Self‐limited Phosphatase‐mimicking CeO₂ Nanozymes

Abstract

CeO2 nanoparticles or nanoceria is a very interesting enzyme mimic (nanozyme) with a diverse range of catalytic activities. Most of the previous studies focused on its redox chemistry for mimicking oxidase, peroxidase, and catalase‐like activities, and as a scavenger of reactive oxygen species. Considering CeO2 has both Ce(III) and Ce(IV) species and both interact strongly with inorganic phosphate, nanoceria has also been studied for its phosphatase‐like activity. We herein compared these species along with alkaline phosphatase (ALP). First, CeO2 and Ce(IV) have good activity using p‐nitrophenylphosphate (p‐NPP) as a substrate, while other metal ions failed to show this activity. Since a reaction product is inorganic phosphate and we observed an interesting enzyme kinetic profile, the effect of phosphate was studied, which inhibited both CeO2 and ALP. The inhibition constant was about 5‐fold smaller for CeO2. The inhibition effect of polyphosphates was even stronger. Due to the product inhibition effect, CeO2 is unlikely to be a typical multiple turnover nanozyme, and the system is self‐limited. For the other anions, only F− showed a moderate inhibition effect on the cerium species, while adsorption of DNA did not inhibit the activity. Finally, heat treated ALP lost the activity, but CeO2 and Ce(IV) remained active. This study has deepened our understanding of CeO2 as a phosphatase mimicking nanozyme, which could be useful for biosensing and chemical biology applications.

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“…[105] As one of the lanthanides, due to oxygen can reversibly binding and shifting between the Ce 3+ and Ce 4+ , the Ce nanoparticles exhibit excellent free radical scavenging activity. [106,107] Thus, the Ce based nanomaterials have been widely used as nanozymes to removing O 2 −• and • OH. For ceria oxides, the CeO 2-x nanorods with different aspect ratios have reported by Neville et al to mimic haloperoxidase (Figure 5B).…”

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“…Besides mimicking the structure and function of natural enzymes, enzyme mimic nanomaterials are more stable, more controllable, and more natural to prepare at a lower cost. CeO 2 -NPs have become one of the research proprieties because of their multiple enzyme activities, 31,32 such as mimetic activities of superoxide dismutase, 33 catalase, 7 phosphatase, 34,35 peroxidase, 36 oxidase, 37 and others. Although studies have illustrated that the mimic activities of phosphatase and catalase follow different chemical methods and involve different active sites, 38 the more complex mechanisms warrant further study.…”

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“…On the other hand, phosphatase mimics can be employed as a class of hydrolases in nanozyme-based pesticide assays. In these systems, phosphatase-like nanozymes produce quantitative information through hydrolyzing OPs [36].…”