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The accumulation of nontargeted quantum dots in cultured human embryonic kidney cells

Quantum dots (QDs) could offer significant advantages in clinical settings due to their high photostability and quantum yield. We are investigating the uptake and compartmentalization of QDs by cells because these processes are not fully characterized and there is potential for heavy metal toxicity when semiconductor nanocrystals are sequestered. Here we demonstrate the intracellular accumulation of QDs in human embryonic kidney cells (HEK-293; ATCC) exposed to nontargeted (Qtracker 565nm; QDot Corp.) or targeted (Qtracker 565 Cell Labeling Kit; QDot Corp.) QDs. As expected, 10 nM targeted QDs (Lagerholm et al., 2004, Nano Letters, 4:2019-2022) accumulated in HEK-293 cells and normal human astrocytes (NHA; Cambrex Biosciences) after 1 hr, while nontargeted QDs (200 nM) could be detected after 24 hr in HEK-293 but not NHA. The uptake of 10 nM targeted QDs was greater than the uptake of 200 nM nontargeted QDs as confirmed by the number and intensity of puncta visible in HEK-293 cells imaged with confocal microscopy. QD uptake was not detected in two Xenopus kidney cell lines (XLK-WG and A6; ATCC) exposed to nontargeted QDs (10-500 nM) for 18 hours. Co-labeling of HEK-293 cultures with CellTracker Red CMTPX (Invitrogen) following QD uptake verified that QD accumulation does not affect cell viability. Differences in QD uptake between cell lines could be species-specific or due to different growth conditions. The unexpected accumulation of nontargeted QDs raises questions about the uptake mechanism and the intracellular location that are being investigated with TEM. Supported by NIH-NIDCD (DC003292) and NMSU-ADVANCE (NSF0123690) to EES.