Influence of Metal-Organic Framework ZIF-8 Nanomaterials on Escherichia coli

Abstract

Metal organic framework (MOF) nanomaterials have attracted special attentions in recent decades, because of unique structures, outstanding properties and wide applications. Among the most popular commercial MOF products is ZIF-8, due to the easy synthesis, high stability, and excellent gas separation performance. To ensure the safe applications, it is essential to investigate the toxicity of ZIF-8, in particular the environmental toxicity to microbial community. In this study, the microbial toxicities of ZIF-8 MOF were evaluated using E. coli as the model bacterium. ZIF-8 of 0 to 900 μg/mL was dispersed thoroughly in Luria–Bertani (LB) culture medium for E. coli exposure. The bacteria were counted in terms of colony forming units (CFU) on LB agar plates, and the growth curves were recorded on UVvis spectrophotometer. The results indicated that the growth was retarded with the increase of ZIF-8 concentration and completely annihilated at 900 μg/mL. The CFU was slightly stimulated at 400 μg/mL and reduced with the increase of ZIF-8 concentration to 600 and 800 μg/mL. The CFU value dropped to 0 at 900 μg/mL. Consistently, growth curves of E. coli showed the inhibitive effect of ZIF-8. Dosedependent decreases were observed at 200-600 μg/mL, while the growth was completely lost at 800 and 900 μg/mL. It should be noted that the starting material zinc nitrate hexahydrate (metal core of ZIF-8) showed even higher toxicity to E. coli which completely inhibited the growth at 400-900 μg/mL. In contrast, the chelating ligand 2-methylimidazole was nontoxic. Therefore, it is speculated that the toxicity of ZIF-8 was from the released Zn2+ rather than the chelating ligand from 2-methylimidazole. Our results suggested that ZIF-8 was toxic to bacteria at high concentration and the discharge of ZIF-8 should be restricted to avoid environmental pollution.