Biogenic Nanoparticles of Co, Zn, Se and Ni via <i>Shorea robusta</i> Extract: Comparative Insights into Antimicrobial, Antioxidant and Toxic Effects

Using Shorea robusta flower extract (SRE) as a stabilizing and reducing agent, this study investigated the environmentally friendly synthesis of metal nanoparticles (NPs). Four metal NPs, namely cobalt (CoNPs), nickel (NiNPs), selenium (SeNPs) and zinc nanoparticles (ZnNPs) were synthesized. These NPs were characterized using UV-Vis spectroscopy and FTIR. The UV–Visible spectra confirmed successful synthesis with characteristic absorption peaks within [Formula: see text]270–285 nm of all NPs. FTIR analysis revealed the presence of functional groups such as –NH, –OH, C[Formula: see text]O and C–O, indicating phytochemical-mediated reduction and stabilization of the nanoparticles. The antibacterial and antioxidant properties of the synthesized NPs were assessed. SeNPs exhibited superior antibacterial activity compared with the other NPs, demonstrating a zone of inhibition against Staphylococcus aureus and Escherichia coli. Antioxidant potential was assessed using DPPH, ABTS and phosphomolybdate assays, where SeNPs consistently demonstrated superior radical scavenging activity with [Formula: see text]94% inhibition in the DPPH assay at 100 μg/mL. Toxicity evaluation using the brine shrimp lethality assay indicated a concentration-dependent effect, with SeNPs showing relatively lower toxicity than other NPs. These findings highlight the biomedical potential of green-synthesized SeNPs, particularly for antibacterial and antioxidant therapies. This study supports the use of S. robusta as a sustainable and effective source for the eco-friendly synthesis of multifunctional nanoparticles.