Spectroscopic analysis confirms the interactions between single walled carbon nanotubes and various dyes commonly used to assess cytotoxicity

The cytotoxicity of single walled carbon nanotubes was evaluated in the A549 human alveolar carcinoma cell line. Cell viability was assessed using the following indicator dyes, Commassie Blue, Alamar Blue^TM, Neutral Red, MTT and WST-1. Exposure of the A549 cells revealed the nanotubes to have low acute toxicity, however considerable variation was found depending on the dye employed. Spectroscopic analysis of the nanotubes' interactions with the dyes revealed interactions in all cases, resulting in the reduction of the associated absorption/fluorescent emission which is used to evaluate particle toxicity. In addition to being sensitive, simple, safe and cost-effective the ideal test for in vitro cell cytotoxicity must also not interfere with the compound to be tested. Our results therefore comprehensively confirm that the indicator dyes used in this study are not appropriate for the quantitative toxicity assessment of carbon nanotubes highlighting the pressing need for the development of alternative screening techniques.