Our AFM measurements, and transformation results (Fig. , 5, Figs. S12, S13, S14, S15, and Supporting Appendix 1, 2) suggest a strong correlation between the Zeta potential values, mode of plasmid DNA binding to the surface of PEI-SWCNTs, and the efficiency and reproducibility of transformation. Because the binding of plasmid DNA neutralized the local charge of PEI-SWCNTs, we were not able to assign a specific mode of binding to a specific range of local surface potentials (Supporting Text 6). However, the partially-condensed and condensed DNA were observed exclusively in the PEI-SWCNT composites of high zeta potentials (ζ = 61-77 mV); meanwhile, a non-uniform height and surface potential distribution exists along the surface of individual PEI-SWCNTs. Thus, we posit that the condensed and partially condensed DNA binding modes are linked to zones of PEI-SWCNTs with higher positive surface charge, whereas the extended DNA binding mode is linked to zones of PEI-SWCNTs with moderate positive surface charge. Although the partially condensed DNA is much smaller in size than the free plasmid DNA (Fig. ), our observations indicate that the partially condensed DNA shows extrusions that allow for the expression of DNA in the plant cell (Fig. , Fig. ). The negative expression results observed for PEI 0.1 -SWCNT +30mV could be due to the inability of the larger DNA-PEI-SWCNT complex (i.e., ~200 nm physical size of the bound DNA, Fig. ) to get through the plant cell wall pores.