  The ability to mimic protein-based oxidase with multi-functional inorganic
nanozymes would greatly advance biomedical and clinical practices. Praseodymia
(PrOx) nanorods (NRs) and nanoparticles (NPs) have been synthesized using
hydrothermal and precipitation methods. Both PrOx catalysts with different
morphologies exhibit significantly higher oxidase-like activities
(Michaelis-Menten constant Km < 0.026 mM) than commercial PrOx and most
so-far-reported artificial enzymes. One of the substrates, dopamine, can be
oxidized and further polymerized to generate polydopamine in acidic conditions.
Akin to CeO2, which is a well-studied nanozyme, a different mechanism involving
holes+, oxygen vacancies and oxygen mobility over PrOx catalysts has been
proposed in this work. However, fluoride ions were found to impose opposite
effects on the oxidase-mimicking activity of PrOx and CeO2, implying a
promising path for the exploration of new nanozymes. In support of this, PrOx
was further applied in colorimetric sensing of L-cysteine and fluoride with
high sensitivity.
