Contribution of physicochemical characteristics of nano-oxides to cytotoxicity

To identify the key physicochemical properties of nano-oxides governing cytotoxicity, we investigate the contribution of the size, shape, morphology, and electronic properties of ten types of insulator (SiO2, CeO2 and Al2O3) and semiconductor (ZnO and CuO) nano-oxides to cytotoxicity using the NIH3T3 and A549 cell lines as models. We find that the shape of the Al2O3 (nanoparticle versus nanowhisker) and the morphology of the SiO2 (porous versus non-porous nanoparticles) did not have obvious effect on the observed cytotoxicity, and the size of the nano-oxides cannot be regarded as an indicator of cytotoxicity. By contrast, we find that the cell viability exposed to the semiconductor nano-oxides was much lower than that exposed to the insulator nano-oxides. Moreover, the Al-doped ZnO nanoparticle (NP) was more toxic than the non-doped ZnO NP, whereas the Al-doped CuO NP was less toxic than the non-doped CuO NP but more toxic than the Al2O3 NP. Correspondingly, the valence band X-ray photoelectron spectra of the nano-oxides show the density of states of the Al-doped ZnO NP (the Al-doped CuO NP) is higher (lower) than that of the non-doped ZnO NP (the non-doped CuO NP). These results suggest that the electronic properties of nano-oxides may play an important role in the observed cytotoxicity. The results have implications for selectively tailoring the toxic effect and establishing predictive models for the design of various types of nanomaterials with unique properties and for the understanding of interactions between nanomaterials with biological system.