Banana Calyx Derived Iron Nanoparticles with Superior Peroxidase Like Activity for Colorimetric Detection of Ascorbic Acid in Sapota Fruit Samples

ABSTRACT This work reports a sustainable biotemplate‐assisted approach for the synthesis of iron oxide nanoparticles (FeNPs) using banana calyx, designed as a green nanozyme platform for sensitive detection of ascorbic acid (AA) in food matrices such as sapota. The nanoparticles were extensively characterized by SEM, TEM, XRD, FTIR, and UV–Vis spectroscopy confirming the predominant formation of crystalline α‐Fe 2 O 3 structures suitable for catalytic applications. The FeNPs exhibited remarkable peroxidase‐like activity, catalyzing the oxidation of 3,3’,5,5’‐tetramethylbenzidine (TMB) in the presence of H 2 O 2 under mild conditions. Kinetic analysis revealed a high catalytic efficiency with a V max of 49 × 10 − ⁸ M/s and a low K m of 0.163 mM, underscoring their strong substrate affinity. Using this activity, a colorimetric assay was developed for AA detection, demonstrating a low detection limit of 0.516 µM, excellent linearity ( R 2 > 0.99) across a wide concentration range, and strong selectivity against common interfering ions and biomolecules. Recovery studies in spiked sapota samples yielded 94%–100%, highlighting accuracy and reproducibility. Furthermore, the assay successfully differentiated healthy sapota (79.94 µM AA) from fungal‐infected fruits (29.5–41.03 µM), validating its applicability for nutritional assessment. These findings establish the use of an underexplored, abundantly available agricultural residue banana calyx‐derived FeNPs as a sustainable nanozyme system. The material demonstrates high efficiency for antioxidant sensing and food quality monitoring.