Rosmarinus officinalis-based Ag/SiO2 and CeO2-Ag/SiO2 core-shell nanocomposites: A green approach to phytochemical analyses, molecular docking, antioxidant and antimicrobial applications with enhanced biocompatibility

• Ag/SiO 2 and CeO 2 -Ag/SiO 2 nanocomposites were synthesized using rosemary extract. • Heterogeneous morphology with spherical and irregular particles. • Significant antioxidant, antifungal, and antibacterial activities. • Promising binding affinities to thymidylate kinase. • Potential for healthcare and environmental remediation. Antimicrobial resistance (AMR) is a pressing global health crisis. To address this challenge, we synthesized novel Ag/SiO 2 and CeO 2 -Ag/SiO 2 nanocomposites (NCs) using a green and sustainable approach, employing Rosmarinus officinalis (rosemary) leaf extract as a reducing and stabilizing agent. The synthesized nanocomposites were characterized using various techniques, in which the results verified valuable insights into the structural, morphological, and optical properties. Consequently, the multiple beneficial properties of the nanocomposites were investigated, for instance, phytochemical contents, antioxidant properties, and biological activities. The characterization of the nanocomposites using different techniques verified a heterogeneous morphology, well-dispersed nanoparticles, and a high surface area. The phytochemical analyses verified rich levels of phenolics (118.56 mg gallic acid/g dry extract) and flavonoids (56.23 mg catechin acid/g dry extract) of rosemary extract. Ag/SiO 2 NC demonstrated significant antioxidant activity using the DPPH assay, reaching 84.1 % scavenging at 0.38 mg/mL. Additionally, both nanocomposites demonstrated promising antimicrobial activity against various pathogenic microorganisms with superior performance for CeO 2 /Ag/SiO 2 NC (e.g. inhibition zone diameter= 13.0 ± 1.55 mm against S. epidermidis ) in comparison to Ag/SiO 2 NC. Both Ag/SiO 2 and CeO 2 /Ag/SiO 2 demonstrated antifungal activity against M. phaseolina with MIC at 175 µg/mL and 93 µg/mL, respectively. Molecular docking simulations revealed promising binding affinities of bioactive molecules to the target protein. The findings suggest that rosmarinic acid, hydrogenated rosmarinic acid, and gentamycin could be promising candidates for further development of antibacterial agents targeting thymidylate kinase. The green synthesis approach, combined with the inherent antimicrobial properties of rosemary extract and the unique characteristics of the nanocomposites, offers a promising strategy for addressing the growing threat of AMR. This research has potential applications in various fields, including healthcare, agriculture, and environmental remediation.