Disclosed are photoluminescent particles. The particles include a core nano-sized particle of carbon and a passivation agent bound to the surface of the nanoparticle. The passivation agent can be, for instance, a polymeric material. The passivation agent can also be derivatized for particular applications. For example, the photoluminescent carbon nanoparticles can be derivatized to recognize and bind to a target material, for instance a biologically active material, a pollutant, or a surface receptor on a tissue or cell surface, such as in a tagging or staining protocol.