Antimicrobial Activity of Green-Synthesized Iron Oxide Nanoparticles Using Guiera senegalensis Stem Bark Extract

Rising antimicrobial resistance and the drawbacks of conventional nanoparticle synthesis have increased interest in environmentally benign routes to biologically active nanomaterials. Here, iron oxide nanoparticles (IONPs) were biosynthesized using an aqueous stem-bark extract of Guiera senegalensis, and their antimicrobial activity against selected bacterial and fungal pathogens was evaluated. A freshly prepared 0.01 M FeCl₂ solution (50 mL) was added to 100 mL of extract under continuous stirring, and the mixture was held at approximately 60 °C for 30 min. The nanoparticles were recovered by centrifugation, washed, dried at 70 °C and gently ground. The product was characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). FTIR spectra showed absorption bands at approximately 3335, 2920, 1718, 1625, 1408, 1035 and 565 cm⁻¹, assigned mainly to O–H, C–H, C=O, aromatic/oxygen-containing groups, O–H bending/C–O, and Fe–O vibrations, respectively. The Fe–O band near 565 cm⁻¹ supported the formation of an iron oxide phase, and the remaining bands pointed to plant-derived phytochemicals acting as stabilizing agents. XRD reflections at approximately 30.2°, 35.5°, 43.3°, 53.5°, 57.4° and 62.8° (2θ) were consistent with spinel-type iron oxides such as magnetite and maghemite, and SEM revealed predominantly rounded to approximately spherical particles with some aggregation. The nanoparticles inhibited Escherichia coli, Staphylococcus aureus, Candida albicans and Aspergillus niger in a concentration-dependent manner; at 100 µg/L, the inhibition zones were 16, 18, 9 and 13 mm, respectively. S. aureus was the most susceptible organism and C. albicans the least. These results show that G. senegalensis stem-bark extract can mediate the synthesis and stabilization of iron oxide nanoparticles with measurable, broad-spectrum in vitro antimicrobial activity.