Green synthesis of zinc oxide silver nanoparticles using punica granatum for antibacterial and anticancer applications

Abstract

The problem of antimicrobial resistance (AMR) is expected to become a much worse issue as more microbes have developed resistance to conventional drugs. Thus, making medical treatments more complicated than usual. Similarly, cancer disease has been projected to affect a large number of human populations in the next few decades, resulting in increased morbidity and mortality worldwide. The field of nanotechnology has been thriving as it shows potential to ameliorate these growing concerns. Metallic nanomaterials such as zinc oxide nanoparticles (ZnO-NPs) and silver nanoparticles (Ag-NPs) are interesting materials to study as they possess great physical and chemical properties that could contribute in antibacterial and anticancer applications. Individual ZnO-NPs and Ag-NPs exhibit excellent activities in various field but there is still a lack of information on the efficiency of biologically synthesized coupled zinc oxide silver nanoparticles (ZnO-Ag-NPs) for use as antibacterial or anticancer agent. In this research, the “green” synthesis of ZnO-NPs and ZnO-Ag-NPs in the presence of Punica granatum (pomegranate) fruit peels extract under different parameters is reported. P. granatum fruit peels extract contains an abundance of phytochemicals that can act as a reducing or stabilizing agent during NPs synthesis process. Characterization of synthesized samples were carried out using X-ray diffraction (XRD), UV-visible (UV-vis) spectroscopy, High Resolution Transmission Electron Microscopy (HR-TEM) and Fourier Transform Infrared spectroscopy (FTIR). Sol-gel as well as combustion method was adopted for the synthesis of ZnO-NPs and the effect of calcination temperatures (400, 500, 600 and 700 °C) on the physico-chemical properties of ZnO-NPs was investigated. Crystallinity and particle sizes of the biosynthesized ZnO-NPs increased proportionally with calcination temperature. Subsequently, ZnO-Ag-NPs was synthesized using precipitation method in acidic, neutral and alkaline medium reaction (pH 5, pH 7 and pH 9 respectively) with P. granatum F. peels extract as a reducing/stabilizing agent. The role of pH during synthesis process of ZnO-Ag-NPs was evaluated and discussed accordingly. XRD confirmed the production of highly pure ZnO-Ag-NPs with increased crystallinity for samples in higher pH level. UV-vis analysis displayed shifting of absorption peaks of ZnO-Ag-NPs towards higher wavelength and a decrease in band-gap energy compared to pure ZnO-NPs, further confirming the coupling of Ag-NPs onto ZnO-NPs. For antibacterial studies, ZnO-Ag-NPs showed significantly high inhibition activities of both Gram-positive and Gram-negative bacterial strains compared to pure ZnO-NPs. The proposed mechanism of this enhanced antibacterial activities was further elaborated. In vitro cytotoxicity studies of the biosynthesized ZnO-NPs and ZnO-Ag-NPs against human colorectal cancer cell and normal colon cell were investigated but results showed non-selective killing of cells for both NPs. To conclude, pomegranate-mediated ZnO-Ag-NPs proves to be efficient as antibacterial agent, however, further modifications are required to give the NPs better specificity for cancer killing activities.