Activated Carbon/Fe₃O₄/AgNPs Nanocomposites: In situ Synthesis from Papaya Seeds and Application for Ascorbic acid Detection

In this work, a novel papaya seed-based activated carbon/Fe₃O₄/AgNPs nanocomposite (MAC/Ag) was prepared via a one-pot in situ approach and used as a versatile peroxidase mimic for colorimetric detection of ascorbic acid (AA). The MAC/Ag nanocomposite exhibited enhanced peroxidase-like activity, catalyzing the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H₂O₂) and yielding colorimetric products. By optimizing the experimental conditions, the MAC/Ag-TMB-H₂O₂ detection platform displayed outstanding sensitivity towards AA, with an impressively low detection limit of 0.056 µM in the linear range of 25–500 µM. Notably, the platform demonstrated remarkable reusability and stability, maintaining a high level of activity even after numerous reuse cycles. The comprehensive investigation of the underlying mechanism revealed the crucial role of hydroxyl radicals. The successful quantitative analysis of AA in papaya juice verified the applicability of the MAC/Ag-TMB-H₂O₂ assay. These findings highlight the potential of the MAC/Ag nanocomposite as a reliable and reusable detection nanozyme for AA, offering promising prospects in environmental monitoring, biomedical diagnostics, and pharmaceutical analysis.