Nostoc sp.-mediated silver nanoparticles: biosynthesis, characterization, antibacterial activity, and cytocompatibility assessment.

The present study investigated the green synthesis of silver nanoparticles (N-AgNPs) using an aqueous extract of a locally isolated Nostoc sp. and evaluated their physicochemical characteristics, antibacterial activity, and cytocompatibility. Biosynthesized N-AgNPs were characterized by UV-Vis spectroscopy, FTIR, XRD, and SEM analyses. UV-Vis analysis confirmed nanoparticle formation through the appearance of a characteristic surface plasmon resonance band around 430 nm. SEM observations of dried samples revealed particle sizes ranging from 22.04 to 128.43 nm, with an average size of approximately 68 ± 27 nm. However, it should be noted that transmissio electron microscopy, dynamic light scattering, and zeta potential analyses were not performed in this study; therefore, the hydrodynamic size, size distribution in suspension, and colloidal stability of the nanoparticles remain to be characterized in future investigations. The antibacterial activity of N-AgNPs was assessed against Staphylococcus aureus and Pseudomonas aeruginosa using agar well diffusion and minimum inhibitory concentration (MIC) assays. N-AgNPs exhibited enhanced antibacterial activity compared with the crude Nostoc extract at several tested concentrations, with statistically significant differences observed in selected treatments (p < 0.05). The MIC values of N-AgNPs were 78.12 µg/mL against S. aureus and 156.25 µg/mL against P. aeruginosa, indicating stronger activity against the Gram-positive strain. Cytocompatibility was evaluated using fibroblast cells. N-AgNPs demonstrated concentration-dependent cytotoxicity, while maintaining acceptable cell viability at lower concentrations. The estimated IC50 value was approximately 1750 µg/mL (1.75 mg/mL), suggesting a relatively broad concentration window between antibacterial efficacy and cytotoxic effects. Overall, the findings demonstrate that Nostoc-mediated biosynthesis represents a promising environmentally friendly approach for producing biologically active silver nanoparticles with antibacterial potential. Future studies incorporating advanced nanoparticle characterization, molecular identification of the cyanobacterial isolate, and comparative evaluation against standard antibiotics will further clarify their potential for biomedical and antimicrobial applications.