Phytosynthesis of stable Au, Ag and Au–Ag alloy nanoparticles using J. Sambac leaves extract, and their enhanced antimicrobial activity in presence of organic antimicrobials

• J. Sambac leaves extract reduces Au3+ → Au0, Ag+ → Ag0 and Au3+ + Ag+ → Au0 − Ag0 alloy.
• pH and redox potential values corroborated the reduction mechanism of metal ions.
• The spherical nature of particles (ϕ20–50 nm) is evident from FE-SEM and TEM images.
• The synthesized NPs show enhanced activity in presence of organic antimicrobials.

A green chemistry approach for the synthesis of Au, Ag and Au–Ag alloy nanoparticles (NPs) using the corresponding metal precursors and Jasminum sambac leaves extract as both reducing and capping media, under microwave irradiation, is reported. During the formation, as expected, the reaction mixture shows marginal decrease in pH and an increase in solution potential. The formation of NPs is evident from their surface plasmon resonance (SPR) peak observed at ∼555 nm for Au, ∼435 nm for Ag and ∼510 nm for Au–Ag alloy. The XRD pattern shows fcc structure while the FTIR spectra indicate the presence of plant residues adsorbed on these NPs. Such a bio-capping of NPs is characterized by their weight loss, ∼35% due to thermal degradation of biomass, as observed in TG analysis. The colloidal dispersion of NPs is stable for about 6 weeks. The near spherical shape of NPs (ϕ20–50 nm) is observed by FE-SEM/TEM images and EDAX gives the expected elemental composition. Furthermore, these NPs showed enhanced antimicrobial activity (∼1–4-fold increase in zone of inhibition) in combination with antimicrobials against test strains. Thus, the phytosynthesized NPs could be used as effective growth inhibitors for various microorganisms.

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