Green synthesis of AuNPs using <i>Cistanche tubulosa</i> extract and their broad-spectrum antimicrobial, antiparasitic, and scolicidal activities

The green synthesis of metal nanoparticles has emerged as a promising alternative to traditional antimicrobial agents due to the simultaneous effects of metal nanoparticles and herbal products on antimicrobial properties. In this study, we present the one-step green synthesis of gold nanoparticles (AuNPs) using <i>Cistanche tubulosa</i> (<i>C. tubulosa</i>), a medicinal plant known for its diverse therapeutic properties, including antioxidant, anti-inflammatory, and antimicrobial effects. The synthesis was carried out by mixing the aqueous extract of <i>C. tubulosa</i> with tetrachloroauric acid (HAuCl₄), resulting in the reduction of gold ions and the formation of AuNPs. The time of 70 min was selected as the optimum reaction time by evaluating the absorption peak at 545 nm in UV-vis spectra. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images indicated AuNPs were successfully synthesized with quasi-spherical morphology in the particle size range of 20-70 nm. The synthesized AuNPs exhibited significant antibacterial activity against both Gram-positive and Gram-negative bacteria, including <i>Staphylococcus aureus</i>, <i>Escherichia coli</i>, and <i>Bacillus cereus</i>, with the best antibacterial activity being for <i>Bacillus cereus</i> with as low as a minimum inhibitory concentration (MIC) of 37.50 µg mL^-1. Furthermore, the AuNPs demonstrated potent antiparasitic activity against <i>Giardia lamblia</i>, a common protozoan parasite, with 100% inhibition at 120 µg mL^-1 for 480 minutes. The nanoparticles also exhibited excellent scolicidal activity against <i>Echinococcus granulosus</i> protoscolices, with 100% inhibition at 180 and 60 µg per mL AuNPs for 30 and 60 minutes, respectively. These findings indicate the promising potential of <i>C. tubulosa</i>-synthesized AuNPs as a solution for combating a wide range of infectious and parasitic diseases and an attractive alternative to conventional antibiotics and antiparasitic agents. This study lays the foundation for future research into the <i>in vivo</i> efficacy and clinical application of these green-synthesized gold nanoparticles in the treatment of infectious diseases.