Study on the dimer–monomer equilibrium of a fluorescent dye and its application in nucleic acids determination

A novel spectrofluorimetric method has been proposed for the determination of nucleic acids based on shifting the dimer–monomer equilibrium of the fluorescent dye, acridine yellow (AY). Induced by the premicellar aggregation of an anionic surfactant, sodium dodecyl sulphate (SDS), AY formed a nonfluorescent homodimer (AYAY) which largely quenches the fluorescence intensity of the dimer system. However, the fluorescence intensity of the system increased dramatically when nucleic acids were added to the solution. The fluorescence enhancement is probably based on the DNA modulated shift of the dimer–monomer equilibrium of AY in the anionic surfactant solution. Intercalation of the monomer in DNA caused the dissociation of AYAY, and led a very high fluorescence enhancement. A linear dependence of fluorescence intensity on Calf thymus (CT) DNA concentration over the rang of 0∼40 μg/ml CT DNA allowed sensitive quantification of CT DNA by a simple fluorescent method. The detection limit was 0.023 μg/ml and the RSD was 1.5% for 2 μg/ml CT DNA (n=7). Furthermore, calibration graphs for yeast RNA, polynucleotides, such as poly (A) and poly (I) were also obtained.