Malic acid as an organic linker for attaching Ag NPs to Fe3O4 nanoclusters: Synergistic enhancement of antimicrobial and antioxidant activities

The study presents a simple and user-friendly one-pot method for fabricating Ag@Fe 3 O 4 nanoclusters (NCs) and demonstrates their superior antimicrobial and antioxidant activity. In contrast, Ag NPs and Fe 2 O 3 NPs synthesized with ascorbic acid as a reducing agent showed no antimicrobial effectiveness. The fabrication process of Ag@Fe 3 O 4 NCs involved linking Ag NPs to Fe 3 O 4 NCs by hydrolyzing FeCl 3 to Fe(OH) 3 with NaOH, reducing Fe(OH) 3 to Fe(OH) 2 using malic acid, and then oxidizing Fe(OH) 2 with AgNO 3 . In the colloidal solution, malate ions from malic acid served as linkers, connecting Ag NPs to Fe 3 O 4 NCs through surface interactions. FESEM images showed smaller spherical Ag NPs attached to clusters of square-shaped Fe 3 O 4 particles, while FTIR analysis confirmed the presence of malate ions in the colloidal solution. The antimicrobial activity was assessed against Gram-positive bacteria ( B. cereus , MRSA), Gram-negative bacteria ( E. coli , P. aeruginosa , S. liquefaciens ), and yeasts ( C. albicans , C. tropicalis ), showing that Ag@Fe 3 O 4 NCs effectively eliminated both bacteria and fungi. MIC and growth curve investigations showed that even at very low concentrations, the individual components of Ag@Fe 3 O 4 NCs (Ag NPs and Fe 3 O 4 NCs) effectively synergize to inhibit bacterial growth. Additionally, the DPPH assay revealed that the antioxidant efficacy of Ag@Fe 3 O 4 NCs was also enhanced through this synergistic interaction. This combined effect is attributed to the external force exerted by Fe 3 O 4 NCs on the membrane, disrupting the cell wall and facilitating the entry of Ag NPs into the cell interior. Therefore, attaching Ag NPs to Fe 3 O 4 NCs in a colloidal solution represents a novel approach for optimizing both antimicrobial and antioxidant properties. Schematic illustration of the synthesis of Ag@Fe 3 O 4 NCs, their SEM micrograph, and their applications in antibacterial, antifungal, and antioxidant activities • Ag@Fe 3 O 4 NCs were strategically synthesized using a simple and user-friendly one-pot synthesis method. • Malic acid served both as a reducing agent and as an organic linker. • Ag NPs were attached to Fe 3 O 4 NCs in a colloidal solution via malate ions. • Ag@Fe 3 O 4 NCs exhibit strong and synergistic antimicrobial and antioxidant activities. • The synergistic mechanism involves the adherence of Fe 3 O 4 NCs to the cell membrane, followed by the internalization of Ag NPs.