Nephelometric determination of micro amounts of nucleic acids with protamine sulfate

Nucleic acids can form large particle complexes with protamine sulfate by electrostatic forces, which results in strong light scattering. Based on this, a nephelometric method is described for sensitive and convenient determination of nucleic acids with protamine sulfate by using a common spectrofluorimeter. Maximum light scattering is produced in the range of pH 2.2-4.4 with the same excitation and emission wavelengths at 365 nm. Under optimal conditions, the calibration curves are linear in the range 0.05-60.0 micrograms cm-3 for nucleic acids. The corresponding detection limits are 12.5 ng cm-3 for calf thymus DNA, 9.0 ng cm-3 for fish sperm DNA, and 18.0 ng cm-3 for yeast RNA, respectively. Six synthetic samples are determined with satisfactory results. The relative standard deviation of five replicate measurements is 3.2% for 2.0 micrograms cm-3 calf thymus DNA.