Aggregation of carbon nanotubes can increase toxicity Conversely, all PEI-SWCNT were prone to fast aggregation where the hydrodynamic diameter measurements showed an increase of tenfold (from 15 nm to 150 nm) when stored at room temperature for 24 hours (Fig. ). However, these aggregates were shown to transiently disperse when the solution was briefly probe-tip sonicated for 5 minutes (Fig. ). See Supporting Text 4 for a detailed discussion on the physical differences between PEI-SWCNT and chitosan-SWCNT, their role in the organization of the ion layers around the composites, and how these differences affect the dynamic light scattering data and DNA loading.