DETERMINATION OF DNA AND RNA BY THEIR QUENCHING EFFECT ON THE FLUORESCENCE OF THE TB3-TIRON COMPLEX()

The fluorescence quenching of the Tb3+-Tiron complex by nucleic acids is reported. Studies involving calf thymus(CT) DNA, salmon(SM) DNA, he rring sperm(HS) DNA and yeast RNA revealed that they compete with Tiro n for the Tb3+ ion, which resulted in the fluorescence quenching of th e Tb3+-Tiron complex because the Tb3+-nucleic acid complex is non-fluo rescent under the same conditions. The ratio of molar concentrations o f Tb3+ and Tiron appeared to be a key factor, a Tb3+:Tiron ratio of 3: 10 being the most suitable. The maximum fluorescence was produced at p H 6.9, with maximum excitation and emission wavelengths at 317 and 546 nm, respectively. Under optimal conditions, the differential value of fluorescence intensity in the absence and presence of nucleic acids w as proportional to the concentration of nucleic acids over the range o f 0.005-1.0 mu g ml(-1) for CT DNA, SM DNA, HS DNA, and 0.005-0.7 mu g ml(-1) yeast RNA. The detection limits were 1 ng ml(-1) for CT DNA, 1 ng ml(-1) for SM DNA, 0.9 ng ml(-1) for HS DNA, and 0.6 ng ml(-1) for yeast RNA, respectively. The relative standard deviations (6 replicat es) were within 2.5% in the middle of the linear range. The mechanism for the fluorescence quenching was also studied. (C) 1997 Elsevier Sci ence B.V.