The present invention relates to the field of drug delivery, in particular the delivery of unmodified cargo molecules (such as doxorubicin and Taxol®) using iron oxide nanoparticles as therapeutic delivery agents. Specifically described are methods to entrap cargo (i.e. known therapeutics (drugs) and other types of molecules) into the exterior coating of iron oxide nanoparticles, including iron oxide nanoparticles approved for use in humans. Additionally, methods describe the use of such drug-loaded nanoparticles as therapeutic delivery agents. Further, methods include quantifying and visualizing the amount of cargo molecule loading levels when preparing these therapeutic agents and then quantifying and visualizing the amount of delivery (i.e. unloading) of these cargo molecules from these nano-particles using compact magnetic relaxometers, common NMR instruments and magnetic resonance imaging (MRI) instruments.
