DNA precipitation was monitored by UV-Vis measurements using a Thermo Evolution 201 UV-Vis spectrophotometer. Polycation were incubated with 100 µg calf thymus DNA solution in 10 mM Tris-Cl buffer (pH 7.5) at increasing cationic amine (N) to anionic nucleic acid phosphate (P) ratio. After achieving the desired nitrogen-to-phosphate (N/P) charge ratio, all samples were diluted to a final volume of 300 µL with buffer, incubated for 10 min at room temperature then centrifuged at 11000 x g for 15 minutes before measurement. Then 250 µL of supernatant solution was placed in a 1 mm pathlength cuvette. UV-Vis spectra was obtained in the range of 200-400 nm. DNA precipitation was followed by measuring the change in absorbance of the supernatant at 260 nm as a function of N/P charge ratio of the resulting polyplexes.