Doxorubicin-loaded lipid-quantum dot hybrids: surface topography and release properties

A few studies have attempted to combine the physicochemical versatility offered by the liposome structure with the superior optical characteristics of quantum dots (QD) for the construction of multifunctional nanoparticles. We are reporting the construction of drug-loaded liposome-QD hybrid vesicles (L-QD) by incorporating TOPO-capped, CdSe/ZnS QD into the two types of lipid bilayers: the ‘rigid’ disteroylphosphatidylcholine (DSPC:Chol:DSPE-PEG₂₀₀₀) and a fluid-phase bilayer of egg PC (EPC:Chol:DSPE-PEG₂₀₀₀). Structural characterization of L-QD hybrid vesicles using atomic force microscopy (AFM) revealed that the incorporation of QD took place by hydrophobic self-association within the membranes. The encapsulation of hydrophilic small molecules in the internal aqueous phase of the L-QD hybrids showed different degrees of carboxyfluorescein (CF) release in buffer and serum, depending on the type of lipid used. The presence of QD in the lipid bilayer increased the CF release from EPC fluid bilayer. On the other hand, (DSPC) L-QD hybrids showed a higher stability under the same conditions with minimal CF leakage. Furthermore, (DSPC) L-QD hybrids showed a stable mean diameter up to three weeks stored at 4 °C, 25 °C, and 40 °C, determined by photo correlation spectroscopy (PCS) analysis. Finally, doxorubicin (Dox) was loaded into L-QD hybrids using the osmotic gradient technique and with at least 97% loading efficiency. The fluorescence spectrum of Dox was simultaneously detected with that of green-emitting QD that indicated the coexistence of QD and Dox in a single vesicle system. In conclusion, the drug-loaded L-QD-Dox hybrid vesicles presented here constitute a promising multifunctional delivery vector capable of transporting combinations of therapeutic and diagnostic modalities.