The cytotoxicities of single-walled carbon nanotubes （SWNTs） and acid purified single-walled carbon nanotubes （SWNT-COOH） were investigated by spectroscopic analysis. Cell viability and cell apoptosis were applied to assessing the cytotoxicity of SWNT-COOH, cetyltrimethyl ammonium bromide （CTAB） and acid purified carbon nanotubes modified with cetyltrimethyl ammonium bromide （SWNT-COOH/CTAB）. The results indicate that SWNTs are more toxic than SWNT-COOH. Concentration and time-curve analyses indicate that cytotoxicity of SWNT-COOH/CTAB is more related to the toxicity of the surfactant CTAB. The cytotoxicity effect of CTAB and SWNT-COOH/CTAB is acceptable at low concentrations （0.5-25μg/mL）. The cytotoxicity observation suggests that SWNT-COOH/CTAB can safely applied to biomedical field at low concentrations （0.5-25μg/mL）.
