, 2011). The cytotoxic effects for almost all kinds of metallic, metal oxide, semiconductor nanoparticles, polymeric nanoparticles and carbon based nanomaterials etc. have been reported. For establishing ‘safe’ nanotechnology it would be necessary to prove non-genotoxic nature of the nanomaterial in question. Several genotoxicity assays can be carried out in vitro. For example, in a recent article by Gonzalez et al. (2011) the applicability of in vitro micronucleus (MN) assay as described in OECD guideline signaling pathway for testing nanomaterials is reviewed. Several types of nanomaterials

were shown to induce a significant increase of MN frequencies. Based on the micronucleus test (MNinv) data on 21 nanomaterials, it was proposed that the in vitro MN test is quite appropriate to screen nanoparticles for potential genotoxicity. However it was recommended that protocols should be formulated to as to achieve maximum sensitivity and avoid false

negatives. Determination of the cellular dose, cytochalasin-B treatment, time of exposure, serum levels and choice of cytotoxicity assay was advised for a better interpretation of MN frequency results. The comet assay is a widely used in vitro assay in fundamental research for DNA damage and repair, in genotoxicity testing of novel chemicals and pharmaceuticals, environmental biomonitoring and human population monitoring. It has been employed for toxicity assessment of nanoparticles. In the article by Karlsson (2010) at least 46 cellular in vitro studies and several in vivo studies Doxorubicin using the comet assay have been reviewed. These studies had used the comet assay to investigate the toxicity of manufactured nanoparticles. Findings Inositol monophosphatase 1 indicate that majority of the nanoparticles exhibited high reactivity and cause DNA strand breaks or oxidative DNA lesions. Considering the sensitivity of the assay it

can enable the assessment of their relative potency. However, the author also states that, additional methods to measure DNA damage/genotoxicity should be employed and more studies investigating mutagenicity would prove valuable. Ames Test (or Bacterial Reversion Mutation Test) is yet another in vitro assay used to assess the genotoxic potential of nanomaterials. The test employs histidine dependent (auxotrophic) mutant strains of Salmonella typhimurium. This test is usually employed as an adjunct technique because it is difficult to interpret the data generated in a prokaryotic system to a eukaryotic genotoxicity testing. Furthermore results could be ambiguous in some instances when certain nanomaterials are not able to cross the bacterial wall or in situations where the nanomaterials are bactericidal. Singh et al. (2009) have reviewed the abilities of metal nanoparticles, metal-oxide nanoparticles, quantum dots, fullerenes, and fibrous nanomaterials, with reference to their potential to damage or interact with DNA.