Synthesis and characterization of algae-coated selenium nanoparticles as a novel antibacterial agent against Vibrio harveyi, a Penaeus vannamei pathogen

Selenium is one of the essential elements with an important role in improving immune responses. Besides, in humans and animals, the element helps to resist infections. Selenium nanoparticles (Se NPs) have recently been examined for their biological activities. In this study, selenium nanoparticles (Se NPs) were synthesized using the microwave-assisted method under molar ratios of selenious acid to ascorbic acid ranging from 5:1 to 50:1 as starting materials and different irradiation times (5 to 15 min). The results showed that the size and morphology of the synthesized Se NPs were controlled by the selenious acid/ascorbic acid concentration ratio and the microwave irradiation time. The synthesized Se NPs with spherical morphology, small particle size (about 40 nm), and good colloidal stability were selected and coated with aqueous extract of Sargassum angustifolium. The antibacterial activity of the algae-coated and uncoated Se NPs was studied against Vibrio harveyi (a serious pathogen of Penaeus vannamei). In addition, the cytotoxicity of different concentrations (10 to100 μg/mL) of the Se NPs (algae-coated and uncoated) was investigated via the cell viability assay on two cultured cells; shrimp hemocyte and human lymphocyte. The results showed that the antibacterial activity of algae-coated Se NPs against Vibrio harveyi (MIC: 200 μg/mL) was improved compared to uncoated Se NPs (MIC: 400 μg/mL). The cell viability assay revealed that both the algae-coated and uncoated Se NPs showed toxicity effect neither on the human lymphocyte nor on the shrimp hemocyte at 25 μg/mL concentration after 48 h of incubation. Due to the antibacterial effects and no toxicity of the synthesized algae-coated Se NPs on both human and shrimp cells, the current study for the first time reports that the algae coated Se NPs can be considered for further investigation as a potential replacement for antibiotics in controlling Vibrio harveyi infections in Penaeus vannamei farming.