Structure of the fluorescent compound (enhancer-Eu-VSOP). The Eu3+ ions located on the surface of the iron core of Eu-VSOP are coordinated by the enhancer components. The HEE is prepared based on the antenna system formed by the chelator (β-NTA) and the ligand (TOPO) with a modified buffer system. This complex is surrounded by Triton X-100 forming a micelle. The suggested structure is based on the structure of commercial enhancers for fluorescence detection of Eu in analytical procedures as suggested by Hemmilä et al.