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Abstract This study investigated the biosynthesis of selenium nanoparticles (SeNPs) using endophytic fungi isolated from eight plant species collected from different locations in Egypt representing diverse habitats. A total of tewenty fungal isolates were recovered and initially classified based on morphological and microscopical examination into 6 genera - Aspergillus, Alternaria, Fusarium, Mucor, Penicillium, and Rhizopus. The twenty fungal isolates were screened for their ability to extracellularly synthesize SeNPs in selenite-amended media, with eight isolates showing evidence of production. Two isolates - Penicillium citrinum and Rhizopus arrhizus - were selected for further characterization and optimization of SeNP production. Both fungi could tolerate up to 40mM selenite and reduced over 99% of 3mM selenite to elemental selenium under optimal conditions as determined by ICP-MS. The biosynthesis of SeNPs extracellularly by both fungi was frstly distinguished by the appearance of red color, then it was confrmed by an absorption peak in UV–Vis spectrum. The crystallinity and crystalline size of mycosynthesized SeNPs were also studied by XRD analysis. The difraction peaks for the SeNPs synthesized by both fungal strains confrm the hexagonal crystalline structure. SeNPs synthesized were spherical in shape with sizes between 50-80nm as revealed by TEM imaging. FTIR spectra of the two types of mycosynthetic SeNPs revealed vibrational bands of diferent functional groups in the range of (4000–400 cm−1) suggesting a mechanism for the process of SeNP synthesis by both fungi. FTIR spectral analysis manifested the presence of biomolecules and functional groups such as hydroxyl, amine, and lipids with SeNPs that have a role as reducing agents to convert selenite to elemental selenium, and as capping agents to avoid their agregation. |