Because the binding of DNA to PEI 30 -SWCNT +61mV is charge-dependent, an increased change in pH or high salt concentration could favor surface charge neutralization and the subsequent release of DNA. To that end, PCR was performed in Tris buffer (pH = 9). Similar to previous results, PCR did not amplify the respective DNA fragment compared to the proper amplification from the control vectors with two different primer sets (Fig. ). Similarly, we found that increasing the salt concentration up to 1 M NaCl, an order of magnitude higher than the physiological ionic strength, did not release the condensed DNA from the PEI 30 -SWCNT +61mV . Next, the DNA-PEI 30 -SWCNT +61mV conjugation was carried out in the presence of different salts. Gel electrophoresis results confirmed no release of the DNA from the DNA-PEI 30 -SWCNT +61mV complex (Fig. ).