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Luminescent semiconductor nanocrystals, also known as quantum dots (QDs), have rich surface chemistry and unique optical properties that make them useful as probes or carriers for molecular diagnostics and therapeutics. However, their potential toxicity and instability in biological environments have puzzled scientific researchers. Much research effort has been devoted to encapsulation of QDs with liposomal hybrids to make them versatile nanocarriers for simultaneous therapeutics and diagnostics (theranostics) and considerable progress has been made over recent years. We provide an overview of the use of QD-liposome complexes (QLCs) for imaging applications, in particular applications in theranostics. More specifically, the design considerations, intracellular uptake and tissue-specific targeting of QLCs are highlighted. Current findings of QLCs for theranostics are discussed. We also discuss the challenges and highlight future directions for applications of liposome-QD hybrid nanocarriers in the biomedical arena.

The cationic dimethyldioctadecylammonium/trehalose 6,6,9-dibehenate (DDA/TDB) liposome is as a strong adjuvant system for vaccines, with remarkable immunostimulatory activity. The mucosal administration of vaccines is a potential strategy for inducing earlier and stronger mucosal immune responses to infectious diseases. In this study, we assessed whether the intranasal administration of cationic DDA/TDB liposomes combined with influenza antigen A (H3N2) can be used as a highly efficacious vaccine to induce mucosal and systemic antibody responses. Confocal laser scanning microscopy and a flow-cytometric analysis showed that the uptake of the cationic DDA/TDB liposome carrier was significantly higher than that of neutral 1,2-distearoyl-sn-glycero-3-phosphocholine/cholesterol (DSPC/Chol) or cationic 1,2-dioleoyl-3-trimethylammonium-propane/3β-(N-[N′,N′-dimethylaminoethane]-carbamoyl (DOTAP/DC-Chol) liposomes. Our results indicate that the cationic DDA/TDB liposome is more effective in facilitating its uptake by dendritic cells (DCs) in vitro than the DSPC/Chol or DOTAP/DC-Chol liposome. DCs treated with DDA/TDB liposomes strongly expressed CD80, CD86, and MHC II molecules, whereas those treated with DSPC/Chol or DOTAP/DC-Chol liposomes did not. C57BL/6 mice intranasally immunized with H3N2-encapsulating cationic DDA/TDB liposomes had significantly higher H3N2-specific s-IgA levels in their nasal wash fluid than those treated with other formulations. The DDA/TDB liposomes also simultaneously enhanced the serum IgG IgG2a, IgG1, and IgG2b antibody responses. In summary, DDA/TDB liposomes effectively facilitated their uptake by DCs and DCs maturation in vitro, and induced significantly higher mucosal IgA, systemic IgG, IgG1, and IgG2b antibody titres than other formulations after their intranasal administration in vivo. These results indicate that DDA/TDB liposomes are a promising antigen delivery carrier for clinical antiviral applications. [ABSTRACT FROM AUTHOR]