Described herein are methods of delivering a nanoparticle to the brain of a subject by administering to the subject a nanoparticle having a nanoparticle core and a targeting agent. A variety of targeting agents may serve to promote delivery of the described nanoparticle. For example, the targeting agent may include a ligand specific for a receptor expressed by brain endothelial cells and a linker that connects the ligand to the external surface of the nanoparticle core. Additionally, the linker can promote disassociation of the ligand from the nanoparticle when inside a cell.