Confocal fluorescent and electron microscopy of CD34⁺ cells. Human CD34⁺ cells exposed to 10 μL/mL of the iron oxide fluorescent particles for 18 hours, washed, and analyzed. (A) Depicted are phase contrast images of the CD34⁺ cells (i) and the green fluorescence of the cells (ii). Panel Aiii shows an overlay of panels Ai and Aii. Also shown is green fluorescence from the iron oxide particles within the cell (iv) and Cell Tracker Orange fluorescence of the cytoplasm of viable cells (v). Panel Avi shows an overlay of panels Aiv and Av, demonstrating a granular distribution of the particle fluorescence throughout the cytoplasm of the cell. Original magnification for Ai-Avi, × 400. (B) Electron micrograph of single CD34⁺ cell showing accumulation of iron particles into membrane-bound organelles (arrows indicate examples). Original magnification, × 400.