Biofabrication of noble monometallic platinum nanoparticles(Pt-NPs) and bimetallic gold–silver nanoparticles(Au Ag-NPs) using aqueous extract of Delonix regia is presented here. Antioxidant activity of biomatrix-loaded metallic nanoparticles is estimated for scavenging of two model radicals i.e., 2,2′-Azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt and 1,1′-Diphenyl-2-picrylhydrazyl. Broad spectral continuum spanning from visible to ultra-violet region(Pt-NPs: 30 min) and broad high intensity absorption peak around at 500 nm(Au Ag-NPs: 10 min) in two different UV–Visible spectra confirmed the biofabrication. Nanoparticles fabricated with distorted spherical shape and crystalline face-centred-cubic geometry. Strong signal around at 2.10 ke V(pure-phase platinum) and typical X-ray peaks observed at 2.20 and 3 ke V suggested, co-existence and alloying interaction of Au and Ag in Au Ag-NPs. ζ potential(-15.2 mV: Pt-NPs and -13.9 mV: Au Ag-NPs) values suggested surface adsorption of polyphenolic compounds to provide stability. Nanoparticles exhibited pronounced antioxidant activity against free radicals through their electron/hydrogen transfer ability.
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