Biosynthesis and Characterisation of <scp> <i>Eucalyptus tereticornis</i> Essential oil (EO) </scp> Mediated <scp>ZnO</scp> Nanoparticle and Assessment of Their Antimicrobial, Antioxidant, and Membrane Stabilising Properties

ABSTRACT The biosynthesis of metal nanoparticles through essential oil‐mediated methods represents an innovative approach at the intersection of nanotechnology and natural products. The primary focus of this study was on the synthesis of Zinc oxide nanoparticles (ZnO NPs) by utilising the essential oil (EO) of Eucalyptus tereticornis species (Euc EO), as well as the investigation of the prospective biological applications of these nanoparticles. The synthesised Eucalyptus tereticornis EO mediated ZnO NPs (Euc ZnO NPs) were characterised by UV–Vis spectroscopy, Fourier Transform Infrared spectroscopy (FTIR), X‐Ray Diffraction (XRD), Thermogravimetric Analysis (TGA), and Scanning Electron microscopy (SEM) analysis (average size between 30 and 120 nm). The agar well diffusion method was used to test the antibacterial activity of an oil and biosynthesised nanoparticles, followed by Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) determinations. In comparison to pure Euc EO (100%), ZnO NPs showed efficient antibacterial activities against all tested microorganisms, with a maximum zone of inhibition for Bacillus cereus (24 mm) and high antifungal activities against Aspergillus fumigatus (23 mm) at 100 mg/mL. At 1000 μg/mL concentration, Euc ZnO NPs showed significant antioxidant activity, inhibiting 80.2% of free radicals compared to 76.43% for pure EO (100%). The membrane stabilising effect of Euc ZnO NPs was demonstrated with the high outcome at 3000 μg/mL, outperforming Acetylsalicylic acid. This study presents a method for synthesising efficient and rapid ZnO NPs using Eucalyptus tereticornis EOs, which utilise less toxic chemicals that have the potential to be used as an effective alternative to combat antibiotic resistance.