Biosynthesis, optimization, and characterization of biosynthesized selenium nanoparticles using the probiotic bacterium Limosilactobacillus fermentum

In this study, selenium nanoparticles (Se NPs) were biosynthesized, optimized, and characterized using the cell-free supernatant of Limosilactobacillus fermentum. Ultraviolet–visible (UV–Vis) spectroscopy was employed to monitor the formation of Se NPs under various experimental conditions. The optimal parameters for Se NPs biosynthesis were determined to be 70 mM sodium selenite (Na₂SeO₃), pH 6, and a 1:2 (v/v) ratio of cell-free bacterial metabolites to precursor solution, with incubation for 72 hours at 40 °C. Characterization of the synthesized Se NPs was performed using transmission electron microscopy (TEM), X-ray diffraction (XRD), UV–Vis spectroscopy, Fourier-transform infrared spectroscopy (FT-IR), and zeta potential analysis. The UV–Vis spectra showed an absorption peak between 250 and 280 nm, indicating successful nanoparticle formation. TEM images revealed the Se NPs to be homogeneous, rod-shaped structures with average diameters ranging from 30.45 to 52.21 nm. The zeta potential measurements indicated that the Se NPs carried a positive surface charge of +19.81 ± 6.14 mV, suggesting good colloidal stability. FT-IR analysis confirmed the presence of proteins acting as capping and stabilizing agents, as evidenced by characteristic symmetric and asymmetric amines bands at 2932 cm⁻¹. Additional peaks corresponding to aromatic and aliphatic C–N stretching were observed at 1676, 1533, 1411, 1141, and 1067 cm⁻¹. These findings demonstrate that L. fermentum, a probiotic bacterium, can be effectively employed in the green synthesis of Se NPs. This method presents a rapid, cost-effective, and environmentally friendly alternative to conventional chemical and physical nanoparticle synthesis techniques.