Nanomaterials possessing enzyme-like activity have been extensively studied owing to their high stability and tunable catalytic properties. In this work, a simple method has been developed for the synthesis of porous manganese oxide/manganese ferrite (MnO_x/MnFe₂O₄) nanopopcorns (MFNPs) in neutral media. The MFNPs exhibit dual enzymatic activities towards selective oxidation of ketoses followed by H₂O₂-induced decline of its catalytic activity. MFNPs, with MnFe₂O₄ as the core material and an outer layer rich in MnO_x, were synthesized from ammonium iron(III) citrate and potassium permanganate at 70 °C for 12 h followed by annealing at 300 °C for 6 h. The nanozyme, MFNPs, exhibited oxidase-like activity, which was proved by the oxidation of amplex red (AR) in the presence of dissolved oxygen in the solution, to form fluorescent resorufin. The activity of MFNPs is highly suppressed by H₂O₂ as a result of its induced dissolution of MnO_x. In addition, MFNPs having catalytic activity towards the selective oxidation of ketoses (e.g., fructose) followed by the formation of H₂O₂. The as-formed H₂O₂ diminished the catalytic activity of MFNPs for the AR oxidation to form fluorescent resorufin. Upon increasing fructose concentration, the fluorescence of resorufin decreases. Since the MFNPs do not show catalytic activity towards aldose sugars, such as glucose, sucrose, and mannose, the AR/MFNPs probe has high selectivity and sensitivity for detection of fructose with a limit of detection of 32 μM. Our study shows its great potential for quantitation of fructose in honey samples.