To conduct dry-phase AFM, a few microliters of SWCNT, PEI-SWCNT or DNA-PEI-SWCNT solutions were deposited on a freshly cleaved mica surface and vacuum dried. To conduct solutionphase AFM, 10 μl of a DNA-PEI-SWCNT solution in 10 mM TE buffer was deposited on a freshly cleaved mica surface and incubated at room temperature for 5 minutes, then washed with 200 μl Milli-Q water. AFM imaging was performed in 1 mM Tris buffer (pH = 7.5) with an Agilent 5500 Scanning Probe Microscope (Agilent Technologies, CA, USA) using silicon nitride tips (AC40, Bruker) in AAC mode (tapping mode) with a scan rate of 1 Hz and an amplitude set point of 0.9 -1.2 V. Images were collected at 1 μm × 1 μm or 0.5 μm × 0.5 μm scans. To get the Liquid phase AFM images shown in Fig. , TRBO DNA-PEI 30 -SWCNT +61mV complex was suspended in the infiltration buffer. One ml of the suspension was deposited on the surface of freshly cleaved mica fixed inside a small plastic dish (Corning, NY, USA), incubated for 1 hour, then imaged using SCANASYST-FLUID+ cantilever (Bruker, USA).