Biogenic Synthesis of Selenium Nanoparticles Mediated by Red Algal Biomass Extract (Kappaphycus alvarezii)

The biomass of the red macroalga Kappaphycus alvarezii has attracted scientific interest due to its biotechnological potential, as it contains bioactive compounds. These compounds may act as reducing and stabiling agents during the green synthesis of nanoparticles. Among these, selenium nanoparticles (SeNPs) stand out due to the properties of selenium and their potential applications in agriculture, including effects on plant growth, development, and stress responses. In this context, this study aimed to evaluate the processing and aqueous extraction of K. alvarezii biomass, as well as to establish experimental conditions for the biogenic synthesis of SeNPs. The biomass was supplied by Algastech and subjected to washing, drying at 40 °C, and grinding using a blade mill. Aqueous extracts were obtained through solid–liquid extraction at a ratio of 1:10 (w/v). The solution was sonicated at frequencies ranging from 10 to 50 Hz and heated in a water bath at 60 °C for 20 minutes. After extraction, The solution was then filtered. The resulting extract was analyzed for total polyphenol and flavonoid contents and used in SeNP synthesis, employing sodium selenite (Na₂SeO₃) as a precursor. Different extract concentrations (10, 25, 50, and 100%), Na₂SeO₃ concentrations (2.5, 5, 7.5, and 10 mmol L⁻¹), pH values (3, 6, 8, 10, and 12), temperatures, and reaction times (60 min at 30 °C and 30 min at 50 °C) were evaluated, and nanoparticle formation was monitored by UV–Vis spectrophotometry. The 100% extract presented the highest polyphenol and flavonoid contents, with 71.15 ± 2.796 mg gallic acid equivalents g⁻¹ dry weight and 400.20 ± 15.718 mg rutin equivalents g⁻¹ dry weight, respectively. The values obtained differ from those reported for K. alvarezii in previous studies, in which phenolic compound contents varied according to the solvent, processing method, biomass origin, and cultivation conditions, highlighting the influence of these variables on the phytochemical composition of the alga. The use of K. alvarezii in the green synthesis of nanoparticles has been described for different metallic systems, including silver and iron oxide nanoparticles, indicating the potential of this macroalga as a source of compounds with reducing and stabilizing properties. For SeNP synthesis, the selected conditions were 50% extract, 5 mmol L⁻¹ Na₂SeO₃, pH 8, 30 °C, and 60 min. Under these conditions, UV–Vis spectrophotometry revealed an absorption band in the 250–350 nm range, suggesting the possible formation of SeNPs. The production of SeNPs expands the applications of K. alvarezii as a biological matrix for the green synthesis of nanomaterials. The results demonstrate the potential of this species as a source of bioactive compounds for the green synthesis of SeNPs and establish initial conditions for their physicochemical characterization and subsequent evaluation of bioactivity in plant species of agricultural interest.

Acknowledgments: CAPES/DAI - N°88887.208038/2025-00