Abstract
A clear understanding of nanoparticle interactions with living systems at the cellular level is necessary for developing nanoparticle-based therapeutics. Magnetic iron oxide nanoparticles provide unique opportunities to study these interactions because of their responsiveness to magnetic fields. This enables sorting of cells containing nanoparticles from in vivo models. Once sorted, flow cytometry can identify individual cell types, which can be further analyzed for iron content, gene or protein expression changes associated with nanoparticle uptake, and for other biological responses at a molecular level. Here we provide a detailed protocol to sort and identify cells in the tumor microenvironment that have internalized magnetic iron oxide nanoparticles following intravenous administration.