Green Synthesis of ZnO Nanoparticles Using Myrcia Oblongata DC: An Ecological Alternative for Biomedical Applications

The sustainable synthesis of metal oxide nanomaterials is a growing demand in nanobiotechnology, where ecological routes must deliver reproducible control over composition, crystallinity, and bioactivity. Here, we report the first green synthesis of zinc oxide nanoparticles (ZnO_MO NPs) using the aqueous extract of Myrcia oblongata DC, a native Myrtaceae species rich in polyphenols and terpenoids. Beyond introducing this novel plant-based route, the study provides insights into how specific phytochemical groups – especially phenolic and terpenoid compounds – can mediate Zn2+ complexation and hydrolysis, nucleation, and surface stabilization, contributing to a broader understanding of plant-assisted ZnO formation. The biosynthesized nanoparticles were systematically characterized by FTIR, XRD, DLS, HRTEM, UV–visible spectroscopy, photoluminescence (PL), and TGA. The ZnO_MO NPs exhibited a hexagonal zincite structure, high crystallinity, and an organic surface layer (≈ 45%) derived from plant metabolites, as confirmed by TGA and phenolic quantification (33.06 µg GAE mg⁻¹). UV–Vis and PL analyses revealed characteristic optical features of biofunctionalized ZnO nanostructures, indicating the presence of surface- and defect-related electronic states associated with the phytochemical capping. Compared to commercial ZnO NPs, ZnO_MO NPs displayed over twofold higher antioxidant capacity (690.6 vs. 311.2 µmol TE g⁻¹ in the ABTS assay) and a markedly lower polydispersity index (0.087 ± 0.014), indicating enhanced colloidal homogeneity. Cytotoxicity assays revealed preferential toxicity toward glioblastoma (U87) cells while maintaining biocompatibility with non-tumoral keratinocytes (HaCaT), demonstrating a moderately selective and biocompatible therapeutic profile (SI₅₀ ≈ 1.45). These findings establish M. oblongata as a novel phytochemical platform for engineering multifunctional, biofunctionalized ZnO nanostructures and highlight the potential of green nanotechnology to generate biocompatible and selective materials for future biomedical applications.