Green synthesis of silver nanoparticles using persimmon peel extract and the stabilizing role of trehalose: Characterization, antimicrobial and antioxidant activities

This study reports the green synthesis of silver nanoparticles (AgNPs) using water extract of persimmon peel (PE) and evaluates the stability of trehalose on the nanoparticles characteristics, potential antimicrobial and antioxidant activities as well as post-freeze drying stability. The total phenolic and flavonoid contents of the PE extract were also investigated. Trehalose (Th) was introduced after nanoparticle formation as a cryoprotectant to compare its effectiveness in stabilizing AgNPs without (PE-AgNPs) and with trehalose (PE-Th-AgNPs) after free-drying treatment. After 5-hours synthesis, AgNPs showed a maximum absorption peak at 432 nm in the UV-Visible spectrum, confirming the nanoparticles formation. Scanning and transmission electron microscopy micrographs revealed predominantly spherical nanoparticles, while dynamic light scattering analysis showed large z-average size and > 0.3 PDI values, indicating the presence of capping agents from both trehalose and phytochemicals in PE extract as well as partial aggregation. Energy dispersive X-rays analysis confirmed a strong silver signal with trace amounts of other elements, corresponding to the composition of PE extract. Furthermore, total phenolic and flavonoid contents of PE extract were low, which was related to the use of water as extraction solvent and other extraction parameters. Following the characterization, antimicrobial activity of synthesized AgNPs toward representative microorganisms by agar well diffusion method showed moderate inhibition zones, with stronger activity observed for PE-Th-AgNPs compared to PE-AgNPs. The synthesized AgNPs also exhibited DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging activity, indicating low antioxidant effect. The presence of trehalose resulted in a moderate increase in particle size with improved inhibition zones, DPPH scavenging activity, and better redispersibility after freeze-drying compared to PE-AgNPs without trehalose.