The two cells visible seem to be undergoing cell division. (A to H) Time points at 10 to 17 h, in 1-h increments. Given that graphene is thought to be the hardest material known [3], it is counterintuitive to believe that liver carcinoma cells are capable of folding and compartmentalizing graphene sheets. However, if these sheets contained structural defects such as point defects, single vacancies, multiple vacancies, carbon adatoms, dislocation-like defects, or edge defects, as extensively reviewed by Banhart et al. [26], the cells may be able to fold the sheets, one at a time, along

these TPCA-1 in vitro defect lines (in a ‘shedding nature’) and compartmentalize them within phagosomes or vesicles using reasonably low-energy processes. The defect content KU55933 in vivo of the SGS, in relation to the starting graphite material, can be indicated by the relative intensity of the Raman D band to G band ratio, located at approximately 1,350 and 1,580 cm−1, respectively [27]. Although the synthesis procedure and Raman characterization shown in Additional file 1: Figure S2 shows a weak D band enhancement after exfoliation due to functionalization of the graphitic edges, it remains unclear as to what defects, if any, are inherent

to the graphene nanoplatelets. Conclusions We have investigated the cytotoxicity and internalization of highly exfoliated, water-soluble SGSs when exposed in vitro to highly aggressive human liver cancer cells (SNU449 and Hep3B). Both MTT and WST-1 colorimetric assays displayed a similar concentration- and time-dependent cytotoxicity profile for concentrations of 0.1 to 10 μg/ml. Verubecestat ic50 These trends were also evident from LDH observations. However, the SGSs seemed to be toxic to both cell lines at the highest concentration of 100 μg/ml. We have also observed an interesting cellular internalization

phenomenon for graphene materials for the first time. The cancer cells were capable of internalizing relatively large SGSs with diameters comparable to the cells themselves as well as smaller SGS having heights indicative of single graphene sheets. Although not conclusive, there is evidence to suggest that due to graphene structural defects, the cancer cells are also able to actively fold and compartmentalize these sheets. We speculate that the Bcl-w findings reported here may encourage the development of SGSs for applications in drug delivery, medical imaging, and even hyperthermic cancer therapy by NIR and/or radio frequency heating. To date, such applications have been explored for more rigid carbon nanostructures such as fullerenes [28] and nanotubes [29–32], but a non-toxic, more flexible (foldable), and larger surface-area material as provided by graphene offers an alternative design strategy. Acknowledgments This work was funded by the NIH (U54CA143837), the NIH M.D.