Quantitative assay for the detection, screening and reactivity evaluation of nanoceria particles

Increasing use of engineered nanoparticles (NPs) in many industrial processes and consumer products requires rapid analytical methodologies to reliably detect and screen samples for the presence of NPs. Here, we report the development, analytical characterization and performance evaluation of a colorimetric assay as a comprehensive test for quantitative detection, screening and reactivity evaluation of nanoceria (cerium oxide, CeO₂) particles in aqueous environments. We provide a critical discussion of the role of environmental conditions including pH, ionic composition, and presence of humic acid and particle type on the overall performance and sensitivity of this assay. The method is based on the strong oxidation ability of nanoceria for organic dyes such as 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) and 3,3',5,5'-tetramethyl-benzidine dihydrochloride hydrate (TMB). Performance characteristics were established with a series of commercially available NPs of varying sizes dispersed in different environments. The results demonstrate that colorimetric assays can be used as a rapid and cost effective way to characterize nanoceria. The method enables identification and selective detection of nanoceria among other metal oxides including Fe₂O₃, TiO₂, Sb₂O₃, ZnO, SiO₂, and Al₂O₃. Applicability of the method for detection of nanoceria in environmental water samples is demonstrated. Recommendations are provided on the selection of the reaction conditions to ensure validity and reliability of measurements. The assay offers an effective and inexpensive alternative to advanced spectroscopic instrumentation, as a screening assay for nanoceria in environmental water. The method can be used as a general tool for the analytical characterization of redox active nanomaterials.