TABLE 1.

Troubleshooting table.

Step	Problem	Possible reason	Solution
2	SWNTs are not well suspended by PL-PEG	Sonication is not efficient because of inappropriate vial position in the sonicator	Adjust the position and angle of the vial in the sonicator. Ensure the water bath is at the recommended level
5	Nanotubes are very sticky on the filter device during filtration	A certain amount of stickiness is normal for PL-PEG2000-Amine functionalization but not for PL-PEG5000-Amine. This may be due to poor coating of PL-PEG molecules on nanotubes.
		The PL-PEG/SWNT ratio is not sufficient when making nanotube suspensions.	Reduce the amount of SWNTs or increase PL-PEG concentration during sonication
		Water in bath is too hot during sonication	Change water in the water bath sonicator more frequently during sonication
6C (vii)	The radiolabeling yield is very low (e.g., <30%)	This may be due to metal ion contamination in the SWNT solution	Dialyze the SWNT solution against deionized distilled water with a 10-kDa MWCO membrane for 2 d before radiolabeling
6D (ix)	Cells are contaminated by bacteria after 3 d incubation	SWNT solution is not well sterilized before adding into the cell culture	Normally centrifuging SWNT-siRNA solution for 10 min at 10,000g will resolve this problem. Repeating the centrifuge step 2–3 times will be helpful. Carefully take out supernatant and discard any aggregates after centrifugation. Use sterilized containers during experiments
6E(ii)	A large amount of SWNT–DOX complex precipitates during centrifugation	The DOX loading on nanotubes is too high in this case. This stability issue is more frequent when making SWNT–RGD–DOX	Reduce pH in the loading solution to 7.8–8.0 by adding less sodium bicarbonate buffer Add 10–20 μM of PL-PEG into the loading solution. This will increase the stability of SWNT–RGD–DOX and not affect DOX loading and RGD targeting