Following electrophysical characterization, which suggested that SWCNT surface charge plays an important role in the binding mode of DNA and its resulting accessibility for expression and transformation, we investigated whether physical factors and charges in solution could play a role in enhancing gene expression. We investigated the inherent variability in the DNA-PEI-SWCNT complex infiltrated into N. benthamiana leaves. To that end, multiple preparations of PEI 30 -SWCNT were conjugated with TRBO-G plasmid DNA and infiltrated into N. benthamiana plant leaves. The different PEI-SWCNT preparations showed diverse expression results, with 2 of the 19 conditions tested yielding consistent expression, as summarized in Table . Next, to confirm whether the infiltration buffer composition limited plasmid delivery and transgene expression in plant cells, PEI 30 -SWCNT +61mV was mixed with the DNA plasmid in water as a solvent (ζ = +61 mV, Fig. ), half-strength MES buffer (MES 12.5 mM and MgCl 2 7.5 mM, pH 6, ζ = +51 mV, Fig. ), and full-strength MES buffer (MES 25 mM and MgCl 2 15 mM, pH 6, ζ = +41 mV, Fig. ) and infiltrated into N. benthamiana leaves. We note that these zeta potential values were measured at different salt concentrations without DNA. In our experiments, we added the buffer and DNA simultaneously to the water solution of PEI-SWCNTs (ζ = +61 mV). The DNA-PEI 30 -SWCNT complex infiltrated in the half-strength MES buffer consistently exhibited higher GFP expression than the full-strength MES buffer and water only used as infiltration buffer (Fig. ). Almost all leaf slices showed the GFP signal when the half-strength MES buffer was used whereas only a limited area exhibited the GFP signal when full-strength MES buffer was used (Fig. ).