Biosynthesis of Zinc Oxide Nanoparticles Using Plant Extracts of Aloe vera and Hibiscus sabdariffa: Phytochemical, Antibacterial, Antioxidant and Anti-proliferative Studies

Abstract

The zinc oxide (ZnO) nanoparticles were successfully synthesized by using aqueous extracts of Aloe vera gel/leaf and Hibiscus sabdariffa leaf, and characterized by FT IR, UV-Vis, XRD, SEM, and EDX techniques. For comparison purposes, ZnO nanoparticles was also synthesized by chemical method. Phytochemical screening of the A. vera gel and leaf and H. sabdariffa leaf extracts showed the presence of alkaloids, carbohydrates, flavonoids, gums and mucilages, saponins, phenolic compounds, tannins, and terpenoids. FT IR spectra showed the presence of functional groups and protein as the stabilizing agent surrounding the ZnO nanoparticles. UV-Vis spectra of ZnO nanoparticles exhibit the characteristic absorption band in the range of 344–360 nm, which can be assigned to the intrinsic bandgap absorption of ZnO due to the electron transitions from the valence band to the conduction band. Powder XRD patterns confirmed the hexagonal wurtzite structure. Further, the SEM analysis also indicates the hexagonal rod shape structure of the ZnO nanoparticles. EDX spectra confirmed the chemical composition of the ZnO nanoparticles synthesized by both biological and chemical methods. In vitro antibacterial activity of ZnO nanoparticles synthesized by both biological and chemical methods were performed on three Gram (−ve) (Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa) and one Gram (+ve) (Staphylococcus aureus) bacteria, in which the ZnO nanoparticles obtained by biological method showed excellent bactericidal activity over that obtained by chemical method. All the ZnO nanoparticles showed promising antioxidant activity determined by five different methods such as 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS); 2,2′-diphenyl-1-picrylhydrazyl (DPPH); hydrogen peroxide (H2O2); superoxide radical scavenging; and hydroxyl radical scavenging assays. In vitro cytotoxicity of the ZnO nanoparticles were tested against three cancerous cell lines such as human breast adenocarcinoma (MCF-7), cervical (HeLa) and epithelioma (Hep-2), and one normal human dermal fibroblasts (NHDF) cell lines by MTT assay. Apoptosis induction was further confirmed by flow cytometry and cell cycle arrest. The ZnO nanoparticles obtained by biological method display remarkable cytotoxicity against the MCF-7 cell line, and found to be more potent than the widely used drug cisplatin.