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 (MnOx/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 MnOx were synthesized from ammonium iron(III) citrate and potassium permanganate at 70 degrees C for 12 h followed by annealing at 300 degrees 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 MnOx. 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 mu M. Our study shows its great potential for quantitation of fructose in honey samples. (C) 2019 Elsevier Inc. All rights reserved.