Comparison of silver and gold nanoparticles green synthesis by <i>Artemisia annua</i> hairy root extracts

The green synthesis of metal nanoparticles (NPs) has garnered significant attention due to its simplicity, cost-effectiveness, and environmental sustainability. Gold NPs (AuNPs) and silver NPs (AgNPs) are widely employed across various industries, agriculture, and medicine owing to their unique physicochemical properties. This study explores the feasibility of synthesizing metal NPs through green methods using ethanolic (70%) extracts from Artemisia annua hairy roots. These extracts were found to contain reducing agents, primarily phenolic compounds, as identified by HPLC and MALDI-MS analyses. The phenolic compounds included hydroxybenzoic acids (e.g. p-coumaric and gallic acids) and hydroxycinnamic acids (e.g. caffeic acid and its derivatives such as chlorogenic, dicaffeoylquinic, and rosmarinic acids). The synthesis and structural characteristics of AuNPs and AgNPs were systematically compared. AgNPs formed a stable colloidal solution over extended periods, while AuNPs exhibited instability due to significant NP aggregation and precipitation. Furthermore, the photocatalytic activities of these NPs in the degradation of Methylene Blue were evaluated. AuNPs demonstrated substantial photocatalytic activity, whereas AgNPs exhibited negligible catalytic effects. This study highlights the potential and limitations of A. annua hairy root extracts in the biosynthesis of AuNPs and AgNPs, providing insights into their structural and functional differences.