An object of the present invention is to increase the dye content in nanoparticles and to improve the signal intensity per particle. According to the nanoparticle including at least a silicon naphthalocyanine or a derivative thereof and a surfactant, wherein the proportion of the silicon naphthalocyanine or the derivative thereof is 70% or more by weight in relation to the other component of the particle exclusive of the surfactant, the dye content in the nanoparticles can be increased and the signal intensity per particle can be improved without weakening the signal intensity per dye molecule (light absorptivity)
