Determination of nanograms of nucleic acids by their enhancement effect on the resonance light scattering of the cobalt(II)/4-[(5-chloro-2-pyridyl)azo]-1,3-diaminobenzene complex.

Using a common spectrofluorometer to measure the intensity of resonance light-scattering, a method for determination of nucleic acids in the nanogram range has been developed. In the pH range 11.5-12.0, the resonance light-scattering of the binary complex of cobalt(II)/ 4-[(5-chloro-2-pyridyl)azo]-1,3-diaminobenzene (5-Cl-PADAB) is greatly enhanced by nucleic acids, with the maximum scattering peak located at 547.0 nm. The enhanced intensity of resonance light-scattering is in proportion to the concentration of calf thymus DNA in the range 0-400 ng/mL and to that of fish sperm DNA and yeast RNA in the range 0-300 ng/mL. The limits of detection are 1.4 ng/mL for calf thymus DNA, 0.8 ng/ mL for fish sperm DNA, and 1.3 ng/mL for yeast RNA. Precision at 200 ng/mL for the three nucleic acids is 1.9%, 2.0%, and 0.8%, respectively. Six synthetic samples were determined satisfactorily. Mechanism studies showed that the nature of the reaction is that the binary complex of Co(II)/5-Cl -PADAB reacts with single-stranded nucleic acid, and the enhancement effect of nucleic acids on the resonance light scattering of the binary complex is due to the stacking of the binary complex on nucleic acids, which act as a template.