disclosed are beads , which are chemically stable even at a normal temperature , are stable without being disintegrated even if being exposed to light , can emit a plurality of fluorescence excited by irradiating a light of single wavelength , and can be identified by a flow cytometer . a method for preparing the beads , a flow cytometer and a program for preparing the beads are also disclosed . by dyeing semiconductor nanoparticles as a fluorescent reagent to polystyrene beads , beads are identified . at the same time , semiconductor nanoparticles of a different fluorescence wavelength are also used for detection of reporter , enabling snp specification of gene , monitoring or finding of the concentration of biopolymer such as a protein . the semiconductor nanoparticles have a feature that the fluorescence wavelength may vary by controlling the particle size and that they have a high durability compared to an ordinary fluorescent reagent since they are a semiconductor .