Fluorescence reaction of terbium(III) with nucleic acids in the presence of phenanthroline

The fluorescence enhancement reaction of terbium(III) with DNA or RNA in the presence and absence of phenanthroline (Phen) was studied. Studies involving natural and denatured calf thymus DNA, fish sperm DNA and yeast RNA revealed that the presence of phen enhanced the net fluorescence 3–12-fold. The results suggest a 1 : 2 molar ratio of terbium(III) and phen for the ternary complex. Maximum fluorescence was produced in the pH range 6.8–7.2. The calibration graphs was linear between 0.4 and 15.0 or 20.0 μg ml −1 for thermally denatured nucleic acids and the detection limits were 0.1–0.2 μg ml −1. The relative standard deviation (six replicates) was within 3.0% in the linear range. Yeast RNA could be determined in the presence of up to 40% calf thymus DNA and the latter was determined when the content of yeast RNA in synthetic samples was below 10%.