Green synthesis and characterization of <i>Blumea sinuata</i> silver nanoparticles: antibacterial, antifungal, and antioxidant properties

The plant <i>Blumea sinuata</i> (Lour.) Merr. harbours high amounts of phytoconstituents, some of which have strong reduction and capping potential. Eco-friendly and nontoxic silver nanoparticles have been synthesized using the plant extract of <i>B. sinuata</i>. The formation of <i>B. sinuata</i> silver nanoparticles (BS-Ag₂O NPs) was confirmed through various techniques. UV-visible spectroscopy revealed an absorbance band at 408 nm, Fourier transform infrared spectroscopy (FTIR spectroscopy) identified functional groups serving as stabilizing and capping agents, essential for the formation of silver nanoparticles, dynamic light scattering (DLS) measurement indicated that the nanoparticles had a mean hydrodynamic diameter of 102.50 nm, and the evaluated zeta potential for surface charge analysis of BS-Ag₂O NPs was found to be -16.4 mV. High-resolution transmission electron microscopy (HRTEM) showed an average particle size of 7.98 nm, and X-ray diffraction (XRD) analysis confirmed the face-centred cubic (FCC) structure of Ag₂O NPs. The antibacterial activity of BS-Ag₂O NPs against phytopathogenic bacteria <i>Erwinia carotovora</i>, <i>Ralstonia solanacearum</i>, and <i>Xanthomonas oryzae</i> was assessed by the agar-well diffusion method. At 400 μg concentration of BS Ag₂O NPs, the maximum zones of inhibition were 20.66 mm and 20.33 mm against <i>E. carotovora</i> and <i>R. solanacearum</i>, respectively. While a zone of inhibition of 14.33 mm was observed against <i>X. oryzae</i>. Biogenic BS-Ag₂O NPs exhibited remarkable antifungal activity against phytopathogenic fungi, namely <i>Alternaria alternata</i>, <i>Aspergillus niger</i>, <i>Aspergillus flavus</i>, and <i>Fusarium oxysporum</i>. At a concentration of 1.5 mg mL^-1 BS-Ag₂O NPs, the percentage of inhibition was 91.70, 62.65, 58.96, and 50.45 on the growth of <i>A. alternata</i>, <i>A. flavus</i>, <i>A. niger</i>, and <i>F. oxysporum</i>, respectively. The antioxidant activity of BS-Ag₂O NPs was evaluated by 2,2-diphenyl-1-picrylhydrazyl hydrate (DPPH) as well as 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) methods. The reported DPPH free radical scavenging activity was 25.85 ± 0.36% at 80 μg mL^-1 concentration of BS-Ag₂O NPs, and in the case of ABTS, it was found to be 40.28% at 80 μg mL^-1 concentration of BS-Ag₂O NPs.