1. The peptide and DNA were dissolved separately in 10 mM Hepes buffer (pH 7.3).
2. A two-fold excess volume of peptide solutions of various concentrations was added to the DNA solution to form peptide/pDNA complexes with different compositions.
3. The final DNA concentration was adjusted to 30 μg/mL, and complex solutions were stored at room temperature for 15 min before use.
4. The N/P ratio (2, 4, or 8) was defined as the residual molar ratio of the amino and guanidino groups of amino acids in the peptides to the phosphate groups of DNA.
5. The fluorescence intensities of peptide/pDNA solutions prepared at various N/P ratios were measured using a spectrofluorometer (ND-3300).