In one aspect, radioactive nanoparticles are described herein. In some embodiments, a radioactive nanoparticle described herein comprises a metal nanoparticle core, an outer metal shell disposed over the metal nanoparticle core, and a metallic radioisotope disposed within the metal nanoparticle core or within the outer metal shell. In some cases, the radioactive nanoparticle has a size of about 30-500 nm in three dimensions. In addition, in some embodiments, the radioactive nanoparticle further comprises an inner metal shell disposed between the metal nanoparticle core and the outer metal shell. The metal nanoparticle core, outer metal shell, and inner metal shell of the radioactive nanoparticle can have various metallic compositions.
