Green biosynthesis of selenium nanoparticles by a novel Monoraphidium sp.: optimization, bioinformatic insights, and nanoparticle characterization

Selenium nanoparticles (SeNPs) offer unique biomedical and industrial potentials with reduced toxicity compared to inorganic selenium, yet sustainable and eco-friendly production methods remain underexplored. As a novel approach, this study reports the first biosynthesis of SeNPs using a locally isolated Monoraphidium sp., alongside optimization of cultivation parameters and bioinformatic analysis. The microalga was isolated, morphologically and molecularly identified (GenBank accession PP375298.1), and phylogenetically analyzed. SeNP biosynthesis was assessed under varying sodium selenite concentrations (16-64 mM), pH values (5, 7, 9), and illumination cycles (8-24 h light). Qualitative analysis via SEM-EDX and XRD confirmed the amorphous nature and elemental composition of the nanoparticles, while quantitative characterization involved zeta potential and dynamic light scattering. Optimal SeNP production occurred at 32 mM sodium selenite, pH 7, 24 h illumination, and a cell density of 1.5 × 10⁷ cells/mL, yielding spherical SeNPs (122 ± 10 nm; −42 ± 0.6 mV) with ∼19% elemental selenium. Bioinformatic analysis indicated close genetic affinity to Monoraphidium sp. strains with potential high metabolic adaptability. The optimized process demonstrates a practical, green route for SeNP biosynthesis using Monoraphidium sp., providing genetic insights and practical parameters for sustainable nanomaterial production with promising commercial applications in biomedical and pharmaceutical industries.