Nanotechnology has emerged as a transformative force in modern medicine, enabling the development of innovative diagnostic and therapeutic agents. In this study, we report the biogenic synthesis and characterization of iron oxide (Fe), platinum (Pt), and composite Fe/Pt nanoparticles (NPs) using an aqueous extract of Ocimum araratum. The extract demonstrated high antiradical activity (IC₅₀ = 0.39 ± 0.09 mg/mL) and sufficient flavonoid content, facilitating the reduction and stabilization of metal ions during nanoparticle formation. The synthesized nanoparticles exhibited average hydrated sizes ranging from 417 to 490 nm, with the smallest dimensions recorded for Fe/Pt composites. The cytotoxic potential of the nanoparticles was evaluated in vitro using the A549 (ATCC CCL-185) lung carcinoma cell line via MTT assay. While Fe NPs exhibited moderate cytotoxicity at higher concentrations (IC₅₀ = 0.38 mg/mL, or 0.95 μg/well), Pt and Fe/Pt nanoparticles demonstrated lower, dose-dependent cytotoxicity, indicating a more favorable safety profile. Notably, none of the synthesized nanoparticles displayed antibacterial activity against Escherichia coli K-12, suggesting specificity toward cancer cells rather than microbial targets. These findings underscore the advantages of using plant-based, environmentally friendly synthesis approaches to produce biocompatible nanoparticles with potential theranostic applications. The integration of Pt with Fe in a single nanocomposite offers both therapeutic and diagnostic functionalities, aligning with the goals of personalized medicine. Overall, the study supports the potential of Fe/Pt nanocomposites as multifunctional nanomaterials for future biomedical applications, particularly in targeted cancer therapy and diagnostics.