Green synthesis, characterization, and biofunctional evaluation of chitosan-MgO@Ag nanocomposites using Eucalyptus camaldulensis leaf extract for antimicrobial and mitochondria-mediated anticancer activities.

The study describes the eco-friendly fabrication of chitosan-MgO@Ag nanocomposites (chitosan-MgO@Ag NCs) using an aqueous leaf extract of Eucalyptus camaldulensis, which serves as a natural reducing and stabilizing agent during synthesis. Fresh, disease-free leaves were processed to obtain a phytochemical-rich extract, which facilitated the phytoreduction of Ag+ ions and stabilized the composite matrix. Chitosan, MgO nanoparticles, and biosynthesized Ag nanoparticles were successfully integrated to form a stable NC system, which was comprehensively characterized using UV-visible spectroscopy, FTIR, XRD, DLS, zeta potential, SEM, TEM, SAED, and EDX analyses. UV-Vis analysis showed characteristic peaks at 244.81 and 418.32 nm confirming Ag nanocluster formation, while FTIR verified functional group interactions among chitosan, MgO, Ag, and E. camaldulensis biomolecules; XRD revealed distinct crystalline phases of MgO and Ag, DLS indicated a uniform hydrodynamic diameter of 242.3 nm with a zeta potential of - 25.3 mV, and SEM/TEM along with EDX confirmed well-dispersed spherical nanoparticles and homogeneous elemental distribution. Biological activity assessment demonstrated potent and dose-dependent antimicrobial effects against bacterial and fungal organisms, with S. typhi, C. perfringens, and K. pneumoniae showing high susceptibility. The NCs also exhibited significant anticancer activity against colon cancer cells (HCT-116), with IC50 values of 25 µg/mL (24 h) and 12 µg/mL (48 h). Increased intracellular ROS production, disruption of mitochondrial membrane potential, AO/EtBr-assisted apoptosis, and modulation of apoptotic gene expression (downregulation of Bcl2; upregulation of cytochrome c, caspase-3, Bax) collectively confirmed mitochondria-mediated apoptotic cell death. These findings highlight the broad-spectrum antimicrobial efficacy and strong pro-apoptotic anticancer potential of green-synthesized chitosan-MgO@Ag NCs, suggesting their applicability in biomedical, therapeutic, and antimicrobial formulations.