Abstract

The present study reports the green synthesis of silver nanoparticles (AgNPs) using the red macroalga Scinaia moniliformis J. Agardh, an underexplored marine species rich in bioactive compounds. This eco-friendly method utilized the aqueous algal extract as a natural hydrophilic reducer and stabilizer. A visible color shift from light yellow to dark brown signified AgNP formation, which was further confirmed by characterization techniques including UV–Vis spectroscopy, FTIR, XRD, and TEM-SAED. A distinct surface plasmon resonance peak at 437 nm confirmed nanoparticle synthesis, while XRD validated their crystalline nature. FTIR indicated the presence of phenolics, proteins, and other biomolecules involved in reduction and capping. TEM analysis revealed predominantly spherical nanoparticles with an average size of 24.03 nm. Functionally, the AgNPs displayed strong antibacterial activity against both Gram-positive and Gram-negative bacteria, with the highest inhibition against Escherichia coli and Shigella dysenteriae. They also exhibited potent, dose-dependent antioxidant activity (IC50 = 41.09 ± 0.35 μg) and significant cytotoxicity against MCF-7 breast cancer cells (IC50 = 51.49 ± 0.45 μg). These findings underscore the novelty of using S. moniliformis for nanoparticle synthesis and highlight the broad biomedical applicability of the resulting AgNPs in antimicrobial and anticancer therapeutics.

Key words: Red macroalga; Silver nanoparticles; Antioxidant; Antibacterial; Anticancer