Solutions of SWCNTs, PEI-SWCNTs, and DNA-PEI-SWCNTs were diluted to a final concentration of 7 µg ml -1 . QELS and zeta potential data were acquired using Malvern Zetasizer Nano ZS (Malvern, Worcestershire, United Kingdom). The system was equipped with a HeNe laser (633 nm) and was capable of measuring the size of particles of 0.3 nm to 10 µm. Data were analyzed using Zetasizer (Malvern) and OriginPro (Originlabs) software. The polydispersity index of the original QELS distributions was calculated using Zetasizer software.