Green-Synthesized Silver Nanoparticles Mediated by the Marine Macroalgae Chaetomorpha linum: Physicochemical Characterization, Antimicrobial and Antioxidant Activities

The green synthesis of silver nanoparticles (AgNPs) using marine macroalgae represents an environmentally friendly alternative to conventional chemical methods. In this study, silver nanoparticles (CL-AgNPs) were successfully synthesized using the aqueous extract of the marine green macroalga Chaetomorpha linum. The extract was characterized by HPLC-DAD and FTIR, revealing phenolic compounds and functional groups involved in nanoparticle reduction and stabilization. The synthesized CL-AgNPs were characterized by UV–Vis, FTIR, XRD, FESEM, EDS and DLS analyses, confirming the formation of predominantly spherical nanoparticles with an average particle size of 31.09 ± 2.52 nm (range: 21.26–42.90 nm) and a face-centered cubic crystalline structure. The antimicrobial and antioxidant activities of the synthesized nanoparticles were comprehensively evaluated and directly compared with those of the corresponding crude algal extract. Compared with the crude extract, CL-AgNPs exhibited enhanced antimicrobial activity, with minimum inhibitory concentration (MIC) values as low as 1.56 μg/mL, together with improved antioxidant activity in DPPH, ABTS, CUPRAC, and metal chelating assays. These findings demonstrate that C. linum-mediated AgNPs constitute a sustainable and promising nanoplatform for biomedical, pharmaceutical, food, and environmental applications.