDs as fluorescent probes to intracellular studies.