Green synthesis of silver-based micro-composites using Xylopia aethiopica extracts and their antibacterial activity against Staphylococcus aureus

Abstract

The prevailing emphasis on nanoscale materials has often overlooked the functional potential of microscale particulate systems. In this study, silver-based micro-composites produced via plant-mediated silver reduction were evaluated for antimicrobial properties. Silver microparticles were synthesized using aqueous extracts of the fruits, stem, and leaves of Xylopia aethiopica, and subsequently incorporated into chitosan and starch matrices to form polymer-associated micro-composites. The resulting materials were characterized using Fourier-transform infrared spectroscopy (FTIR), scanning and transmission electron microscopy (SEM and TEM), energy-dispersive X-ray spectroscopy (EDX), and ImageJ-based particle size analysis. Antimicrobial performance against Staphylococcus aureus was assessed using the disc diffusion assay as a qualitative comparative screening method. The synthesized materials exhibited particle sizes ranging from 0.938 μm to 47.406 μm, with starch encapsulation generally producing larger but more porous composites than chitosan encapsulation. Notably, the starch-encapsulated stem-derived composite (STR-XASMP) produced the largest inhibition zone (42 mm) under diffusion assay conditions. Given the diffusion-dependent nature of the assay, these observations are interpreted as consistent with enhanced material–bacterium interactions and potential release of active species.The findings suggest that porosity and surface architecture may contribute to the apparent antimicrobial performance of micron-scale composites, highlighting an alternative design space beyond strict nanoscale size reduction. Quantitative antimicrobial assays, release kinetics, and safety evaluations are required to confirm these observations and are the focus of ongoing work.