PEI-SWCNTs were prepared following the procedures described by Demirer et al. All chemicals and equipment of the exact catalog numbers mentioned in the Demirer et al. protocol were used in the preparation of PEI-SWCNTs. Briefly, 30 mg of carboxylated SWCNTs (COOH-SWCNTs) were added to 30 ml nuclease-free water and bath sonicated for 10 minutes, and then tip sonicated (6 mm probe 10% amplitude) for 30 min on ice. COOH-SWCNTs were centrifuged for 1 h at 18,000 rpm and the supernatant was collected. COOH-SWCNTs (2 mg) were reacted with 10 mg of 1-ethyl-3-[3-dimethylaminopropyl] carbodiimide hydrochloride (EDC) and 10 mg of N-hydroxysuccinimide (NHS) in 100 mM MES buffer (pH 4.5-5). After bath sonication for 10 minutes, the reaction was continued for 1 h on an orbital shaker at 180 rpm. Excess NHS and EDC were removed and MES buffer was replaced with 0.1 PBS pH 7.4 by washing the samples on a 100 kDa filter three times. The EDC-and NHS-reacted COOH-SWCNTs were reacted with 0.1, 20, 30, 40, 60 mg of PEI (25,000 MW, branched). The reaction was continued for 12 h on an orbital shaker at 180 rpm. PEI-SWCNT samples were washed with nuclease-free water 7 times on a 100 kDa filter. PEI-SWCNTs were bath sonicated for 15 minutes and then probe sonicated for 15 minutes on ice. The PEI-SWCNTs were then centrifuged for 1 h at 16,000 rpm and the supernatant was collected. Zeta potential measurement was used to judge the quality of the synthesis (see Supporting Text 5). We note that were able to obtain reproducible results by using PEI 30 -SWCNT but not by using PEI 20 -SWCNT. The latter consistently showed zeta potential value <+60mV at normal incubation conditions and inconsistently showed zeta potential value of ~+60mV by increasing the incubation time to 18 h. Thus, we presented and discussed the results of the working PEI-SWCNT composite (PEI 30 -SWCNT). All chemicals and equipment used in this study are listed in Supplementary information.