Marine Algae for Antimicrobial Applications: Silver Nanoparticles Prepared With <i>Sargassum Cymosum</i> Extract

Abstract We describe the synthesis of silver nanoparticles (AgNPs) using the aqueous extract of the brown macroalga Sargassum cymosum for metal reduction and nanoparticle stabilization. It consists of a low cost, simple, and versitile protocol employing an abundant renewable natural material. Conditions for the green synthesis of the AgNPs were screened by the evaluation of the individual effect of the experimental variables employing UV–vis spectrophotometry and results show that once enough amount of alga extract is provided, an alkaline pH and a midly high temperature (60 °C) favor faster nanoparticle formation. Characterization analyses by dynamic light scattering (DLS) and transmission electron microscopy (TEM) show that the AgNPs were mostly spherical irrespective of the synthesis experimental conditions, but mean diameters are lower when the AgNPs are prepared at alkaline pHs (&lt; 5 nm) as compared to neutral pH conditions (10–50 nm). AgNPs were stable for at least nine months when stored at room temperature in white opaque PET flasks, with no significant aggregation. Antibacterial activities for selected assays of the AgNPs were evaluated against the Gram‐positive Staphylococcus aureus , as well as the Gram‐negative Escherichia coli and Pseudomonas aeruginosa , and the minimal inhibitory concentration (MIC) determined for all bacteria was 51.2 µg Ag mL −1 .