Mono- and Bimetallic Au(Core)-Ag(Shell) Nanoparticles Mediated by Ulva reticulata Extracts

This research reports the fabrication of silver, gold and gold-silver bimetallic nanoparticles (NPs) using aqueous extracts of green marine alga Ulva reticulata. Analysis by UV-Vis spectrometry, X-ray diffraction, energy dispersive X-ray spectroscopy, scanning electron microscopy, transmission electron microscopy and Fourier transform infrared spectroscopy confirmed the biosynthesis of NPs by the seaweed extract. Surface plasmon resonances (SPR) were recorded at 439, 539 and 528 nm for silver (AgNPs), gold (AuNPs) and bimetal (Au core-Ag shell) NPs, respectively. AgNPs and AuNPs were mostly spherical in shape with size range of 7 to 36 and 19 to 32 nm, respectively, whereas Au-Ag NPs showed core-shell formation with star like structure shaped nanoparticles with size range of 57 to 230 nm. The results confirmed that Au ions reduced faster than Ag and the resultant bimetallic nanoparticles arrangement were found to be Au core and Ag shell. Chemical constituents such as ulvan and other polysaccharides of the green seaweed extract were identified as reducing and stabilizing agents for nanoparticles formation.