Biosynthesized Ag–ZnO nanohybrids exhibit strong antibacterial activity by inducing oxidative stress

Abstract

We report facile biosynthesis of Ag–ZnO nanohybrids consisting of Ag nanoparticles decorated ZnO nanobullets prepared by decorating wet chemically synthesized ZnO nanobullets with Ag nanoparticles through bioreduction of Ag + ions with aqueous extract of Piper nigrum fruits. The prepared nanomaterials were well characterized by FESEM, TEM, HRTEM, EDX, XRD, XPS, PL and UV–vis spectroscopy. FESEM and TEM analyses on the nanohybrids revealed ∼18 nm Ag nanoparticles decorating ZnO nanobullets with average size ∼48 nm. XRD results revealed hexagonal wurtzite ZnO with 22.4 nm crystallite size and FCC Ag with 18.7 nm crystalline size. Ag–ZnO nanohybrids exhibited strong antibacterial action against Escherichia coli, Bacillus oceanisediminis and Pseudomonas entomophila and efficiently inhibited their growth at 100 μg/mL, 50 μg/mL and 125 μg/mL, respectively. The molecular basis of antibacterial action of Ag–ZnO nanohybrids against E. coli was investigated using different biochemical and molecular assays. Addition of antioxidant histidine suppressed the antibacterial action of Ag–ZnO nanohybrids towards E. coli due to its ROS scavenging action. Bradford assay results showed enhanced protein leakage from Ag–ZnO nanohybrids treated E. coli, while TBARS assay results confirmed lipid peroxidation triggered by ROS. SEM on Ag–ZnO nanohybrids treated E. coli confirmed significant damage to the cell wall leading to morphology change. The antibacterial activity of Ag–ZnO nanohybrids against E. coli is mainly due to the ROS-induced oxidative stress, which caused enhanced lipid peroxidation, cell wall damage leading to significant protein leakage and DNA fragmentation.