The present invention provides functionalized magnetic nanoparticles comprising a functional group, which functionalized magnetic nanoparticles exhibit differential binding to a tissue, indulging brain tissue, bone, and vascular tissues. The present invention further provides compositions, including pharmaceutical compostions, comprising a subject functionalized magnetic nanoparticle. The present invention further provides diagnostic and research methods including use of subject functionized magnetic nanoparticles. The present invention further provides a magnetic resonance imaging (MRI)-visible drug delivery system drugs using MRI, as well as tissue-specific drug delivery.