Fig. 3. (A) The visual color changes and absorbance spectra of TMB. (1) Control, (2) 2.5 μg mL⁻¹ Mn₃O₄ and (3) 5.0 μg mL⁻¹ Mn₃O₄. (B) Time-dependent absorbance changes of TMB at 652 nm in the presence of Mn₃O₄ microspheres. (C) The oxidase-like activity of Mn₃O₄ microspheres was dependent on pH. TMB: 0.416 mM, Mn₃O₄: 5.0 μg mL⁻¹. (D) The oxidase mimetic activity of Mn₃O₄ microspheres was dependent on temperature. TMB: 0.416 mM, Mn₃O₄: 5.0 μg mL⁻¹. (E) The steady-state kinetic assay of Mn₃O₄ (5.0 μg mL⁻¹).