Confocal fluorescent microscopy of porcine mesenchymal stem cells. A subconfluent monolayer of primary porcine marrow MSCs were exposed to 10 μL/mL of the iron oxide fluorescent microparticles overnight. Excess particles were washed off with PBS. (A) Green fluorescence of beads. (B) Red fluorescence of endosomal marker CM-DiI. (C) Colocalization of the 2 colors confirming endosomal particle uptake. (D) Nomarski optics view revealing the outlines of the fibroblastic cells and the iron particles clearly clustered in perinuclear organelles. Original magnification for all panels, × 100.