Characterization and antibacterial effect of green-synthesised silver nanoparticles using different extraction methods from Ziziphus spina-christi (Sidr) leaf extract collected from Syria

Abstract

The study investigates the effective green biosynthesis of silver nanoparticles (AgNPs) from silver nitrate (AgNO₃) as a precursor using Syrian Sidr leaf extract as a reducing and stabilizing agent. Three extraction methods (Maceration, ultrasound-assisted, and Soxhlet) were tested using six solvents. The Soxhlet method with a methanol/water mixture (60 : 40) provided the highest phenolic (192.83 ± 0.3 mg g⁻¹) and flavonoid (59.48 ± 7.45 mg g⁻¹) yields and was selected for nanoparticle biosynthesis. Further characterization confirmed the synthesis using these analytical techniques. UV-Vis spectroscopy revealed the formation of ZL-AgNPs via a characteristic plasmon resonance peak at 430 nm; FTIR indicated surface functional groups from the plant extract; XRD confirmed a cubic crystalline structure with an average crystallite size of 11 nm; SEM images showed spherical particles below 20 nm; EDX analysis depicted a dominant silver signal (85 wt%) with minor contributions from organic compounds. The biosynthesised ZL-AgNPs exhibited significant antibacterial activity against Gram-positive bacterium Staphylococcus aureus and the Gram-negative bacterium Escherichia coli, with inhibition zones ranging from 13.76 ± 0.25 to 21.65 ± 0.34 mm for E. coli and 0 to 16.73 ± 0.21 mm for S. aureus at concentrations of 25–200 μg mL⁻¹. The positive control (Gentamicin, 200 μg mL⁻¹) showed the largest inhibition zones, while the plant extract control demonstrated moderate activity at higher concentrations. These findings confirm the distinctive physicochemical properties and strong antibacterial potential of ZL-AgNPs for prospective biomedical applications.