Modulating Pro- and Antioxidant Activities of Nanoengineered Cerium Dioxide Nanoparticles against Escherichia coli

Cerium dioxide nanoparticles (CeO2 NPs) exhibit both pro-oxidant and antioxidant properties against different cell organisms, irrespective of their shape, size, surface charge, or method of synthesis. The major factors that govern beneficial activities mainly arise from the presence of % Ce3+ on the surface of nanoparticles, redox potential of Ce3+/Ce4+ and surface modification that influences the electronic behavior of CeO2 NPs. The present study is focused on rationalizing these aspects, wherein nanoengineered CeO2 NPs are synthesized with surface modifying agents and explored as to how the physicochemical properties of nanoceria respond to the cell culture. For this purpose, 3-7 nm sized CeO2 NPs are evaluated for their toxicity, superoxide dismutase (SOD) mimic and oxidase activities against Escherichia coli. The toxicity, SOD mimic and oxidase activities for coated nanoparticles are found to be significantly higher owing to the interaction of surface coating with the cell membrane. These facets can be correlated with increased Ce3+ content on the surface of the nanoparticles as well as lowered Ce3+/Ce4+ redox potential as revealed from X-ray photoelectron spectroscopy and cyclic voltammetry measurements, respectively. As a consequence of these characteristics, the cell integrity is lost with cojoining of cells through outer membranes of E. coli. Interestingly, the generation of reactive oxygen species is found to be pronounced with poly(ethylene glycol) (PEG)-coated CeO2 NPs inducing toxic effects because of their internalization within cells. Thus, nanoengineered uncoated and glycine-coated nanoparticles exhibit antioxidant properties, while PEG-coated CeO2 NPs display the pro-oxidant nature as a consequence of the difference in surface chemistry as well as redox potentials.