In conclusion, we show that the efficiency of PEI-SWCNT module is largely affected by several biological and physical factors. The cell wall remains the first barrier where the limited size of cell wall pores impedes the passage of large-sized PEI-SWCNT-DNA composites (i.e., PEI 0.1 -SWCNT-DNA, Fig. ) where DNA is more exposed to the transcription machinery than with smaller SWCNT-DNA composites (i.e., PEI 30 -SWCNT-DNA). Thus, a sufficiently high surface potential of PEI-SWCNT is required to efficiently condense DNA and decrease the size of the composite. In addition, increasing DNA concentration often leads to precipitation of the composites due to opposite charge attraction. Furthermore, our results indicate the distribution of the positively charged PEI on the surface of SWCNT induces DNA to bind in different modes and that only composites with partially condensed DNA is expressed inside the cells. This partial condensation limits the size of the gene that can be expressed because the condensed DNA is not released from PEI30-SWCNT and thus part of the DNA sequences are unavailable to the cellular transcription machinery. Combined, this study provides an important implication that the efficient condensation of the DNA, which is a prerequisite for cell wall trafficking; and good accessibility of the transcription machinery to the condensed DNA in the cell nucleus as a prerequisite for efficient expression of the delivered gene, are hard to achieve simultaneously using the module of charge-based DNA loading onto PEI-coated SWCNTs. This trade-off may pose a challenge to utilize the PEI-SWCNT-mediated gene delivery for efficient genome engineering applications in plants, which require large multi-unit plasmid constructs. Our results strongly suggest that the development of a method enabling not only tight condensation of DNA on the carrier but also good access through the cell wall and good access of the transcription machinery to the delivered DNA would be the key for the future development of the nanomaterials-based gene-delivery to plants.