Abstract:
Cytotoxicity of carbonized metal-organic framework ZIF-8 on E. coli was evaluated
in terms of growth curves and colony forming units (CFU) counts after 36 hrs
exposure. Broth cultures of E. coli with carbonized ZIF-8 concentrations ranging
from 0 to 900 μg/ mL were placed in a shaker at a speed of 120 rpm and
temperature of 37 °C. The growth curve and CFU determination of all
concentrations affirmed carbonized ZIF-8 was nontoxic to E. coli. Separate growth
curves were derived for broth cultures with the raw materials of ZIF-8, including
zinc nitrate hexahydrate and 2-methylimidazole. Zinc nitrate hexahydrate
completely inhibited the bacterium growth at ZIF-8 equivalent concentrations of
800 and 1000 μg/mL, while in all the concentrations of 2-methylimidazole, the
typical growth pattern of E. coli was observed. The phenomena suggested that zinc
ions were the chemical origin of toxicity. Characterization of carbonized ZIF-8 by Xray
photoelectron spectroscopy, x-ray diffraction spectroscopy, and infrared
spectroscopy suggested the formation of nano ZnO, Zn, and C during the 2 hrs
carbonization at 800 °C. Nano-pores were formed due to the dissociation of
framework to encapsulate ZnO. As a result, the toxicity of ZnO to E. coli decreased.
Carbonization is applicable to reduce the toxicity of metal-organic frameworks that
would be used at high doses. Further toxicology evaluations using S. aureus also
showed similar results.
