Rat mesenchymal stem cells, extracted from bone marrow, and labelled with Iron Oxide nanoparticles, before re-implantation. The image shows a section of the brain, stained with Eosin (pink) and then Prussian blue (blue/purple).
Prussian blue is a common histology stain; used to detect the presence of iron. The stain uses solutions of potassium ferrocyanide and hydrochloric acid to stain tissue. Iron deposits are then stained as blue or purple.