Synergistic effect of Foeniculum vulgare essential oil on the antibacterial activities of Ag- and Cu-substituted ZnO nanorods (ZnO-NRs) against food, human and plant pathogenic bacterial disease agents

Abstract

• Bare, Ag- and Cu-substituted ZnO-NRs were successfully synthesized. • XRD measurements were clearly presented the sharp ZnO phase. • ZnO-NRs enriched with plant-derived EOs were provided synergistic antibacterial activity. In the present work, bare, Ag- and Cu-substituted ZnO nanorods (ZnO-NRs) were prepared by a simple, low-cost synthesis temperature and inexpensive solution-based growth method with low synthesis temperature. In addition to the physical properties of the bare, Ag- and Cu-substituted ZnO-NRs, the antibacterial activities of fennel essential oil (EO) incorporated into the ZnO-NRs against opportunistic food (Pseudomonas aeruginosa and Bacillus subtilis) and plant pathogenic (Pseudomonas syringae pv. phaseolicola) bacterial disease agents were also investigated. X-ray diffraction patterns showed the hexagonal wurtzite phase of ZnO. FESEM images confirmed the production of nanorod-like morphology with an average diameter of about 200 nm. The antibacterial activities of the bare, Ag- and Cu-substituted ZnO NRs varied depending on the bacterial isolates tested. The highest antibacterial activity was detected against the Gram-positive bacterial isolate Bacillus subtilis. The antibacterial activities were significantly enhanced by doping the bare ZnO NRs with Cu and Ag. This enhancement is more pronounced for Cu-substituted ZnO-NRs (up to 161.1%) than for Ag-substituted ZnO-NRs (up to 32.5%). Although fennel EO and bare ZnO-NRs possess antibacterial activities, the antibacterial activities of bare, Ag- and Cu-substituted ZnO-NRs increased dramatically after the incorporation of fennel EO. This increase is more significant for EO incorporated Cu-substituted ZnO-NRs (213.3%) than for Ag-substituted ZnO-NRs (up to 52.7%). In conclusion, doping bare ZnO-NRs with Cu and Ag resulted in superior antibacterial activity, while incorporating fennel EO into bare, Cu- and Ag-substituted ZnO-NRs led to a synergistic effect in terms of their antibacterial activities.