Significant spectral changes are observed in the DNA bands upon the addition of LPEI and BPEI (Figure ). For example, the 1222 cm -1 band of DNA decreases in intensity and down- shifts by ∼7 cm -1 as the N/P ratio of LPEI increases (Figure ). Additionally, although they overlap partially with the ∼1450 cm -1 band of the polymers, the nucleobase ring stretching bands between 1400 -1500 cm -1 increase in intensity as the N/P ratio increases. The 1680 cm -1 band also exhibits intensity changes, although no clear trend is observed with increasing N/P ratio.