OICC Press Journal of Nanostructure in Chemistry 2193-8865 10 4 (December 2020) 2020 09 23 Synthesis of silver and gold nanoparticles by Sargassum muticum biomolecules and evaluation of their antioxidant activity and antibacterial properties 10.1007/s40097-020-00352-y EN N. González-Ballesteros Departamento de Química Inorgánica, Centro de Investigaciones Biomédicas (CINBIO), Universidade de Vigo, Vigo, ES M. C. Rodríguez-Argüelles Departamento de Química Inorgánica, Centro de Investigaciones Biomédicas (CINBIO), Universidade de Vigo, Vigo, ES M. Lastra-Valdor Centro de Investigación Marina, Universidade de Vigo, Vigo, ES G. González-Mediero Servicio de Microbiología, Complejo Hospitalario Universitario de Vigo (CHUVI), Vigo, ES S. Rey-Cao Servicio de Microbiología, Complejo Hospitalario Universitario de Vigo (CHUVI), Vigo, ES M. Grimaldi Dipartimento Scienze Chimiche, della Vita e della Sostenibilità Ambientale, Università di Parma, Parma, 43124, IT A. Cavazza Dipartimento Scienze Chimiche, della Vita e della Sostenibilità Ambientale, Università di Parma, Parma, 43124, IT F. Bigi Dipartimento Scienze Chimiche, della Vita e della Sostenibilità Ambientale, Università di Parma, Parma, 43124, IT IMEM Parma-CNR, Parma, 43124, IT Journal Article 2020 09 23 Abstract Abstract The present work reports on the antibacterial and antioxidant activity of gold and silver nanoparticles, synthesized by an extract of the brown macroalga Sargassum muticum (SM). These nanoparticles were synthesized and fully characterized by means of UV–Vis spectroscopy and electron microscopy. These techniques confirmed that spherical nanoparticles, with mean diameters of 10.4 ± 1.2 nm for Au@SM and 41.0 ± 5.7 nm for Ag@SM, were formed. To investigate the possible role of these biomolecules in this green synthetic process, Fourier-transformed infrared spectroscopy analysis was performed before and after the synthesis of nanoparticles. Furthermore, the carbohydrate composition was examined along with other variations observed after the synthesis of nanoparticles by size-exclusion chromatography. The study of the changes observed indicated that the polysaccharide fraction of the extract plays a role in the formation of the nanoparticles as well as in their stabilization. The in vitro antioxidant activity was analyzed by the determination of the reducing power, total content of phenolic compounds and the 2,2-diphenyl-1-picryl-hydrazyl (DPPH) scavenging activity. Lastly, the antibacterial activity was tested against three types of bacteria with different cell wall composition. In particular, Ag@SM showed good inhibitory capacity on Gram+, especially on Staphylococcus aureus with a MIC of 3.38 µg/mL. Graphic abstract