Subtle changes in the structure of nanoparticles influence their surface tension and corresponding interaction with cells and proteins. Here, the interaction of the single wall carbon nanotube (SWCNT) and multiwall carbon nanotube (MWCNT) with different surface tension with tau protein was evaluated using a variety of techniques including far and near circular dichroism, fluorescence spectroscopy, dynamic light scattering, Zeta potential, and TEM evaluation. Also the cytotoxicity of SWCNT and MWCNT on the PC12 cell line as a model of nervous system cell line was investigated by the MTT, LDH, acridine orange/ethidium bromide staining, flow cytometry, caspase 3 activity, cell and membrane potential assays. It was observed that SWCNT induced more structural changes of tau protein relative to MWCNT/tau protein interaction. It was also revealed that SWCNT and MWCNT impaired the viability and complexity of PC12 cells in different modes of cytotoxicity. Analysis of cellular outcomes indicated that MWCNT in comparison with SWCNT resulted in induction of necrotic modes of cell death, whereas apoptotic modes of cell death were activated in SWCNT-incubated cells. Together these findings suggest that surface tension may be used to determine how nanoparticle structure affects neurotoxicity and protein conformational changes.

OPEN Figure 1. Effect of SWCNT and MWCNT on cell membrane potential (CMP) in PC12 cells. The PC12 cells were incubated with different concentration of SWCNT (black) or MWCNT (gray) for 48 h. Data are shown as average of three separate experiments and error bars represent standard deviation (SD). * P < 0.05 and ** P < 0.01 represents the significant differences between CNTs -treated groups and control. # P < 0.05 and ## P < 0.01 represents the significant differences between SWCNT -treated groups and MWCNT -treated groups.