Nano-bio interactions of Zno and graphene nanosystems: understanding the potential in vitro and in vivo response

Abstract

Nanomaterials possess unique physicochemical properties such as high reactivity, large surface to volume ratio, exceptional electronic characteristics and quantum size effects. A probable downside of these remarkable properties would be their enhanced interactions with biological systems, which may lead to potential toxic effects. Zinc oxide (ZnO) and graphene are two important nanomaterials that are extensively studied by the nanoscience community owing to their unique physico-chemical properties rendering wide range of potential applications. In the current Ph.D. work, we have extensively studied the specific role of size scale, and surface chemistry of zinc oxide nanocrystals (ZnO NCs) on its toxicity towards prokaryotic and eukaryotic cells. The results show that the toxicity towards bacteria increased with reduction in particle size (40nm and#8722;1.2µM) and with increasing concentrations (1mM and#8722; 7.5mM). Flow cytometry and confocal microscopy studies revealed that ZnO NCs undergo rapid dissolution in acidic (pH ~ 5-6) cancer microenvironment causing elevated ROS stress, mitochondrial superoxide formation, depolarization of mitochondrial membrane, and cell cycle arrest at S/G2 phase leading to apoptosis whereas normal cells having neutral pH remained unaffected at the same concentration. These results point to the interesting role of dissolution chemistry of nanomaterials under various bio-chemical environments in determining their toxicity. In case of graphene, where dissolution is a remote possibility, we have studied the role of surface chemistry in its nano-bio interaction. The interaction of graphene with kidney epithelial cells and macrophage cells showed that pristine graphene (p- G) accumulated preferentially on the plasma membrane leading to high oxidative stress. In contrast, carboxyl functionalized hydrophilic graphene (f-G) was internalized by the cells without causing much toxicity up to 48 h.