ThereisageneralconsensusthatpristineCNTs,orNTswithno functional groups attached at their ends or to their surface, are toxic to cells, whereas BN NTs are considered noncytotoxic. The cytotoxicity of pristine CNTs is largely due to their insolubility in aqueous solutions, hydrophobicity, and tendency to aggregate. The cytotoxicity of NTs, however, can be reduced13 by rendering them soluble by modifying their surface chemistry.