Representative confocal microscope images depicting subcellular localizations of green CdSe/ZnS-COOH QDs after 24 h treatment with QDs in HeLa cell culture. (A, top) Colocalization of the early endosome reference marker Rab5a-TagRFP with the QDs in the presence of serum. (A, bottom) Partial colocalization of QDs with Rab5a-TagRFP in cells grown in the medium lacking serum. The arrow indicates a spatial area of no colocalization between QDs and Rab5a-TagRFP. (B, top) Colocalization of the late endosome reference marker Rab7a-TagRFP with the QDs in the presence of serum. (B, bottom) Colocalization of QDs with Rab7a-TagRFP in cells grown in the medium lacking serum. (C, top) Colocalization of the lysosome reference marker LysoView 540 with the QDs in the presence of serum. (C, bottom) Colocalization of QDs with LysoView 540 in cells grown in the medium lacking serum. Scale bars correspond to 10 µm.