where [E] signifies the molar concentration of Fe present in the OA nanozyme, as ascertained from nanoparticle tracking analysis (NTA) data and the indirect element atomic ratio quantification profile from XPS. The number/concentration of particles was estimated as 2.27 × 10 7 particles per mL. It was assumed that each nanozyme constituted a spherical particle exhibiting a specific radius, as determined by morphological analyses.