PROBLEM TO BE SOLVED: To provide nanoparticles which can easily change the wavelength of light to respond and have excellent emission efficiency of nitric oxide. SOLUTION: A nitroso compound which is at least one selected from the group consisting of the following formula, compound (1), compound (2) and compound (3), a catalyst for oxidizing the nitroso compound under light irradiation, and the above. Nanoparticles containing the organic polymer capable of dissolving the catalyst, in which the nitroso compound and the catalyst are present in the polymer particles formed of the organic polymer. In formulas (1) to (3), R1, R2, and R3 are independently hydrogen atoms or methyl groups, and R4 is a hydrocarbon group having 1 to 10 carbon atoms. [Selection diagram] None【課題】応答する光の波長を容易に変更でき、一酸化窒素の放出効率に優れるナノ粒子を提供する。【解決手段】下式、化合物（１）、化合物（２）、化合物（３）からなる群から選ばれる少なくとも一種であるニトロソ化合物と、前記ニトロソ化合物を光の照射下で酸化する触媒と、前記触媒を溶解可能な有機ポリマーとを含み、前記有機ポリマーで形成されるポリマー粒子中に、前記ニトロソ化合物及び前記触媒が存在する、ナノ粒子。式（１）～（３）中、Ｒ１、Ｒ２、Ｒ３はそれぞれ独立に水素原子又はメチル基であり、Ｒ４は、炭素数１～１０の炭化水素基である。【選択図】なし
