Three-dimensional spectra of the long-range assembly of Nile Blue sulfate on the molecular surface of DNA and determination of DNA by light-scattering Original Research Article

The features of the three-dimensional (3-D) emission spectrum of the long range assembly of Nile Blue sulfate (NBS) on the molecular surfaces of DNAs were discussed. It was found that the emission signals involve resonance light-scattering (RLS, λRLS = λex), second order light-scattering (SLS, λSLS = 2λex), anti-second order light-scattering (ASLS, λASLS = 0.5 λex), Raman light-scattering (Raman, λRLSR = −49.0 + 1.28λex, λSLSR = −52.0 + 0.64 λex, and λASLSR = −171.7 + 2.86 λex), and fluorescence (λex = 545.0 nm, λem = 610.0 nm). The wavelengths of all light-scattering signals keep linear relationships with at of the incident light beam (λex), and the intensities of the light-scattering signals in the 3-D spectrum are in the order: IRLS > ISLS > IASLS > IRLSR > ISLSR > IASLSR. At pH 7.20–7.80 and ionic strength 0.012, these signals, including RLS, SLS, and ASLA, were found to be strongly enhanced because of the long range assembly of NBS on the molecular surface of both calf thymus DNA (ctDNA) and fish sperm DNA (fsDNA). Fluorescence quenching of NBS by DNAs occurs, but no significantly enhanced Raman light-scattering signals of NBS can be detected in the long range assembly. By independently using the enhanced intensity of RLS at 293.8 nm (λex = 293.8 nm), ASLS intensity at 293.8 nm (λex = 587.6 nm), or SLS intensity at 587.6 nm (λex = 293.8 nm), ctDNA and fsDNA at nanogram levels can be determined with identical results.