Size- and dose-dependent cytotoxicity of ZIF-8 based on single cell analysis

ZIF-8 nanoparticles (NPs) has been demonstrated with good potential in drug delivery, which causes an increasing attention on relevant toxicity study. In this work, MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide), glutathione (GSH), reactive oxygen species (ROS), stain analysis and gene detection assays were performed on ZIF-8 (50, 90 and 200 nm) incubated HepG2 cells. Moreover, time-resolved inductively coupled plasma mass spectrometry (TRA-ICP-MS) was applied for single cell analysis; the variation in cellular zinc amount and the proportion of zinc up-taken cells was investigated as a function of NPs size, incubation concentration/time and elimination. Smaller size of ZIF-8 NPs would lead to higher zinc accumulation and toxicity. The function of ZIF-8 on cells is assumed to be mainly related to zinc intracellular accumulation. The possible action path is presented as high accumulation of zinc in ZIF-8 incubated cells lead to high ROS level and cellular inflammation, ultimately inducing necrocytosis. For better understanding of the bio-effect of ZIF-8, ZnO NPs and Zn²⁺ incubated HepG2 cells were evaluated in the same way. Higher accumulation of zinc in larger part of the cell population was found in ZIF-8 incubated cells than that in ZnO NPs incubated cells. It demonstrated higher bioavailability for ZIF-8 over ZnO NPs. While, in drug delivery application, the possible risk of the remained intracellular ZIF-8 cannot be ignored.