296
toxic than the larger counterparts. However, when compared with Ag ions, Ag particles with size above 20 nm were found to be less toxic than Ag ions. On the contrary to the assumption that small-sized nanoparticles enter the cells more easily
causing damages, Yin et al. (2005) witnessed the in vitro effects of particle size on
the cytotoxicity of nickel ferrite in Neuro-2A cell line and concluded that the cytotoxicity was independent of the particle size (Yin et al. 2005). Thus, it can be
inferred that the mechanism of nanoparticle-mediated toxicity is complicated and
size cannot be regarded as the only influential parameter.
11.5.2 Effect of Shape and Structure
Apart from size, toxicity is also dependent on the shape and structure and has been
reported for myriads of nanoparticles. Difference in shapes and structure of nanomaterials like planes, spheres, fibers, tubes, polyhydra, etc. often results in alterations in their toxicity. In in vivo, membrane-wrapping processes during endocytosis
or phagocytosis are influenced by these ENPs. Endocytosis of spherical nanoparticles is reported to be faster and comparatively less toxic when compared to that of
rod or fiber-shaped nanoparticles. Nonspherical nanomaterials more likely flow
through capillaries causing other biological consequences (Gatoo et al. 2014).
Zhang et al. (2010) conducted a compared toxicity of graphene and carbon nanotubes and found an induction of concentration and shape-dependent cytotoxic
effects (Zhang et al. 2010). Moreover, even at low concentrations, graphene induced
a stronger metabolic activity emphasizing the effect of shape on cellular toxicity.
11.5.3 Effect of Surface Charge
Surface charge plays a crucial role in toxicity of ENPs as they interact with the biological systems. Surface charge primarily regulates (i) selective adsorption of
nanoparticles, (ii) colloidal behavior, (iii) plasma protein binding, (iv) blood–brain
barrier integrity, and (v) transmembrane permeability. Mostly, positively charged
NPs show enhanced opsonization as well as induce hemolysis and platelet aggregation in comparison to negatively charged and neutral nanoparticles (Goodman et al.
2004). For example, positively charged Si nanoparticles (Si–NP–NH 2 ) are more
cytotoxic in comparison to neutral and negatively charged ones (Bhattacharjee
et al. 2010).
D. Kundu et al.
toxic than the larger counterparts. However, when compared with Ag ions, Ag particles with size above 20 nm were found to be less toxic than Ag ions. On the contrary to the assumption that small-sized nanoparticles enter the cells more easily
causing damages, Yin et al. (2005) witnessed the in vitro effects of particle size on
the cytotoxicity of nickel ferrite in Neuro-2A cell line and concluded that the cytotoxicity was independent of the particle size (Yin et al. 2005). Thus, it can be
inferred that the mechanism of nanoparticle-mediated toxicity is complicated and
size cannot be regarded as the only influential parameter.
11.5.2 Effect of Shape and Structure
Apart from size, toxicity is also dependent on the shape and structure and has been
reported for myriads of nanoparticles. Difference in shapes and structure of nanomaterials like planes, spheres, fibers, tubes, polyhydra, etc. often results in alterations in their toxicity. In in vivo, membrane-wrapping processes during endocytosis
or phagocytosis are influenced by these ENPs. Endocytosis of spherical nanoparticles is reported to be faster and comparatively less toxic when compared to that of
rod or fiber-shaped nanoparticles. Nonspherical nanomaterials more likely flow
through capillaries causing other biological consequences (Gatoo et al. 2014).
Zhang et al. (2010) conducted a compared toxicity of graphene and carbon nanotubes and found an induction of concentration and shape-dependent cytotoxic
effects (Zhang et al. 2010). Moreover, even at low concentrations, graphene induced
a stronger metabolic activity emphasizing the effect of shape on cellular toxicity.
11.5.3 Effect of Surface Charge
Surface charge plays a crucial role in toxicity of ENPs as they interact with the biological systems. Surface charge primarily regulates (i) selective adsorption of
nanoparticles, (ii) colloidal behavior, (iii) plasma protein binding, (iv) blood–brain
barrier integrity, and (v) transmembrane permeability. Mostly, positively charged
NPs show enhanced opsonization as well as induce hemolysis and platelet aggregation in comparison to negatively charged and neutral nanoparticles (Goodman et al.
2004). For example, positively charged Si nanoparticles (Si–NP–NH 2 ) are more
cytotoxic in comparison to neutral and negatively charged ones (Bhattacharjee
et al. 2010).
D. Kundu et al.