3500 da membrane

Biocompatible SWNTs with NIR-II emission of 1100–1400 nm were prepared using a surfactant exchange method according to previous publications.^{[1 (link), 20 (link), 21 (link),48 (link)]} Briefly, raw high pressure carbon monoxide conversion SWNTs (Unidym) were suspended in a solution of 1 wt% sodium cholate by bath sonication for 1 hour. The solution was centrifuged at 300, 000 g for 1 hour to remove large bundles. The supernatant was mixed with DSPE-mPEG (1,20distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy (polyethylene glycol) 5000]) at a concentration of 1 mg/mL, and dialyzed against PBS with a 3500 Da membrane (Fisher) to remove sodium cholate. As-prepared SWNTs were centrifuged again at 3×10⁵g for 1 hour to remove aggregates. TEM imaging, as described previously,^{[35 (link)]} was performed to image the size of the quantum dots.

High-pressure carbon monoxide conversion (HiPCO) SWNTs (Unidym, Inc.) were suspended in an aqueous solution of sodium deoxycholate at a concentration of 1 wt% by bath sonication for 1 h. This SWNT suspension was ultracentrifuged at 300,000 g, the supernatant was retained and 1.0 mg·ml⁻¹ of DSPE-mPEG(5 kDa) (1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethyleneglycol, 5000)], Laysan Bio) was added. The resulting suspension was then dialyzed against 1× PBS in a 3500 Da membrane (Fisher) with pH controlled at 7.4 to remove sodium deoxycholate, leaving the SWNTs coated with the biocompatible DSPE-mPEG only.