title: Single wall carbon nanotubes enter cells by endocytosis and not membrane penetration.
abstract: BACKGROUND
  Carbon nanotubes are increasingly being tested for use in cellular applications. Determining the mode of entry is essential to control and regulate specific interactions with cells, to understand toxicological effects of nanotubes, and to develop nanotube-based cellular technologies. We investigated cellular uptake of Pluronic copolymer-stabilized, purified ~145 nm long single wall carbon nanotubes (SWCNTs) through a series of complementary cellular, cell-mimetic, and in vitro model membrane experiments.
  
  
  RESULTS
  SWCNTs localized within fluorescently labeled endosomes, and confocal Raman spectroscopy showed a dramatic reduction in SWCNT uptake into cells at 4°C compared with 37°C. These data suggest energy-dependent endocytosis, as shown previously. We also examined the possibility for non-specific physical penetration of SWCNTs through the plasma membrane. Electrochemical impedance spectroscopy and Langmuir monolayer film balance measurements showed that Pluronic-stabilized SWCNTs associated with membranes but did not possess sufficient insertion energy to penetrate through the membrane. SWCNTs associated with vesicles made from plasma membranes but did not rupture the vesicles.
  
  
  CONCLUSIONS
  These measurements, combined, demonstrate that Pluronic-stabilized SWCNTs only enter cells via energy-dependent endocytosis, and association of SWCNTs to membrane likely increases uptake.
authors.affiliation: Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA, USA.
authors.forename: Peter N
authors.initials: PN
authors.lastname: Yaron
authors.forename: Brian D
authors.initials: BD
authors.lastname: Holt
authors.forename: Philip A
authors.initials: PA
authors.lastname: Short
authors.forename: Mathias
authors.initials: M
authors.lastname: Lösche
authors.forename: Mohammad F
authors.initials: MF
authors.lastname: Islam
authors.forename: Kris Noel
authors.initials: KN
authors.lastname: Dahl
mesh_terms: D000818:Animals; D002460:Cell Line; D058266:Dielectric Spectroscopy; D004705:Endocytosis; D011992:Endosomes / Q000378:metabolism*; D006801:Humans; D051379:Mice; D018613:Microscopy, Confocal; D037742:Nanotubes, Carbon / Q000032:analysis* / Q000737:chemistry; D020442:Poloxamer / Q000737:chemistry; D013059:Spectrum Analysis, Raman; D013696:Temperature; D013816:Thermodynamics; D053835:Unilamellar Liposomes / Q000737:chemistry
chemical_list: D037742:Nanotubes, Carbon; D053835:Unilamellar Liposomes; D020442:Poloxamer