Green synthesis of silver nanoparticles using banana flower extract, and their antibacterial activity

Silver nanoparticles (AgNPs) were synthesised using banana flower extract (BFE) as a reducing and stabilising agent. Spherical, well-dispersed, and stable AgNPs were formed and characterised by ultraviolet-visible spectroscopy (UV-vis), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), thermal gravimetric analysis (TGA), and zeta potential. The in vitro antimicrobial properties of AgNPs against Staphylococcus aureus and Escherichia coli were then investigated. The minimum inhibitory concentration (MIC) of AgNPs against S. aureus and E. coli were 32 and 16 μg/mL, respectively. E. coli was more sensitive to AgNPs than S. aureus due to differences in cell wall structures of the bacteria. Regarding the bactericidal mechanisms of AgNPs, an increase in cell permeability and a distinctive deformation in cellular morphology was observed. The antibacterial effect decreased with the addition of the antioxidant N-acetyl-l-cysteine (NAC) which acted as ROS scavenger. In summary, the antibacterial mechanism was likely a combination of cell membrane damage and ROS induction.