Nabeshi et al. Nanoscale Research Letters 2011, 6:93 http://www.nanoscalereslett.com/content/6/1/93 Page 4 of 6 Figure 2 Localization of unmodified and modified nanosilica in RAW 264.7 cells. RAW 264.7 cells were treated for 3 h with 100 μg/ml of fluorescent (green-F)-labeled nSP70 (a, b), nSP70-N (c), and nSP70-C (d) (green). The nucleus was counterstained using DAPI (blue). The original magnification of these photographs was × 63 (a) and × 100 (c, d). (b) is a magnified image of a portion of photograph (a). aggregation of intranuclear protein or inhibition of RNA transcription [26]. The said report [26] together with the results of this study suggests that silica nanoparticles enter the nucleus and induce inhibition of cell prolifera- tion. Hence, the nSP70-mediated cytotoxic effect may be related to nuclear localization. Investigating the cellular uptake/trafficking of indivi- dual nanosilicas is important for the development of safer forms of NMs. It is known that surface chemistry of nanoparticles, such as charge and the kind of modifi- cation group, affects their interaction with biological molecules [27]. For example, nanoparticles can induce different cellular responses by binding to proteins in the blood [28,29]. Bound proteins determine particle uptake by various cells and influence how nanoparticles interact with other blood components [30-32]. These findings suggest that surface modification alters the interaction between nanosilica and surrounding molecules, such as serum proteins, thereby altering the route of uptake into the cells. Mammalian cells ingest particulate matter by several routes, such as phagocytosis, macropinocytosis, clathrin-mediated, caveolin-mediated, and clathrin/ caveolin independent endocytosis [33-35]. Each route involves a unique set of receptors and acts on particular types of particles. The authors anticipate that surface modification of silica nanoparticles will influence their interaction with bloodborne macromolecules. Thus, nanoparticles decorated with different macromolecules will have different intracellular distributions. The authors are currently investigating the effects of nSP70, nSP70-C, and nSP70-N on cytotoxicity, protein adsorp- tion, cellular uptake, ROS generation, lysosomal stability, mitochondrial activity, activation of caspase 3 and 7, and mode of cell death (apoptosis versus necrosis).