Preparation of ZnO nanoparticles from Juglans regia dry husk extract for biomedical applications

The worldwide problem of antibiotic resistance threatens public health, necessitating the search for antimicrobial agents that are not only effective against antibiotic-resistant bacteria but also harmless to the environment. Metal nanoparticles and their oxides are promising agents for battling antibiotic-resistant bacteria, and nanoparticles (NPs) of any size or form can be manufactured in high quality using low-cost and simple-to-follow processes that are friendly to the environment. The purpose of this study was to evaluate the antimicrobial activity of zinc oxide nanoparticles (ZnO NPs) that were synthesized using the extract of Juglans regia dried husk, a waste product. Extract components were used as capping and reducing agents in reactions with zinc acetate salt. The properties of ZnO NPs were examined using Fourier-transform infrared spectroscopy (FTIR), UV–visible spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray diffraction (XRD). The antibacterial activity ZnO NPs against Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, Klebsiella pneumoniae, and Candida albicans, which were isolated from patients with urinary tract infection, was assessed using the agar well diffusion method. ZnO NPs produced using the aqueous extract of Juglans regia dried husk had a band gap of 3.5 eV, which was determined using UV–visible spectra in the wavelength range of 200–1100 nm. The FTIR spectra of ZnO NPs, acquired in the range of 400–4000 cm⁻¹, contained bands corresponding to specific functional groups of biomolecules and metal oxides. X-ray patterns were acquired in the range of 2θ = 20° to 80°. The crystallite size of produced ZnO NPs, calculated using Scherrer’s formula, was 8.7 nm. The wurtzite hexagonal structure of ZnO NPs was confirmed by the presence of the wide band at 495 to 850 cm⁻¹. The peaks in the XRD pattern corresponded to the (100), (002), (101), (110), (103), and (201) planes. Prepared nanoparticles were semispherical, with a grain diameter of approximately 23 nm and mean roughness (Sa) of 1.65 nm. According to the results of antibacterial testing, ZnO NPs exhibited the greatest growth inhibition effect against Staphylococcus epidermidis, followed by Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, and Candida albicans (diameter of inhibition zones of 37 ± 0.89, 35.6 ± 0.52, 33.3 ± 1.36, and 35 ± 0.89 mm, respectively). ZnO NPs exhibited significant antibacterial activity owing to their distinct toxicity toward microorganisms. Hence, they can be applied as antimicrobial agents in medicine, surgery, diagnostics, and nanomedicine.