Enhanced in vitro and in vivo toxicity of poly-dispersed acid-functionalized single-wall carbon nanotubes

Abstract

Many potential applications in nanotechnology envisage the use of better-dispersed and functionalized preparations of carbon nanotubes. Single-walled carbon nanotubes (SWCNTs) were treated with 1:1 mixtures of concentrated nitric and sulfuric acids for 3 min in a microwave oven under 20 psi pressure followed by extensive dialysis to remove the acids. This treatment resulted in acid functionalized SWCNTs (AF-SWCNTs) that had high negative charge (Zeta potential −40 to −60 mV) and were well dispersed (98% of the particles <150 nm) in aqueous suspensions. In vitro and in vivo toxic effects of SWCNTs and AF-SWCNTs were compared. AF-SWCNTs exerted a strong cytotoxic effect on LA4 mouse lung epithelial cells in culture that could be blocked by prior treatment of the nanotubes with poly L-lysine which neutralized the electric charge and promoted re-agglomeration. AF-SWCNT, but not the unmodified SWCNT preparations, strongly inhibited cell cycling of LA4 cells. Both SWCNTs and AF-SWCNTS were however equally effective in inducing apoptotic responses in LA4 cells as examined using an Annexin V binding assay. Oro-pharyngeal aspiration of AF-SWCNT preparation induced a strong acute inflammatory response in the lungs of CD1 mice, compared to control SWCNTs which caused only a marginal effect. Taken together the results indicate that unlike pristine SWCNTs, acid-functionalized SWCNT preparations exert strong toxic effects in vitro and in vivo and these effects can be reversed by neutralizing their surface charge.

• Nanoparticles
• nanotubes
• particle toxicology

Acknowledgements

RKS was supported by a senior research fellowship of the National Research Council, NAS, USA. The authors are grateful to Judy Richards and Debbie Andrews for technical assistance, and Drs Aimen Farraj and Ram Ramabhadran for careful review of the manuscript. This paper has been reviewed by the National Health and Environmental Effects Research Laboratory, US Environmental Protection Agency, and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the Agency, nor does the mention of trade names or commercial products constitute endorsement or recommendation for use.