Green synthesis, characterization and antimicrobial activity of zinc oxide quantum dots using Eclipta alba

The present study focused on the green and sustainable synthesis of zinc oxide (ZnO) quantum dots (QDs) using zinc acetate (precursor) and Eclipta alba leaf extract as a reducing agent. The synthesis of ZnO QDs was monitored by ultraviolet–visible absorption spectroscopy at wavelength (λ_max) 324 nm. The optimal synthesis of ZnO QDs was recorded at temperature 40 °C, pH 7, 5 mL zinc acetate (5 mM), 7 mL leaf extract and reaction time of 75 min. The transmission electron microscopy (TEM) depicted homogeneous distribution of spherical ZnO QDs with mean particle size of 6 nm that comparable to biomolecules. The selected area electron diffraction (SAED) analysis revealed crystalline nature of ZnO QDs having a hexagonal wurtzite phase with lattice constants a = b = 0.32 nm and c = 0.52 nm. Furthermore, the physical interactions between ZnO QDs and E. coli cells were studied by TEM and agar well diffusion methods that showed enhanced antimicrobial activity. Overall, these unique size and quite stable QDs open up possibilities of applications in a number of commercial consumers, clinical products and fluorescence labeling including the antimicrobial agent.