Exploiting the Biogenic Potential of <i>Spirulina platensis</i> for the Sustainable Synthesis of Multifunctional and Bioactive Magnesium Oxide Nanoparticles

Antimicrobial resistance, largely driven by bacterial biofilm formation, remains a major challenge in treating immunocompromised patients, including those undergoing cancer therapy. In this study, magnesium oxide nanoparticles (MgO NPs) were synthesized via a green approach using Spirulina platensis extract. X-ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscopy confirmed their crystalline structure, uniform spherical morphology, and an average size of 20.19 nm. The NPs exhibited notable antioxidant activity (IC₅₀ = 82.75 µg/mL, DPPH assay) and strong reducing power in the ferric reducing antioxidant power assay. Antimicrobial testing showed broad-spectrum activity against Gram-negative and Gram-positive bacteria as well as Candida albicans, with a low minimum inhibitory concentration value (7.81 µg/mL). Moreover, MgO NPs disrupted preformed biofilms with 77.6% inhibition. Anticancer activity evaluation on HT-29 colorectal adenocarcinoma cells revealed dose-dependent cytotoxicity at 24 h, while non-cancerous cells retained high biocompatibility. Collectively, these findings highlight the potential of green-synthesized MgO NPs as eco-friendly multifunctional agents against biofilm-associated infections and cancer.