<![CDATA[The green synthesis of copper-based nanomaterials utilizing plant extracts has attracted significant attention; however, controlling oxidation state and understanding its impact on biological performance remain challenging. In this present study, mixed-phase copper nanostructures were synthesized using aqueous stem bark extract of Annona muricata as a dual reducing and stabilizing agent under mild conditions. Phytochemical analysis revealed a high total phenolic content (310 mg GAE/g), thus confirming the strong redox capability for Cu2+ reduction. UV–Vis spectroscopy indicated the formation of nanoparticle with a characteristic absorption band at approximately 360 nm. XRD and EDS analyses were conducted to confirm the coexistence of Cu (0), Cu2O, and CuO phases. The crystallite sizes of these phases ranged from 22 to 28 nm, thereby suggesting partial oxidation during synthesis. The utilization of Fourier-transform infrared spectroscopy (FTIR) analysis has been demonstrated to be a valuable tool in the identification of the involvement of polyphenolic functional groups in reduction and surface stabilization processes. SEM and TEM observations revealed the presence of quasi-spherical nanoparticles with a mean diameter of 4 -16 nm, exhibiting signs of partial aggregation. The antimicrobial performance of the synthesized nanostructures exhibited a concentration-dependent response. While limited antibacterial activity was observed against Staphylococcus aureus and Escherichia coli, a pronounced antifungal effect was obtained against Candida albicans with an inhibition zone of 27.81 mm at 20% concentration. The pronounced antifungal activity exhibited a strong correlation with the presence of mixed copper phases, suggesting that the oxidation-induced surface chemistry and controlled Cu2+ ion availability may contribute significantly to the observed efficacy. These findings highlight the functional role of oxidation in plant-mediated copper nanostructures and demonstrate their potential as selective antifungal agents. This work provides insight into the relationship between phase composition and biological activity in green-synthesized copper nanomaterials. The remarkable selectivity exhibited by these mixed-phase nanostructures against fungal pathogens positions them as a viable, eco-friendly alternative for targeted antifungal applications, thus overcoming the limitations of conventional non-specific antimicrobial agents.]]>
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