Study of the interaction of nucleic acid with europium(III) and CTMAB and determination of nucleic acids at nanogram levels by the second-order scattering

This paper firstly reports the second-order scattering (SOS) phenomenon in the nucleic acid system using a common spectrofluorometer. And a novel determination method of nucleic acids at nanogram level has been developed. Studies involving calf thymus DNA (ctDNA), fish sperm DNA (fsDNA) and yeast RNA (yRNA) showed that the SOS intensity of nucleic acids can be enhanced by La3+, Ce3+, Nd3+, Sm3+, Eu3+, Gd3+ and Tb3+ ion, of which Eu3+ ion has the largest enhancement. And the intensity of the SOS is proportional to the concentration of nucleic acids. Maximum SOS peak at 550 nm appeared at pH 7.5 and 6.0 × 10−5 mol l−1 CTMAB (cetyltrimethylammonium bromide). Under the optimal conditions, the calibration graphs were linear in the range of 1.0 × 10−8 to 4.0 × 10−5 g ml−1 for ctDNA, 6.0 × 10−9 to 2.0 × 10−6 g ml−1 for fsDNA, and 8.0 × 10−9 to 1.0 × 10−6 g ml−1 for yRNA, respectively. The detection limits were 1.7 ng ml−1 for ctDNA, 0.36 ng ml−1 for fsDNA and 0.21 ng ml−1 for yRNA, respectively. In comparison with most other methods for the determination of nucleic acids, this method is more convenient, more sensitive and simpler. And the possible mechanism was proposed.