The present invention has an object to provide a novel cerium oxide nanoparticle and to find novel uses of this cerium oxide nanoparticle. The present invention provides: a cerium oxide nanoparticle whose surface is covered with a vinyl polymer having a heterocyclic amine skeleton such as piperazine, pyridine, imidazole, or carbazole or with a polyamide having a heterocyclic amine skeleton such as piperazine, pyridine, imidazole, or carbazole; and a decomposition method of a nucleic acid or a polypeptide by using the cerium oxide nanoparticle.
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