Optimization of green synthesis parameters for silver nanoparticles using <i>Cleistocalyx operculatus</i> via Box–Behnken design and antibacterial evaluation

Abstract In this study, the authors performed the extraction of Cleistocalyx operculatus ( C. operculatus ) leaves, obtaining an extract with a total polyphenol content of 141.646 mgGAE g −1 dried leaf. The condition was optimized for silver nanoparticle synthesis using the Box–Behnken model with 5 factors and 2 objective functions. The results showed the optimized synthesis conditions: 1.543 mM AgNO 3 concentration, a volume ratio of AgNO 3 solution to leaf extract of 7.514, a leaf extract volume of 3.362 ml, a temperature of 48.902 °C, and a time of 50.956 min. The silver nanoparticle solution was synthesized from the AgNO 3 precursor solution under optimal conditions, using an ethanol–water extract from C. operculatus leaves as the reducing agent. The formation of silver nanoparticles was observed using a Field Emission Scanning Electron Microscopes, measuring particle size and the polydispersity index, as well as UV–vis absorption spectra. The analysis results showed that the synthesized silver nanoparticles had a size of approximately 20–70 nm, with a UV–vis absorption peak at 445 nm. Additionally, these silver nanoparticles exhibited the ability to inhibit Staphylococcus aureus and Pseudomonas aeruginosa bacteria, with inhibition zone diameters of 12 mm and 16 mm, respectively. The research results indicate the potential application of green nanotechnology in the treatment of bacterial infections.