, 2006). In a review by Nel et al. (2006) a question, “Do nanomaterials properties necessitate a new toxicological science?” was raised. It was argued that the main characteristic of nanomaterials is their size in the transitional zone between individual

atoms or molecules and the corresponding bulk materials. This can modify the physicochemical properties of the material as well as create the opportunity for increased uptake and interaction with biological tissues (Chithrani et al., 2006 and Sonavane et al., 2008). This combination of effects can generate adverse biological responses in living cells see more otherwise not seen with the same material in larger (bulk) form (Nel et al., 2006). The increase in surface area determines the potential number of reactive groups on the particle surface. Table 1 summarizes the observed biological effects vis-à-vis physicochemical properties and the types of nanomaterials. Shape of the nanoparticles has been shown to have a pronounced effect on the biological activity. It is reported that silver nanoparticles undergo shape-dependent interaction with E. coli ( Pal et al., 2007); Chithrani et al. (2006) reported better uptake of spherical gold nanoparticles than gold nanorods in HeLa cells. In case of anatase TiO2 nanomaterial, it was shown that alteration to a fiber structure of greater Entinostat concentration than 15 μm created a highly toxic particle that initiated an inflammatory response by alveolar macrophages

and that length may be an important determinant of nanomaterial biocompatibility ( Hamilton et al., 2009). Another study by Journeay et al. (2008) demonstrated that water-soluble rosette nanotube structures display low pulmonary toxicity due to their biologically inspired design and self-assembled architecture. In a review on widely used metal oxide and carbon nanomaterials,

Landsiedel et al. (2010) emphasized that physico-chemical characterization Ribonucleotide reductase of nanomaterials and their interaction with biological media are essential for reliable studies. In a study with 1.5 nm sized gold nanoparticles it was observed that surface charge was a major determinant of their action on cellular processes; the charged NPs inducing cell death through apoptosis and neutral NPs leading to necrosis in HaCaT cells ( Schaeublin et al., 2011). Considering the physicochemical properties of various nanomaterials and their interactions with the biological environment, Maynard et al. (2011) state that the challenges presented by simple nanoscale materials such as TiO2, ZnO, Ag, carbon nanotubes, and CeO2 are now beginning to be appreciated. But these simple materials are merely the vanguard of a new era of complex materials, where novel and dynamic functionality is engineered into multifaceted substances. Further, according to Maynard et al. (2011), if we are to meet the challenge of ensuring the safe use of this new generation of substances, it is time to move beyond “nano” toxicology and toward a new toxicology of sophisticated materials.