Silver nanoparticles synthesized from marine algae Spatoglossum asperum: Antioxidant properties and seed germination enhancement

• AgNPs Synthesis : Silver nanoparticles were successfully synthesized using Spatoglossum asperum . • Enhanced antioxidant Activity : AgNPs showed higher antioxidant activity than algal extract in DPPH and FRAP assays. • Seed germination Boost : AgNPs improved Vigna radiata L. seed germination, reaching 95 % under both normal and saline conditions. • AgNPs Characterization : UV–Vis, FTIR, and XRD confirmed AgNPs cubic structure with a 23.05 nm crystallite size. • Morphology : SEM revealed spherical, cubical, and nanocluster particles averaging 43.65 nm. Biosynthesized silver nanoparticles (AgNPs) have shown promising potential in plant growth under stressed conditions but marine algae synthesized AgNPs still remain least explored. In the current study, AgNPs have been synthesis by using the aqueous extract of marine brown alga Spatoglossum asperum as a reducing medium and their application in the growth of Vigna radiata seeds under salt stress conditions was studied. The antioxidant potential of AgNPs in comparison with algal extract was also assessed. The AgNPs synthesized using the algal extract was characterized by means of UV–Vis spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray (XRD) diffraction analysis, Field emission scanning electron microscopy (FE-SEM) and Energy dispersive X-ray spectroscopy (EDS). The FE-SEM and EDS results confirmed the formation of multi-shaped (spherical, cubical and nano-clusters) particles with average size of 43.65 nm. Developed AgNPs showed a surface plasmon resonance band at 425 nm and a face-centric cubic crystallographic structure with an average crystallite size of 23.05 nm. The FTIR spectrum ensured the involvement of di and polysulphides in the synthesis of nanoparticles. The results revealed that the algal synthesized AgNPs showed superior antioxidant activity compared to the algal extract alone and significantly enhanced seed germination in Vigna radiata under both normal and saline conditions. These findings suggest that Spatoglossum asperum derived AgNPs could play a pivotal role in agriculture and environmental sustainability.