Application of green silver nanoparticles synthesized from the red seaweeds Halymenia porphyriformis and Solieria robusta against oral pathogenic bacteria by using microscopic technique.

Aqueous extracts of two red seaweeds Halymenia porphyriformis and Solieria robusta were used to synthesize green silver nanoparticles. These biogenic nanoparticles were tested against four strains of oral pathogenic bacteria which cause tooth decay or cavities. Staphylococcus aureus (MT416445), Streptococcus viridans (MT416448), Lactobacillus acidophilus (MT416447) and Lactobacillus brevis (MT416446) were used. Characterization of AgNPs was done by UV-Visible spectroscopy, SEM, XRD and FTIR. XRD analysis revealed the crystalline nature of the particles. The size analysis by XRD of the green AgNPs by H. porphyriformis indicated it had smaller particles, 15.23 nm, when compared to AgNPs by S. robusta (17 nm). Both green synthesized silver nanoparticles showed moderate antibacterial activity against all strains of bacteria, except L. acidophilus. Both particles showed their maximum zone of inhibition against L. acidophilus at a lower concentration of 50 and 100 µg. However, it was concluded that silver nanoparticles of H. porphyriformis are more effective than that of S. robusta due to their smaller size.