To establish that PEI-SWCNTs can be used for DNA plasmid delivery into plant cells, PEI-SWCNT and chitosan-SWCNT conjugates were prepared through amide bond formation between the positively charged polymers PEI (branched, MW 25,000) or chitosan and the carboxylate groups of SWCNTs following the protocols published by Demirer et al. and Kwak et al. Six SWCNT conjugates were made using chitosan (5 mg) and different ratios of PEI (0.1, 20, 30, 40, and 60 mg) with 1 mg of SWCNTs for each (Fig. shows AFM images of PEI 30 complexed with DNA in 3:1). All the PEI-SWCNTs were washed multiple times, and the complete removal of free PEI from the solution was confirmed with agarose gel electrophoresis (Fig. ). Next, the 4.2-kb plasmid harboring a GFP cassette was conjugated with PEI 0.1 -SWCNT, PEI 30 -SWCNT, PEI 40 -SWCNT, and PEI 60 -SWCNT and infiltrated into N. benthamiana leaves. Since a previous study demonstrated negative nuclear expression of genes when plasmids were conjugated to chitosan-SWCNTs, we used this complex as a negative control. Confocal microscopy of the PEI-SWCNT-DNA infiltrated leaves confirmed the expression of mGFP from the 4.2-kb plasmid. A very weak GFP fluorescence was detected in sporadic patches close to the infiltration sites when the leaves were infiltrated with PEI 30 -SWCNT-DNA, but not with chitosan-SWCNT-DNA (Fig. ). The same conjugates were injected into cotyledonary leaves of cotton (Gossypium hirsutum) seedlings. Similar to N. benthamiana, confocal microscopy confirmed very low levels of GFP expression in cotton cotyledonary leaves (Fig. ). Next, quantitative reverse transcription PCR (RT-qPCR) was performed to confirm the expression of GFP. A low level of the GFP expression was detected in N. benthamiana samples infiltrated with PEI 30 -SWCNT-mGFP (4.2-kb), but not with chitosan-SWCNT-mGFP (4.2-kb) negative control (Fig. ).