Study of the interaction of nucleic acids with acridine red and CTMAB by a resonance light scattering technique and determination of nucleic acids at nanogram levels

Abstract

In this paper, a determinating method of nucleic acids at nanogram levels by a resonance light scattering (RLS) technique with a common spectrofluorometer has been reported. The characteristics of RLS spectra of acridine red (AR) with nucleic acids, the effective factors and the optimum conditions have been studied. In the pH range 6.40–7.10, nucleic acids and surfactant CTMAB can jointly enhance the intensity of resonance light scattering of AR and the interaction of AR with nucleic acids results in three characteristic peaks of RLS at 410, 470 and 555 nm. Mechanistic studies shows that when the molar ratio of nucleic acids to AR ( m) is smaller than 5:1, the assembly of AR on the molecular surface of nucleic acids occurs and the enhancement of RLS can be observed. The binding numbers resulting from the Scatchard plot are increased in the presence of CTMAB. When m is higher than 5:1, AR intercalates into the base pairs of DNA. The enhanced intensity of RLS is in proportion to the concentration of nucleic acids in the range 5.0×10 −8 to 8.0×10 −6 g ml −1 for yeast RNA, 5.0×10 −9 to 5.0×10 −6 g ml −1 for fish sperm DNA and 5.0×10 −8 to 1.2×10 −6 g ml −1 for calf thymus DNA. The limits of detection are 1.28, 0.095 and 8.53 ng ml −1, respectively. Synthetic samples were determined satisfactorily. Especially, the detection limit of fish sperm DNA has reached 10 −11 g ml −1. It shows that this method has high sensitivity.