Nanomaterials are actively involved in enormous novel technologies and industrial products. Surface reactivity of nanomaterials are underlined to not only cases where the reactivity is unitized for benefits, e.g., nano-catalyst or nano-antibiotics, but also cases where nanomaterials undergo undesirable reactions once they are released from products, e.g., causing oxidative stress to cells or damaging cell membranes, and pose potential risks to the environmental and human health. Many assays were used to assess surface reactivity of nanoparticle (NP) colloids in liquid solution. They are often fulfilled by setting the NPs of interest as a reactant in a reaction, whose procession can be analyzed by a instrument, such as absorbance or fluorescence microscopy, due to the sensitive signal response of the other reactant or product under the analysis. In many cases, a single assay was applied; yet under few circumstances is fully examined whether the applied reactivity assay is sufficiently representative to the material’s intrinsic property that is truly relevant to what is studied. Consequently different assays were often interchangeably used and interpreted, and whether they imply the same intrinsic property of the material was not carefully inspected. In this study, we choose four commonly adopted reactivity assessment assays, namely methylene-blue reduction catalyzing assay (MRCA), ferric reducing assay (FRA), XTT superoxide detecting assay (XTT assay), and reactive oxygen species detection by EPR (ROS-EPR assay), and apply them to typical metal and oxide NP colloids, including Au, Ag, SiO2 and CeO2. Under each assay, we analyze the four NP colloids and rank the obtained reactivity magnitude of them by the specific assay. We contrast the reactivity magnitude pattern across the four NP colloids given by different assays. Overall, we conclude that the experimentally assessed surface reactivity information of NP colloids in liquid solution is dependent on the assay that is applied, arguing that we should be extremely careful about interchangeably using or interpreting reactivity of the same NP colloids obtained by different assays. We further propose that, for NP colloids in solution, a selected assay mechanistically assesses the intrinsic material property of redox activity or catalytic activity, the discrimination of which is critical to effective comparisons of NP colloids’ surface reactivity.

Issue of interchangeable use of reactivity assessment assays for nanoparticle colloids in liquid solution

253rd National Meeting (2017)

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