[en] Quantum dots (QDs) are semiconducting nanoparticles with photoluminescence properties that do not photobleach. Due to these advantages, using QDs for non-viral gene delivery has the additional benefit of being able to track the delivery of the genes in real time as it happens. We investigate the efficacy of mercaptopropionic acid (MPA)-capped CdSe aqueous quantum dots (AQDs) electrostatically complexed with branched polyethyleneimine (PEI) both as a non-viral gene delivery vector and as a fluorescent probe for tracking the delivery of genes into nuclei. The MPA-capped CdSe AQDs that were completely synthesized in water were the model AQDs. A nominal MPA:Cd:Se = 4:3:1 was chosen for optimal photoluminescence and zeta potential. The gene delivery study was carried out in vitro using a human colon cancer cell line, HT29 (ATCC). The model gene was a plasmid DNA (pDNA) that can express red fluorescent protein (RFP). Positively charged branched PEI was employed to provide a proton buffer to the AQDs to allow for endosomal escape. It is shown that by using a PEI-AQD complex with a PEI/AQD molar ratio of 300 and a nominal pDNA/PEI-AQD ratio of 6, we can achieve 75 ± 2.6% RFP expression efficiency with cell vitality remaining at 78 ± 4% of the control. (paper)

[en] Quantum dots (QDs) are semiconducting nanocrystals that have photoluminescent (PL) properties brighter than fluorescent molecules and do not photo-bleach, ideal for in vivo imaging of diseased tissues or monitoring of biological processes. Near-infrared (NIR) fluorescent light within the window of 700–1000 nm, which is separated from the major absorption peaks of hemoglobin and water, has the potential to be detected several millimeters under the surface with minimal interference from tissue autofluorescence. Here we report the synthesis and bioimaging demonstration of a new NIR QDs system, namely, CdPbS, made by an aqueous approach with 3-mercaptopropionic acid (MPA) as the capping molecule. The aqueous-synthesized, MPA-capped CdPbS QDs exhibited an NIR emission in the range of 800–950 nm with x_i ≥ 0.3, where x_i denotes the initial Pb molar fraction during the synthesis. Optimal PL performance of the CdPbS QDs occurred at x_i = 0.7, which was about 4 nm in size as determined by transmission electron microscopy, had a rock salt structure and a quantum yield of 12%. Imaging of CdPbS QDs was tested in membrane staining and transfection studies. Cells transfected with CdPbS QDs were shown to be visible underneath a slab of chicken muscle tissue of up to 0.7 mm in thickness without the use of multiple-photon microscopy. (paper)