Ultrasound-assisted green synthesis of gold nanoparticles using Pelargonium graveolens leaf extract: Antibacterial activity and microfluidic evaluation of mechanistic effects

Green chemistry enables sustainable, innovative, and efficient nanomaterial synthesis advancements. In this work, a green synthesis approach was employed to produce gold nanoparticles (Au NPs) using an ultrasound-assisted method with aqueous Pelargonium graveolens leaf extract. The resulting Au NPs were characterized by UV-Vis spectroscopy, X-ray diffraction, dynamic light scattering, and transmission electron microscopy, confirming cubic, stable particles with an average size of ∼41.5 nm, a zeta potential of +19.4 mV, and an absorption peak at 525 nm. Antibacterial activities of both the Au NPs and plant extract were evaluated against B. subtilis, S. aureus, E. coli, and P. aeruginosa, using conventional and microfluidic assays. Au NPs demonstrated superior efficacy (e.g., MIC for E. coli 1.56 μg/mL). Nucleic acid and protein leakage assays indicated greater membrane disruption in the microfluidic system compared to the conventional method. SEM imaging revealed substantial bacterial cell wall disruption, validating the significant antibacterial mechanisms of biosynthesized Au NPs.