Fluorescent approach for visually observing quantum dot uptake in living organisms

This study examines the in vivo uptake and internalization of fluorescent quantum dots (QDs) in Escherichia coli and Caenorhabditis elegans models. E. coli cells were directly exposed to QDs of different concentrations (up to 20 nM), and the uptake or sorption of QDs was monitored by flow cytometry. We observed a concentration-dependent increase in QD fluorescence with no changes in the forward or side scatter for any QD concentration, likely because the QDs are very small. Furthermore, QD uptake/adsorption did not significantly affect E. coli viability assessed by colony formation and size. QD-exposed E. coli were then fed to C. elegans to monitor the localization and effects of QDs. In our study, QDs had no observable effect on the viability or reproduction of C. elegans. We visualized QD incorporation and biodistribution by using confocal laser scanning microscopy (CLSM) with z-stacks, lambda scanning, and linear unmixing techniques, which allowed us to observe QDs in vivo and deconvolute QD fluorescence from autofluorescence. CLSM z-stacks with 10-mu m depth revealed that the QDs exclusively localized to the gut and intestine with no transfer to other tissues. The combination of these techniques for in vivo imaging of QDs and other fluorescent nanoparticles will be a powerful tool for future studies examining the uptake and biodistribution of nanoparticles. (C) 2015 Elsevier Ltd. All rights reserved.