Microfluidic vs. batch biosynthesis of contaminant-free, monodisperse silver nanoparticles using Verbenaceae extract for biomedical applications

Abstract Metal nanoparticles (NPs) with controlled size and morphology are growing attention in biomaterial science due to their high surface-to-volume ratio, tunable optical properties, and enhanced catalytic and antimicrobial activity. Monodisperse NPs exhibit more predictable physicochemical properties compared to polydisperse systems. In this study, phytochemicals from Verbenaceae plant extracts were used for the one-step environmental-friendly phytosynthesis of silver nanoparticles. A microfluidic (on-chip, OC) approach was applied to obtain more stable, and more uniformly distributed nanoparticles, and was compared with a conventional in-batch (IB) method. The AgNPs were characterized mainly using ultraviolet-visible spectrophotometry (UV-VIS), scanning transmission electron microscopy (STEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffractometry (XRD). Furthermore, the antimicrobial activity of AgNPs against Staphylococcus aureus , Escherichia coli , and Candida albicans was assessed. UV–Vis spectroscopy confirmed nanoparticle formation through SPR bands at 384–472 nm (IB) and 422–472 nm (OC), indicating the reduction of Ag⁺ to Ag⁰. FTIR spectra revealed functional groups of polyphenols and flavonoids responsible for nanoparticles reduction and capping. XRD patterns showed crystalline Ag with reflections at 2θ ≈ 38° and 44°, corresponding to planes (111) and (200), and crystallite sizes consistent with STEM results (11–69 nm). Microfluidic synthesis generally produced smaller and more uniformly distributed nanoparticles than the batch method, with differences in colloidal stability observed between systems. The AgNPs exhibited strong antimicrobial activity against Staphylococcus aureus (inhibition zone: 23–26 mm), Escherichia coli (inhibition zone: 17–21 mm), and Candida albicans , with complete inhibition for selected samples. These findings demonstrate that controlled microfluidic biosynthesis enhances nanoparticle uniformity while maintaining high antimicrobial efficacy, supporting sustainable strategies for noble metal nanoparticle production for potential biomedical applications.