Green synthesis and characterization of silver nanoparticles from the aerial parts of Leucas lanata with enhanced antioxidant and antimicrobial activities

Abstract In the present study, a green, Phyto-assisted approach was employed to synthesize silver nanoparticles (AgNPs) using the aqueous extract of the aerial parts of Leucas lanata . The successful formation of AgNPs was evidenced by a characteristic surface plasmon resonance (SPR) band at 384 nm in the UV–Vis absorption spectrum. Elemental mapping and energy-dispersive X-ray (EDX) analysis further confirmed the presence of silver, showing a prominent peak at 2.7 keV. X-ray diffraction (XRD) patterns revealed distinct crystalline planes, which were consistent with the results of Selected area electron diffraction (SAED). High-resolution transmission electron microscopy (HRTEM) determined an average particle size of 25.37 nm. The nanoparticles exhibited a high zeta potential value, suggesting strong stability attributed to phytochemical-mediated capping, as corroborated by Fourier transform infrared spectroscopy (FT-IR). The biosynthesized L-AgNPs displayed potent antioxidant activity with an IC₅₀ value of 49 µg/mL in the DPPH assay. L-AgNPs exhibited a higher proportion of ABTS scavenging activity (12.26%) than the Leucas lanata extract at a lower concentration of 100 µg/mL, indicating enhanced antioxidant potential. Similarly, the FRAP value of L-AgNPs (21.56 ± 0.17 µM at 100 µg/mL) was significantly greater than that of the aqueous plant extract, further confirming their superior reducing capacity. Moreover, the silver nanoparticles demonstrated significant antimicrobial activity against Staphylococcus aureus, Escherichia coli, Salmonella abony, and Bacillus subtilis. The MIC value for Leucas lanata aqueous extract showed effects between 0.45 and 0.84 mg/mL, whereas L-AgNPs showed effects between 0.09 and 0.34 mg/mL across bacteria. To the best of our knowledge, this is the first report on the silver nanoparticle-synthesizing potential of Leucas lanata , highlighting its promising applications in biomedical and pharmaceutical fields.