Enhanced fluorescence of the Eu3+–naphthalenediimide derivative–phenanthroline ternary complex and the determination of DNA

The naphthalenediimide derivative carrying a single bis((beta)-diketone)-o-terphenyl moiety (NDI–BHHCT) and its chelates formed with europium(III) were studied using absorption and fluorescence spectroscopy. The effect of solvent on the spectral properties and solubility of the system was investigated. Enhancement of the europium fluorescence as a function of 1,10-phenanthroline (phen) and yttrium(III) ions was examined in the presence and in the absence of DNA. On the basis of these studies, a system Eu3+/Y3+/NDI–BHHCT/phen was applied for the determination of calf thymus DNA. In the presence of DNA, the Eu3+ and Y3+ ternary complexes intercalate to DNA that results in their proper arrangement on the DNA helix, thus enabling energy transfer between the non-fluorescent Y3+ and fluorescent Eu3+ chelates. As the result, the enhancement of Eu emission due to the co-fluorescence effect is observed in the presence of DNA. The calibration graph was linear up to 1.3 (mu)g ml^-1 with a detection limit of 12 ng ml^-1.