Determination of antimicrobial and antioxidant activity of nanoparticles synthesised by biosynthesis from algae

In this study, we synthesized nanoparticles by biosynthesis from aqueous extracts of macroalgae (Codium fragile, Amphiroa rigida and Sargassum vulgare) belonging to three different divisions (Chlorophyta, Rhodophyta and Phaeophyta), The synthesized nanoparticles were designed to determine the usability of the synthesized nanoparticles in other fields, especially in health and for this purpose, silver (AgNPs), iron oxide (FeONPs) and zinc oxide (ZnONPs) nanoparticles were synthesized. The algae used in the study demonstrated the potential of algae as a sustainable resource in nanotechnology through green synthesis without the use of toxic chemicals. The obtained nanoparticles were subjected to various analytical and microscopic characterization techniques, including UV-Vis, FTIR, SEM, FESEM and EDS, and the results showed uniformly dispersed nanoparticles, the majority of which were smaller than 10 nm, with surface aggregates originating from the biocomposites in the algal extracts, indicating the efficiency of biological synthesis and stabilization of the particles. Silver nanoparticles biosynthesized by all algal species showed very high efficacy in inhibiting the growth of bacterial and fungal strains resistant to conventional antibiotics. FeO nanoparticles prepared by Sargassum vulgare, Amphiroa rigida and Codium fragile extracts show strong activity against antibiotic-resistant bacteria and fungi, while ZnO nanoparticles of all algal species are moderately to strongly active against bacterial and fungal strains. This activity is attributed to the active interaction between the metal core and algae-derived surface-active compounds (e.g. phenols, polysaccharides, proteins). Antioxidant assays such as DPPH, FRAP and TPC revealed that the synthesized nanoparticles were able to significantly combat oxidative stress and scavenge free radicals effectively. Silver nanoparticles showed a much higher antioxidant activity against free radicals compared to both the algal extracts from which they were synthesized and the standard substance used. Iron oxide nanoparticles also exhibited strong antioxidant effects in all algal species used. Zinc oxide nanoparticles syinthesized by Amphiroa rigida extract showed very high, moderate by Codium fragile extract and high by Sargassum vulgare extract. These results indicate that phenolic compounds were successfully integrated into the nanoparticle structure from the algal extract and the surface coating was realized effectively. These results show that phenolic compounds present in algae extracts were successfully incorporated into the nanoparticle structure and that these compounds coated the nanoparticles giving them strong antimicrobial and antioxidant activity. These results show that algae-assisted green synthesis is a promising biotechnological method to produce multifunctional nanoparticles in a sustainable, safe, and environmentally friendly manner, and reveal its potential for widespread use in medical applications such as antimicrobial and antioxidant.