Medicinal Plants Extract for the Bio-Assisted Synthesis of Ag/AgCl Nanoparticles with Antibacterial Activity

Abstract

The increasing antibiotic resistance necessitates sustainable methods for synthesizing antibacterial nanoparticles. This study focuses on the bio-assisted synthesis of silver/silver chloride nanoparticles (Ag/AgCl-NPs) using aqueous extracts of Acalypha arvensis, Hampea rovirosae, and Inga jinicuil. Polyphenols and flavonoids were quantified, and functional groups were analyzed via Fourier-transform infrared to assess their influence on the properties of Ag/AgCl-NPs. The effects of thermal treatment at 60 and 500 °C on the NPs’ size, morphology, and antibacterial efficacy were assessed. UV–Vis spectroscopy indicated absorption peaks between 430 and 449 nm, while X-ray diffraction analysis confirmed the presence of metallic Ag and a cubic AgCl structure, with crystallite sizes ranging from 11–51 and 28–60 nm, respectively. Dynamic light scattering showed hydrodynamic sizes of up to 127.2 ± 0.9 nm at 60 °C and up to 348.9 ± 10.7 nm at 500 °C. Field emission scanning electron microscopy micrographs exhibited a quasi-spherical morphology with significant agglomeration; showing particle sizes between 55 ± 11 and 81 ± 28 nm at 60 °C, and up to 135 ± 65 nm at 500 °C. X-ray photoelectron spectroscopy confirmed the metallic silver (Ag⁰), organic molecules, and absorbed chlorides on the NP surface. Pearson correlation analysis indicated a strong positive correlation between polyphenol content and NPs yield (r = 0.922), while it indicated a strong negative correlation with flavonoid content (r = −0.996). Additionally, a negative correlation was found between hydrodynamic size and antibacterial activity against Staphylococcus aureus (r = −0.854). The Ag/AgCl-NPs, after drying at 60 and 500 °C, were tested against Escherichia coli and S. aureus with minimum bactericidal concentrations below 19 µg/mL against E. coli. Minimum inhibitory concentration (MIC) for Ag/AgCl-NPs synthesized with A. arvensis and H. rovirosae extracts were above 312 µg/mL for S. aureus, while those synthesized with I. jinicuil showed MIC as low as 156 µg/mL. These results highlight the potential of medicinal plant extracts in the synthesis of Ag/AgCl with enhanced antibacterial properties.