IntroductionThe trace element selenium is an essential micronutrient for the health of humans, animals, and microbesMany researchers have recently become interested in selenium nanoparticles (SeNPs) because of their biocompatibility, bioavailability, and low toxicity. Consequently, selenium nanoparticles are widely used in various biomedical applications and wastewater bioremediation due to their greater bioactivity. Green biosynthesis of nanoparticles is common and preferable nowadays.MethodsIn this work, the selenium nanoparticles were synthesized using the brown seaweed Polycladia myrica aqueous extract and characterized using seven parameters, SEM, TEM, UV spectra, Zeta potential, EDX, X-ray differaction and FTIR, then examined for their cytotoxicity using PC-3 cells and normal mammalian cells from the African green monkey kidney (Vero) were used to test the effectiveness of the produced Polycladia myrica mediated selenium nanoparticles as an anticancer agent and antiviral activity against HAV HM175 (Hepatitis A), HSV-2 (Herpes simplex II), and Adenovirus strain 2.ResultsThe phycosynthesized nanoparticles exhibit antiviral activity (40.25 ± 2.61, 8.64 ± 0.82, and 17.39 ± 1.45%) against HAV-10, Adenovirus, and HSV-2, respectively. The IC50 values of the two cell types human prostate PC-3 and Vero were 123.51 ± 4.07 g/mL and 220.53 ± 6.89 g/ mL, respectively. The maximum inhibitory percent was 86.15 ± 2.31 against PC-3 cells. At the same time, at a concentration of 125 g/mL.DisscusionThis work showed that PoSeNPS have good antiviral activity against HAV-10 virus with an antiviral percent of 40.25%, despite weak antiviral activity against Adenovirus and HSV-2 with antiviral percent (8.64% and 17.39%), respectively. The cytotoxicity effect of these nanoparticles was determined against PC-3 with a maximum inhibitory percent of 80.53%. These nanoparticles have no hazardous effect against normal Vero cells as the viability percent was (78.39% and 49.23%) for Vero cells and PC-3 cells, respectively, at 125 μg/mL.