The differences in LPEI and BPEI morphologies suggest molecular-level differences in their binding and packaging mechanisms to DNA. To further investigate these differences, we first studied the kinetics of polyplex formation and the binding affinity of LPEI and BPEI polymers to DNA using UV absorbance spectroscopy. The kinetics of polyplex formation at N/P ratios of 1 and 5 were followed by monitoring the apparent absorbance changes in the DNA at 260 nm (Figure ), corresponding to the π → π * transition of the nucleobases. As shown in Figure , DNA absorbance at 260 nm decreases over time in the presence of both LPEI and BPEI, indicating DNA condensation due to complexation with these polymers .