Green synthesis of silver nanoparticles using Padina commersonii: Characterization, hypoglycemic effects, and...

Nanotechnology is a dynamic field comprising chemistry, physics, biology, and engineering, with a high proficiency in disease treatment delivery methods. Metallic precursors (e.g.,AgNO₃) are widely used to synthesize NPs. But, owing to their harmful nature and the cost of these metallic nanoparticles, the focus is shifting toward "green synthesis" of nanoparticles using fungi, bacteria, plants, and algae. Hence, we used Padina commersonii to green synthesize NPs. We focused on the antioxidant, hypoglycemic, and antimicrobial efficacy of biologically synthesized AgNPs from P. commersonii.

Silver NPs (AgNPs) were synthesized using 80% methanol extract of P. commersonii upon removal of pigments and polysaccharides. Methanol (80%) was selected for higher polyphenol yield (∼30% w/w) compared to aqueous extracts (∼12% w/w), critical for efficient Ag⁺ reduction. Major phytochemicals, including fucoidan, phlorotannins, flavonoids (quercetin), and terpenes, are present in 80% methanol extract of P. Commersonii The NPs were characterized using ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, dynamic light scattering, energy dispersive X-ray (X-ray diffraction (XRD), and scanning electron microscopy (SEM). Antioxidant potential was determined using DPPH and ABTS scavenging assays, while hypoglycemic activity was conducted using alpha-glucosidase and alpha-amylase enzyme inhibitory assays. Finally, antimicrobial activities were conducted against S. aureus, E. coli (bacteria), and the fungal strains Candida albicans and Aspergillus niger.

The AgNPs were confirmed by the colour change from yellow to brown. Further, the UV and Raman spectrophotometry peaks, respectively, at 424 nm and 335 cm^-1, confirmed the presence of AgNPs. The average AgNPs size of 73.19 nm was obtained using the dynamic light scattering(DLS) technique, while the zeta potential indicated its stability at -21.5 mV. The SEM imaging confirmed a smooth surface with no aggregation, whereas the XRD pattern perceived the crystalline nature of these AgNPs. The antioxidant potential of AgNPs was higher than (DPPH: IC₅₀: 271.17 ± 3.992 and ABTS: IC50 195.03 ± 5.7535 µg/mL) the methanol extract. Similar patterns were observed with the hypoglycemic potential with α-glucosidase (IC50:161.74 ± 3.992 µg/mL) and α-amylase inhibitions (IC50: 176.70 ± 5.7535 µg/mL). The antimicrobial efficacy of AgNPs was evident for studied bacterial species (S.aureus:12.77 ± 0.58 mm; E.coli:15.27 ± 0.58 mm) and fungi (A. niger: 18.10 ± 0.15 mm; C.albicans: 17.4 ± 0.57 mm).

The AgNPs displayed potent antidiabetic and antimicrobial efficacy, suggesting their potential as viable alternatives to conventional antibiotic and antidiabetic drugs.