We showed that the binding mode of DNA to PEI-SWCNT is a key factor that governs the successful expression of GFP. However, this does not explain the failure of DNA expression of large functional DNA units on the multiple plasmids used in our experiments. Our AFM results (Fig. , Fig. ) suggest that the GFP expression is likely to originate from the uncondensed parts of partially condensed DNA (free and thus available to the cellular transcription machinery (Fig. , Fig. )) but not from the extended or condensed parts (strongly bound to the PEI-SWCNTs and thus unavailable to the cellular transcription machinery (DNA-1 and DNA-2 in Fig. )).