3D distribution and localization of QDs in MSCs and cardiac myocytes. A cut view through 12 (a) and16 (b) superimposed optical sections illustrating the 3D distribution of QDs in MSC and Cardiac Myocyte cultures 24 hrs post QD labeling. The sections shown are taken from the intracellular space of the cells indicated by the blue arrows with the red (vertical) and green (horizontal) crosshairs aligned near QD aggregates. a. The QDs are homogeneously distributed through the MSC cytosol, have not formed large aggregates and are clearly visualized in the intracellular space as indicated by the red arrow. Scale bar = 20 μm. b. 3D distribution of QDs in the cardiomyocyte culture clearly show QDs located on the cell surface as indicated by the red arrow. No QD uptake was observed in the cytosol of the cardiac myocyte. Scale bar = 20 μm.