Biogenic synthesis of bioactive zinc nanoparticles from cyanobacterial Nostoc sp. MK-7 for biomedical applications

This study reports the green synthesis of bioactive zinc oxide nanoparticles (MK-7 ZnO NPs) using Nostoc sp. strain MK-7 extract as a natural reducing and stabilizing agent. The formation of ZnO NPs was confirmed by UV-visible spectroscopy with a characteristic absorption peak at 312 nm. FTIR analysis revealed the involvement of bioactive functional groups (O-H, C = O, C-O, and Zn-O), indicating their role in nanoparticle reduction and stabilization. XRD analysis confirmed the crystalline nature of the nanoparticles with a prominent peak at 36.3°, and the average crystallite size was calculated to be 41.9 nm using the Debye-Scherrer equation. FESEM and TEM analyses demonstrated a well-defined hexagonal morphology, while EDS confirmed high zinc purity (82.3% by weight). Biological evaluations revealed that MK-7 ZnO NPs exhibited significantly enhanced bioactivity compared to the crude extract. The nanoparticles showed strong antioxidant activity, achieving 89.04% ABTS radical scavenging with an IC₅₀ value of 35 ± 5 µg/mL and superior ferric- and cupric-reducing capacities. In elastase inhibition assays, MK-7 ZnO NPs demonstrated notable anti-wrinkle potential (50.5% inhibition at 100 µg/mL; IC₅₀ = 55 ± 5 µg/mL). Importantly, the nanoparticles significantly reduced viability of MDA-MB-231 breast cancer cells by inducing apoptosis, as confirmed by Annexin V-FITC/PI staining and flow cytometry. Furthermore, MK-7 ZnO NPs suppressed nitric oxide production and downregulated IL-6 secretion and mRNA expression, demonstrating potent anti-inflammatory and anticancer effects. Overall, the findings highlight the successful biosynthesis of structurally stable, hexagonal MK-7 ZnO NPs with enhanced antioxidant, anti-inflammatory, anti-wrinkle, and anticancer activities. These results underscore the promising potential of MK-7 ZnO NPs as multifunctional therapeutic agents, warranting further in vivo investigations for clinical translation.