This paper describes the synthesis of an aqueous colloidal solution of Eu(OH)3 nanoparticles stabilized by polyvinylalcohol or polyvinylpyrolidone prepared in a sonication bath. These nanoparticles were used as nanolabeling agents for living sperm cells. The nanoparticles retain their desirable optical properties, which are typical of europium inside the sperm cell. The nanoparticles did not affect the sperm cell motility or the sperm's ability to undergo an acrosome reaction. Furthermore, this work demonstrates for the first time the localization and the quantification of the loaded nanoparticles in the subcellular fractions, cytosol, plasma membrane, nucleus, and cytoskeleton, using ICP measurements.