Synthesis, optimization, and physicochemical characterization of selenium nanoparticles from polysaccharide of mangrove Rhizophora mucronata with potential bioactivities

Selenium (Se) is considered an important micronutrient for human and animal health having potential biological functions and it is required for the prevention and treatment of diseases. The present study was designed to optimize the synthesis conditions of selenium nanoparticles by the Taguchi design method using sodium selenite as a precursor, ascorbic acid as a reductant, and Rhizophora mucronata leaves polysaccharide (RMLP) as a stabilizing agent. In the present studies, RMLP-SeNPs were synthesized by using a polysaccharide (RMLP) that was previously isolated from mangrove Rhizophora mucronata leaves. The synthesized RMLP-SeNPs were characterized by UV-Vis, HR-TEM, DLS, FTIR, and TGA-DSC analysis. In addition to this, in vitro antibacterial activity of RMLP-SeNPs was determined by using the disk diffusion method according to the standard protocols. Antibiofilm activity of RMLP-SeNPs was determined by 96-wells polystyrene microtiter plate methods. Moreover, in vitro, antioxidant capacity such as ABTS, DPPH, and reducing power of RMLP-SeNPs was evaluated. The result demonstrates that the optimal condition for the synthesis of RMLP-SeNPs was 2 h of reaction time, 0.04 M of Vc concentration, 1 mg/mL of RMLP, and pH 7.5. The particle size of synthesized RMLP-SeNPs was around 54.85 nm under optimal conditions by DLS measurement. HR-TEM results showed that RMLP-SeNPs were a uniform spherical shape with an average size of 31.82 nm. UV-vis analysis showed the synthesis of RMLP-SeNPs with a characteristic peak at 265 nm which was further confirmed by FTIR and EDX spectrum. Further, the RMLP-SeNPs show excellent scavenging capacity on DPPH, ABTS, and reducing power as compared to other forms of selenium. Moreover, the RMLP-SeNPs show good antimicrobial and antibiofilm activity against tested strains such as Aeromonas hydrophila, Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa and exhibited a lesser toxic effect in brine shrimp lethality assay. These findings provide an opportunity to use selenium nanoparticles in food industries, biomedical, cosmetics, and pharmaceutical applications, especially to develop novel antioxidant and antimicrobial compounds.