Effects of QDs on ES cell viability, proliferation, and differentiation. (A) Trypan blue exclusion assay and (B) CyQuant cell proliferation assay both showed no significant difference between unlabeled ES cells and labeled ES cell at 24, 48, and 72 hours. (C) RT-PCR analysis showed the levels of endoderm (AFP), mesoderm (Flk-1), and ectoderm (Ncam) germ layer marker increased from day 0 to day 14 of spontaneous ES cell differentiation using the hanging drop assay. The stem cell marker Oct4 decreased during the same period as expected. GAPDH is a loading control for all cells. Both QD labeled and unlabeled ES cells showed similar pattern on RT-PCR analysis.