Similarly, the sequential addition of salts did not release the DNA from the PEI 30 -SWCNT +61mV -DNA complex (Fig. ). These results confirm that DNA is strongly held to the surface of the PEI 30 -SWCNT +61mV irrespective of its binding mode and suggest that the complex undergoes no physical changes under conditions of high pH or high salt concentration, including physiological pH and ionic strength.