Synthesis of Silver Nanoparticles Using Extract of Weeds and Optimized by Response Surface Methodology to the Control of Soil Pathogenic Bacteria Ralstonia solanacearum

Abstract

Extracts of leaf from five native Chilean weeds were evaluated in the biosynthesis of silver nanoparticles. The synthesis was monitored by UV-Vis spectra at 420 nm by typical formation of surface plasmon resonance. Moreover, the extract with major potential for the formation of nanoparticles was used to optimize the synthesis processes by response surface methodology, to obtain nanoparticles of small sizes by combination of three parameters (AgNO₃ and leaf extract concentrations and pH). Characterization of AgNPs was made by TEM, XRD, and DLS. The inhibitory activity was evaluated by disk diffusion method and minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined. Only two out of five extracts evaluated (Hypericum perforatum and Malva nicaensis) showed capacity to biosynthesize AgNPs. pH 10, AgNO₃ (1 mM), and leaf extract at 5% vv⁻¹ were the optimal conditions to synthesize small AgNPs (< 40 nm). Inhibition zone from diffusion disk assay, MIC (30 μg mL⁻¹) and MBC (40 μg mL⁻¹), revealed a high antibacterial activity of AgNPs against Ralstonia solanacearum. Based on the results, the AgNPs biosynthesized from the leaf extract of H. perforatum is a promising antibacterial agent for its use in the control of R. solanacearum.