Abstract
Cerium oxide nanoparticles (nanoceria; CNPs) have been found to have both pro-oxidant and anti-oxidant effects on different cell systems or organisms. In order to untangle the mechanisms which underlie the biological activity of nanoceria, we have studied the effect of five different CNPs on a model relevant aquatic microorganism. Neither shape, concentration, synthesis method, surface charge (ζ-potential), nor nominal size had any influence in the observed biological activity. The main driver of toxicity was found to be the percentage of surface content of Ce3+ sites: CNP1 (58%) and CNP5 (40%) were found to be toxic whereas CNP2 (28%), CNP3 (36%) and CNP4 (26%) were found to be non-toxic. The colloidal stability and redox chemistry of the most and least toxic CNPs, CNP1 and CNP2, respectively, were modified by incubation with iron and phosphate buffers. Blocking surface Ce3+ sites of the most toxic CNP, CNP1, with phosphate treatment reverted toxicity and stimulated growth. Colloidal destabilization with Fe treatment only increased toxicity of CNP1. The results of this study are relevant in the understanding of the main drivers of biological activity of nanoceria and to define global descriptors of engineered nanoparticles (ENPs) bioactivity which may be useful in safer-by-design strategies of nanomaterials.
Highlights
Depend on the Ce3+/Ce4+ ratio at the particle surface
As there are so many contradicting reports regarding the effects of nanoceria and so many factors which may contribute to the biological effects, the aim of this study was to perform a thorough study of the effect of five different cerium oxide nanoparticles (CNPs) in an effort to untangle the mechanisms which underlie the biological activity of nanoceria
A strong absorption at 250 nm was observed in CNP1, which is directly related to Ce3+31
Summary
Depend on the Ce3+/Ce4+ ratio at the particle surface. In this regard, it has been reported that exposure of CNPs to phosphate shifted the redox state and altered their catalytic properties in vitro[18,19]. Besides cerium valence states at the surfaces of CNPs, there are a number of factors which may influence CNPs interaction and biological effects on living cells In this regard, a deep understanding of the colloidal chemistry of nanoceria (ζ -potential, solution pH, use of dispersants, particle size, etc.) in the tested biological media is of outmost relevance, processes such as aggregation/agglomeration have been found to modulate the toxicity of CNPs in aquatic organisms[24,25,27,28,29]. To get deeper insights into the biological mechanisms of CNPs, the colloidal stability and redox chemistry of the most and least toxic CNPs were modified and the effect of these modifications on the model organism were tested
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