Green Synthesis of Silver Nanoparticles Using Extract of <i>Artemisia absinthium</i> L., <i>Humulus lupulus</i> L. and <i>Thymus vulgaris</i> L., Physico-Chemical Characterization, Antimicrobial and Antioxidant Activity

The novelty of this study is twofold: AgNPs were obtained and characterized using Artemisia absinthium (A. absinthium), Humulus lupulus (H. lupulus), and Thymus vulgaris (T. vulgaris) plants extracts; moreover, a green and environmentally friendly approach for the synthesis of silver nanoparticles (AgNPs) using aqueous extracts was developed. This paper discusses new approaches about the synthesis of AgNPs. T. vulgaris, H. lupulus, and A. absinthium, which are renewable and common plants, perfect as reducing, stabilizing, and capping agent for green synthesis of silver nanoparticles (AgNPs). The extracts and synthesized AgNPs were characterized by various physico-chemical, phytochemical, morphological scanning electron microscope (SEM/EDS) and transmission electron microscope scanning (TEM), and antibacterial activity. The antioxidant activity of extracts and AgNPs were also assessed by 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS•+), 2,2-diphenyl-1-picrylhydrazyl (DPPH•), cupric reducing antioxidant capacity (CUPRAC), ferric reducing antioxidant power (FRAP), and trifluoperazine dihydrochloride (TFPH•) scavenging assays. Extracts/AgNPs showed significant antioxidant activity in all cases. A. absinthium/AgNPs, H. lupulus/AgNPs, and T. vulgaris /AgNPs displayed activities against DPPH• (0.14 ± 0.00; 0.11 ± 0.00 and 0.14 ± 0.00 mmol/g), ABTS•+ (0.55 ± 0.05; 0.86 ± 0.05 and 0.55 ± 0.05 mmol/g), respectively. TEM analysis confirmed the average particle size, it estimated t A. absinthium/AgNPs–46 nm, H. lupulus/AgNPs size of synthesized particles was 42 nm and T. vulgaris/AgNPs–48 nm. SEM analysis revealed that T. vulgaris/AgNPs showed in solitary cases as snowflake-like, branched, but in a general spheric shape, H. lupulus/AgNPs were wedge-shaped, and A. absinthium/AgNPs were the spherical shape of the synthesized AgNPs. EDS analysis confirmed the purity of the synthesized AgNPs with a strong signal at 3.2 keV. A. absinthium/AgNPs, H. lupulus/AgNPs, and T. vulgaris/AgNPs exhibited higher antibacterial activity against all tested bacterial strains compared to their respective pure extracts. It is concluded that AgNPs synthesized in extracts have a broad range of biological applications, which can be used as an eco-friendly material without having negative effects on the environment