Assembly of methylene blue on nucleic acid template as studied by resonance light-scattering technique and determination of nucleic acids of nanogram

The template role of nucleic acids in the long-range assembly of Methylene Blue (MB) was characterized with Resonance Light-Scattering (RLS) measurements, and a determination method of nucleic acids of nanogram was proposed. At the pH range 6.87-8.74 and ionic strength lower than 0.01, the interactions of MB with nucleic acids result in two characteristic RLS peaks at 355.0 and 560.0 nm, Mechanism studies show that these peaks result from the long-range assembly of MB on the molecular surface of nucleic acids. A Scatchard plot was constructed by using the RLS data, yielding an assembly number and assembly constant of 5.67 and 9.22 x 10(4) mol(-1) dm(3) for MB assembly on the molecular surface of calf thymus DNA (ctDNA), 5.79 and 4.68 x 10(4) mol(-1) dm(3) for MB assembly on that of fish sperm DNA (fsDNA). This assembly could be used for analytical purposes and 0-1.4 mu g ml(-1) for ctDNA, 0-1.2 mu g ml(-1) for fsDNA, and 0-0.24 mu g ml(-1) for yeast RNA could be determined if 3.0 x 14(-5) mol dm(-3) MB was employed. The limits of determination were 11.0 ng ml(-1) for ctDNA, 4.9 ng ml(-1) for fsDNA and 8.6 ng ml(-1) for yeast RNA, respectively. Four synthetic samples were determined with satisfaction.