A new structured metallic nanomaterial of europium nanoparticle was prepared using tannic acid as the reductive agent, and nanoeuropium protein conjugates were synthesized by the method of lipoic acid modification on the surface of nanoparticle, which opens a new field of application of lanthanides in nanotechniques. Their properties were also characterized by UV–vis absorption spectroscopy, transmission electron microscopy (TEM), and fluorescence spectroscopy. The europium nanoparticle and its protein conjugates solution were stable and water-soluble. The fluorescence intensity of the composite europium nanoparticles was significantly increased in the presence of trace protein, and was linear proportional to the concentration of proteins under optimum conditions. According to this, a fluorimetric method for the determination of protein was developed in this paper.
