Biomedical Engineering Reference
In-Depth Information
Zhang et al. developed a method to increase the biocompatibility of CdSe/ZnS
QDs (Zhang et al. 2006b ). The surface of CdSe/ZnS core-shell QDs was first
silanized and then coated with PEG to reduce the toxicity of nanocrystals to the
cells. The results showed that the gene expression of fibroblasts changed when they
were exposed to silica-coated QDs. Burgess et al. showed that QDs could be cova-
lently conjugated to pDNA for transfection studies (Srinivasan et al. 2006 ).
Transfection studies on QD-DNA conjugates and Lipofectamine 2000 showed maxi-
mum cellular uptake at 6 h, with approximately 75% of the DNA located in the
cytoplasm and 25% in the nucleus. After 10 h, approximately 2/3 of the DNA was
in the nucleus of the cells, and this nuclear localization was proportional to gene
expression. Ho et al. developed a QD-FRET (Förster resonance energy transfer)
system to investigate the structural composition and dynamic behavior of polymeric
DNA nanocomplexes intracellularly (Ho et al. 2006 ; Chen et al. 2008 ). In these stud-
ies, pDNA encoding GFP was biotinylated using PEI-psoralen-biotin, and these
analogues were conjugated to streptavidin-functionalized QDs. The QD-labeled
DNA was complexed with Cy5-labeled chitosan and introduced into HEK293 cells.
The trafficking of the complexes within cells was monitored using confocal micros-
copy. At 24 h after transfection, the intact complexes were localized around the cell
nucleus. At 48 h after transfection, most complexes released DNA molecules. At 72,
QD-labeled DNAs could be observed within the nucleus of a cell expression GFP.
This study illustrated that QD-FRET-enabled detection of nanoplexes stability com-
bined with image-based quantification is a valuable method for investigating mecha-
nisms involved in nanoplexes uptake and intracellular trafficking.
QD-labeling has also been utilized by Bhatia et al. for gene silencing by siRNA
(Chen et al. 2005a ). In this study, QDs were introduced as a traceable marker to shed
light on the siRNA delivery. However, cationic transfection agents (Lipofectamine
2000, superfect, or translocation peptide) were required to promote gene transfer,
indicating that the QDs worked only as a labeling moiety. Subsequently, Bhatia
et al. functionalized QDs with both siRNA and the tumor-targeting F3 peptide
(Derfus et al. 2007 ). In HeLa cells, these tumor-targeting QD-siRNA conjugates
showed up to ~29% EGFP gene knockdown when cellular uptake was followed by
the addition of an endosome escape agent (Lipofectamine 2000). Additionally, Tan
and coworkers ameliorated the chitosan-based transfection system by doping with
QDs for siRNA tracking (Tan et al. 2007 ). Recently, Gao's group developed both
the proton-sponge-coated and amphipol-modified QDs to further enhance the deliv-
ery efficiency (Qi and Gao 2008a ).
5.6
Calcium Phosphate Nanoparticles
Calcuim phosphates (CaP) are the inorganic components of biological hard tissues,
for example, bone, teeth, and tendors. Because the calcium phosphates usually have
a high biocompatibility and a good biodegradability compared to other types of
nanomaterials, they are extremely attractive for gene therapy applications. Relying
Search WWH ::




Custom Search