Utilizing Plackett–Burman and Box–Behnken Designs for Plant Extract–Based AgNP Synthesis Optimization: Unveiling Antifungal Potential Against Phytophthora Species

This study optimized a green synthesis method for silver nanoparticles (AgNPs) using aqueous extracts of black tea, linden, cherry laurel, kale, and melocan, employing a statistical design of experiments. The plant extracts acted as bio-reducing agents. Total and individual phenolic compounds in the extracts were quantified using ultraviolet-visible (UV–Vis) spectroscopy and ultra-high-performance liquid chromatography (UHPLC). AgNP yields were maximized through a combination of Plackett–Burman and Box–Behnken designs. The synthesized AgNPs were characterized by UV–Vis spectroscopy, Fourier transform infrared (FT–IR) spectroscopy, scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM). Optimal AgNP production was achieved under the following conditions (determined by response surface methodology, RSM): 9.6 g of plant material, extraction heating at 80°C for 20 minutes, 10 mM AgNO3, 2.5 mL of extract, 800 W microwave irradiation, and a 90-second reaction time. FT–IR analysis confirmed the role of phenolic compounds in reducing and stabilizing AgNPs. The resulting AgNPs exhibited uniform spherical morphology, with average particle sizes of 5.30 nm (black tea), 8.74 nm (linden), 7.20 nm (cherry laurel), 6.32 nm (kale), and 9.44 nm (melocan). Antifungal assays against five Phytophthora species revealed that kale-derived AgNPs were most potent, with EC50, MIC, and MFC values ranging from 9.28–30.84 µg mL−1, 200–300 µg mL−1, and 200–400 µg mL−1, respectively. These results suggest that plant-extract-synthesized AgNPs offer a sustainable approach to managing Phytophthora diseases, warranting further research.