A caged platinum nanocluster complex is disclosed. The complex comprises (a) an amine-terminated dendrimer; and (b) a platinum nanocluster comprising platinum oxides, the platinum nanocluster being confined inside of the amine-terminated dendrimer. The complex exhibits cytotoxicity to cancer cells. A double-caged platinum nanocluster complex is also disclosed, which comprises polyethylene glycol (PEG) coated on the surface of a dendrimer caged platinum nanocluster complex. The double-caged caged platinum nanocluster complex comprises pH-sensitive bonds on the surface thereof. Also disclosed are methods of preparing and using the same.