Plant-Mediated Synthesis of Silver Nanoparticles Using Salvia tomentosa: Characterization and Evaluation of Their...

This study reports the green synthesis of silver nanoparticles (AgNPs) using Salvia tomentosa L. leaf extract, and evaluates their physicochemical characteristics and biointerfacial performance, including DNA interaction, antibacterial activity, and antioxidant capacity. AgNP formation was confirmed by UV-Vis spectroscopy through a surface plasmon resonance band at 472 nm. SEM imaging showed predominantly spherical particles with sizes of 30-80 nm and a zeta potential of -17.3 mV, and EDX verified the elemental presence of silver. FTIR spectra indicated that plant-derived biomolecules, particularly phenolics, contributed to the reduction and capping/stabilization of AgNPs. XRD analysis confirmed a crystalline face-centered cubic structure. The AgNPs exhibited moderate, spontaneous binding to DNA (Kb ≈ 1.07 × 10⁴ M^-1), characterized by pronounced hyperchromism without evidence of intercalation. Competitive fluorescence assays supported a predominantly non-intercalative, surface-associated interaction with minor groove perturbation, while agarose gel electrophoresis indicated preserved plasmid integrity and no extensive strand cleavage. Collectively, these results suggest reversible and structurally non-destructive AgNP-DNA complexation, indicating their potential for nucleic acid-related nano-biointerface studies, while further investigations are required to evaluate their suitability for biomedical applications. The biosynthesized AgNPs showed enhanced antibacterial activity against Gram-positive (Bacillus cereus) and Gram-negative (Pantoea agglomerans) bacteria compared with the leaf extract, whereas AgNO₃ produced the strongest immediate effect, consistent with rapid Ag⁺ release. Antioxidant activity assessed by DPPH and ABTS assays showed strong radical-scavenging activity for the extract, in line with its high total phenolic content (206.2 mg GAE/g). Although AgNPs displayed lower phenolic content (164.2 mg GAE/g) and reduced antioxidant activity than the extract, they retained moderate scavenging capacity, indicating effective surface functionalization by phytochemicals. Overall, S. tomentosa leaf extract-capped AgNPs combine defined physicochemical features with non-destructive DNA association and antibacterial efficacy, underscoring their promise as phytochemical-functionalized nano-biointerfaces for antimicrobial and related biointerface applications.