Green synthesis of nanoparticles using cottonwood and rambutan honeys: Optimization, characterization, and enhanced antioxidant activity with reduced toxicity via oligochitosan coating

The green synthesis of silver nanoparticles (AgNPs) using bio-based reductants has gained significant attention due to its environmentally friendly and sustainable approach. This study aims to optimize the synthesis, characterize the physicochemical properties, and evaluate the biological activities of AgNPs synthesized using cottonwood (Ceiba pentandra) and rambutan (Nephelium lappaceum) honeys as bioreducing agents, with further functionalization by oligochitosan to enhance stability and bioactivity. Comprehensive characterization using UV-Vis spectroscopy, FTIR, PSA-DLS TEM, FESEM-EDX, and XRD confirmed the formation of spherical nanoparticles with an average size of 9.01 nm. The particle size distribution followed a lognormal model with an R² value of 0.925, indicating high statistical reliability. The biological activities of AgNPs and AgNPs-Ch composites were evaluated through antioxidant and toxicity assays. The DPPH assay demonstrated a 3.00–3.41-fold enhancement in antioxidant activity upon chitosan coating, suggesting a synergistic interaction between AgNPs and oligochitosan in free radical scavenging. Furthermore, toxicity assessment using Artemia salina nauplii revealed a substantial 6.12–6.19-fold reduction in toxicity for AgNPs-Ch compared to uncoated AgNPs, highlighting the protective role of chitosan in mitigating silver ion release. These findings underscore the potential of honey-derived AgNPs and their chitosan composites for biomedical and environmental applications, providing a sustainable route for nanoparticle synthesis with improved biofunctionality and safety.