Radioactive nanoparticles and methods of making and using the same

A method of performing brachytherapy, the method comprising:

• disposing a composition within a biological compartment,
• wherein the composition comprises a plurality of radioactive nanoparticles, at least one of the plurality of radioactive nanoparticles comprising:
• a metal nanoparticle core;
• an outer metal shell disposed over the metal nanoparticle core;
• a metallic radioisotope disposed within the metal nanoparticle core or within the outer metal shell;
• and
• an inner metal shell disposed between the metal nanoparticle core and the outer metal shell,
• wherein the radioactive nanoparticle has a size of about 30-500 nm in three dimensions,
• wherein the metal nanoparticle core is formed from Au, the inner metal shell is formed from Cu, and the outer metal shell is formed from Pd, Rh, or Au, and
• wherein radiation emitted by the metallic radioisotope passes through the inner metal shell and/or the outer metal shell into a surrounding environment of the nanoparticle without heating the inner metal shell and/or the outer metal shell.