ZnO nanoparticles have been used for many applications, including in cell labeling application. Its light emission can be used to determine and identify biology cells. Wet chemical precipitation method has been successfully done to synthesize the nanoparticle and it was subsequently continued by encapsulating with silica to keep ZnO stabilized in water to be properly used in cell labeling application. Varying precipitation temperatures has been performed to control the nanoparticle size and the addition of F127 surface active agent was carried out to prevent the agglomeration. The results showed the smallest nanoparticle (3.49 nm) was obtained from the process with temperature of 25oC, with the highest band gap energy, 3.12 eV. On the other hand, the largest nanoparticle (13.16 nm) was obtained from synthesis at temperature of 65oC, with the lowest band gap energy, 3.08 eV. These levels of band gap energy are potentially suitable for cell labeling application.