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The 'sacred leaf' or "Hoja Santa" (Piper auritum Kunth) has a great value for Mexican culture and has gained popularity worldwide for its excellent properties from culinary to remedies. To contribute to its heritage, in this project we proposed the green synthesis of silver oxide nanoparticles (Ag 2 O NPs) using an extract of "Hoja Santa" (Piper auritum) as a reducing and stabilizing agent. The synthesized Ag 2 O NPs were characterized by UV-Visible spectroscopy (plasmon located at 405 nm), X-ray diffraction (XRD) (particle size diameter of 10 nm), scanning electron microscopy (SEM) (particle size diameter of 13.62 ± 4.61 nm), and Fourier-transform infrared spectroscopy (FTIR) (functional groups from "Hoja Santa" attached to nanoparticles). Antioxidant capacity was evaluated using DPPH, ABTS and FRAP methods. Furthermore, the antimicrobial activity of NPs against a panel of clinically relevant bacterial strains, including both Gram-positive (Staphylococcus aureus) and Gram-negative bacteria (Salmonella Enteritidis and Escherichia coli O157:H7), was over 90% at concentrations of 200 µg/mL. Additionally, we assessed the antibiofilm activity of the NPs against Pseudomonas aeruginosa (reaching 98% of biofilm destruction at 800 µg/mL), as biofilm formation plays a crucial role in bacterial resistance and chronic infections. Moreover, we investigated the impact of Ag 2 O NPs on immune cell viability, respiratory burst, and phagocytic activity to understand their effects on the immune system., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)