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) measureme nts, 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 interacti ons 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 lon g-range assembly of MB on the molecular surface of nucleic acids. A Scatcha rd 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 assembl y 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 ass embly 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 b e determined if 3.0 x 14(-5) mol dm(-3) MB was employed. The limits of dete rmination 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.