Synthesis, process optimization and characterization of gold nanoparticles using crude fucoidan from the invasive brown seaweed Sargassum muticum

Crude fucoidans from Sargassum muticum obtained by hot water extraction at 40–80 °C were used for the synthesis of gold nanoparticles (AuNPs). The effect of operation temperature on the yield and properties of the extract was determined. The alginate fraction partially coextracted precipitated as calcium alginate and showed rheological properties slightly lower than those of commercial alginates reported elsewhere. The fraction of fucoidan with a larger amount of sulfate, obtained at 60 °C (45% saccharide, 22% fucose, 24% sulfate), also contained 8.5% phlorotannins and 3% protein, as well as showing 37% the 2,2-azinobis(3-ethyl-benzothiazoline-6-sulfonate) (ABTS) radical scavenging capacity of Trolox. This soluble product was used for optimization during the synthesis of AuNPs. Several reaction conditions were tested until the obtainment of homogeneous nanoparticles. The characterization of the synthesized nanoparticles was performed employing ultraviolet-visible spectroscopy, Z potential, transmission electron microscopy and Fourier transformed infrared spectroscopy.