Determination of nucleic acids at nanogram levels with safranine T by a resonance light-scattering technique Original Research Article

This is the first report of the determination of nucleic acids based on their template roles for long range assembly of organic dyes. At pH 7.05 and ionic strength 0.0045, the interactions of safranine T (ST) with nucleic acids result in three characteristic peaks of resonance light scattering (RLS) at 328.0, 472.0 and 572.0 nm. Mechanistic studies show that these peaks result from the long range assembly of ST on the molecular surface of nucleic acids. A Scatchard plot has been constructed at first with the data obtained by using the RLS technique. The binding number and intrinsic binding constant resulting from the Scatchard plot are 4.2 and 1.25×105 l mol−1 for the assembly of ST on the molecular surface of calf thymus DNA. The same parameters are 4.3 and 2.40×105 l mol−1 for the assembly on that of fish sperm DNA, 2.9 and 2.41×105 l mol−1 on that of yeast RNA. If 4.0×10−5 mol l−1 of ST was employed, linear relationships were found between the enhanced intensity of RLS at 328.0 nm and the concentration of nucleic acids in the range 0–2.5 μg ml−1 for calf thymus DNA, and 0–3.0 μg ml−1 for fish sperm DNA and yeast RNA. The limits of determination were 13.2 ng ml−1 for calf thymus DNA, 39.8 ng ml−1 for fish sperm DNA and 61.1 ng ml−1 for yeast RNA. Six synthetic samples were determined satisfactorily.