The negatively charged control siRNA molecule migrated through the agarose gel, giving a distinct band visible in the first lane (1) (Figure ). Pure siRNA was completely degraded in the presence of RNase A (lane 2). Both molar ratios established by zeta potential titration measurements were selected for the experiment. At both molar ratios for both dendrimers, an siRNA signal was observed in the third (3) and seventh (7) lanes because the positively charged dendrimers did not form sufficiently stable complexes with the siRNA to survive the voltage applied to the gel. When siRNA was incubated with dendrimers, treatment with RNase caused siRNA degradation in both dendriplexes (lanes 4 and 8). This may be due to the conformation of the complex formed by the analyzed dendrimers and siRNAs (e.g. by its open structure), leading to siRNA degradation as the entire complex is not tight enough to prevent RNAse from entering it. The addition of heparin was intended to show the release of the entire siRNA pool from the complexes, as indicated by an intensity band comparable to the positive control for siRNA (lanes 5 and 9). When heparin was added to RNAse treated dendriplexes, no siRNA remained in the well, indicating no undegraded nucleic acid (lanes 6 and 10). Importantly, lowering the pH from 7.7 to 5 did not degrade the siRNA and did not inhibit its release from the complex (lanes 11 and 12).